Calibration transfer in chemiluminescence analysis

2001

Abstract Direct standardization (DS) and piecewise direct standardization (PDS) methods are applied to multivariate standardization of chemiluminescence signals using PLS model as the calibration model. The linear concentration interval of the chemiluminescence determination was determined. This interval was located using univariate robust calibration by least median of squares (LMS) method. The linear calibration model was corroborated by conventional least-squares method. The standardization subset and window size were optimized by means of the prediction residual error sum of squares. Several instrumental sources of variability have been studied: the detection cell, instrument, batch ver…

A new selective method for dimethylamine in water analysis by liquid chromatography using solid-phase microextraction and two-stage derivatization wi…

2005

Abstract A new method is presented for the determination of DMA in water as its 9-fluorenylmethyl chloroformate (FMOC) derivative using solid-phase microextraction (SPME) and liquid chromatography. The method is based on the employment of SPME fibres coated with carbowax-templated resin (CW-TR) for analyte extraction and derivatization. The fibres were successively immersed in the samples, in a solution of o -phthalaldialdehyde and N -acethyl- l -cysteine (OPA–NAC) and finally, in a solution of FMOC. OPA–NAC reacted on the fibre with possible primary aliphatic amines present in the samples, particularly with PA which is a direct interferent in the determination of DMA with FMOC. In such a w…

Peptide Metal–Organic Frameworks for Enantioselective Separation of Chiral Drugs

2017

We report the ability of a chiral Cu(II) 3D MOF based on the tripeptide Gly-L-His-Gly (GHG) for the enantioselective separation of metamphetamine and ephedrine. Monte Carlo simulations suggest that chiral recognition is linked to preferential binding of one of the enantiomers as result of either stronger or additional H-bonds with the framework that lead to energetically more stable diastereomeric adducts. Solid phase extraction (SPE) of a racemic mixture by using Cu(GHG) as extractive phase permits isolating more than 50% of the (+)-ephedrine enantiomer as target compound in only four minutes. To the best of our knowledge, this represents the first example of a MOF capable of separating ch…

Sensitive determination of probenecid in urine samples by reversed-phase liquid chromatography and UV-visible detection using solid-phase extraction …

1993

This study describes a rapid method for the determination of probenecid in human urine by liquid chromatography with UV detection at 254 nm, after clean-up through a C8 solid-phase extraction column. Liquid chromatography was carried out on a C18-bonded phase using an acetonitrile-acetate buffer (pH=4) gradient elution. Ethacrynic acid was used as internal standard. The system has been applied to the determination of probenecid in the 0.10–100.0 μg/ml concentration range; the limit of detection was 5 ng/mL.

Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification of…

2001

Abstract Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicular drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimization, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compound. For chromatography, LiChrospher 100 RP 18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-β-cyclodextrin (the chiral selector) were use…

Derivatization of ephedrine with o-phthaldialdehyde for liquid chromatography after treatment with sodium hypochlorite.

2000

The usefulness of the reaction with NaClO followed by derivatization with o-phthaldialdehyde (OPA) and N-acetyl-L-cysteine (NAC) has been investigated for the chromatographic analysis of ephedrine. The influence of parameters affecting the two-stage reaction has been evaluated, including concentration of NaClO, time of reaction, temperature and pH. On the basis of these studies, conditions for the pre-column and (automated) post-column determination of ephedrine are presented. The described conditions have been applied to the measurement of ephedrine in the concentration intervals 0.2-20.0 microg/ml and 2.0-50.0 microg/ml for the pre-column and post-column methods, respectively. The possibi…

Miniaturized liquid chromatography coupled on-line to in-tube solid-phase microextraction for characterization of metallic nanoparticles using plasmo…

2018

Abstract This tutorial aims at providing guidelines for analyzing metallic nanoparticles (NPs) and their dispersions by using methods based on miniaturized liquid chromatography with diode array detection (MinLC-DAD) and coupled on-line to in-tube solid-phase microextraction (IT-SPME). Some practical advice and considerations are given for obtaining reliable results. In addition, this work outlines the potential applications that set these methodologies apart from microscopy-related techniques, dynamic light scattering, single particle ICP-MS, capillary electrophoresis, field-flow fractionation and other chromatographic configurations, which are discussed and mainly seek to accomplish size …

In Situ Colorimetric Quantification of Silver Cations in the Presence of Silver Nanoparticles

2013

Silver ions (Ag(+)) can be quantified in situ in the presence of AgNPs by using a colorimetric sensing probe (3,3',5,5'-tetramethylbenzidine). Interestingly, it also enables detection of the Ag(+) adsorbed on the AgNP surface. This is relevant to design new methods to make AgNPs while ensuring the total reduction of Ag(+).

Fast blue B functionalized silica-polymer composite to evaluate 3,5-dihy-droxyhydrocinnamic acid as biomarker of gluten intake

2021

Celiac disease is an immune-mediated systemic disorder elicited by gluten and related prolamines in genetically susceptible individuals. The current treatment is a strict and lifelong gluten-free diet. However, compliance with the gluten-free diet is not always adequate and many food products contain low concentrations of gluten. The determination of dietary transgressions is a challenge for patients, physicians and dietitians. Alkylresorcinols (AR) have been proposed as sensitive and specific biomarkers of gluten consumption. In this work silica-polymer composites doped with fast blue B reagent (FB) have been used to estimate alkylresorcinols in biological samples. The proposed colorimetri…

Adsorbent phases with nanomaterials for in-tube solid-phase microextraction coupled on-line to liquid nanochromatography

2015

Following the present trends in miniaturization, a methodology that combines on-line In-Tube Solid-Phase Microextraction (IT-SPME) with Liquid Nanochromatography (nano-LC) and UV-vis diode array detection (DAD) was developed. This coupling was achieved by using two interconnected valves (i.e. conventional and micro-automatic valves) in the system of injection. As for IT-SPME, different materials, containing in some cases nanostructures or nanoparticles and in other cases polymeric adsorbent phases immobilized on capillary columns, were tested in order to improve extraction efficiencies of organic compounds; diclofenac was selected as the target analyte. Additionally, the transfer time of th…

Selective determination of trimethylamine in air by liquid chromatography using solid phase extraction cartridges for sampling.

2004

Abstract The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn ( 20 mm ×2.1 mm i.d., packed with 30 μm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column ( 125 mm ×4 mm i.d., LiChrospher 100 RP18, 5 μm), and monitored at 262 nm. The method was applied to …

A sustainable on-line CapLC method for quantifying antifouling agents like irgarol-1051 and diuron in water samples: Estimation of the carbon footpri…

2016

In this work, in-tube solid phase microextraction (in-tube SPME) coupled to capillary LC (CapLC) with diode array detection has been reported, for on-line extraction and enrichment of booster biocides (irgarol-1051 and diuron) included in Water Frame Directive 2013/39/UE (WFD). The analytical performance has been successfully demonstrated. Furthermore, in the present work, the environmental friendliness of the procedure has been quantified by means of the implementation of the carbon footprint calculation of the analytical procedure and the comparison with other methodologies previously reported. Under the optimum conditions, the method presents good linearity over the range assayed, 0.05-1…

New micromethod combining miniaturized matrix solid-phase dispersion and in-tube in-valve solid-phase microextraction for estimating polycyclic aroma…

2008

Abstract Miniaturized matrix solid-phase dispersion (MSPD) was developed for the extraction of common polycyclic aromatic hydrocarbons (PAHs) from bivalve samples (100 mg, dry weight). Additional clean-up and analyte enrichment was accomplished by in-tube solid-phase microextraction (SPME). For this purpose the extracts collected after MSPD were diluted with water and injected into a capillary column coated with the extractive phase. This capillary column was connected to the analytical column by means of a switching valve. Separation and quantification of the PAHs were carried out using a monolithic LC column and fluorescence detection. Since the in-tube SPME device allowed the processing …

Colorimetric determination of alcohols in spirit drinks using a reversible solid sensor

2018

Abstract A sensor for the colorimetric estimation of the alcoholic content has been developed based on the entrapment of the reagent (4-N,N-dioctylamino)-4‘-trifluoroacetylazobenzene (ETHT 4001) into polydimethylsiloxane (PDMS) modified with tretraethylorthosilicate (TEOS). When exposed to an alcoholic media, the sensor delivers ETHT 4001 so that it reacts with alcohols, resulting in a change in the solution color. The diffusion of the entrapped ETHT 4001 from the polymeric sensor to the working solution depends on the hydrophobicity of both the sensor matrix and the media, while the time of exposure determines whether the reagent reacts with methanol, or with methanol and ethanol. Thus, th…

Evaluation and elimination of the “blank bias error” using the H-point standard addition method

1992

Abstract The basis of the H-point standard addition method in the cases where the analyte determination requires the use of an absorbent reagent is considered. The method evaluates and eliminates the blank bias error present in such procedures by using the absorbance increment at two selected wavelengths as the analytical signal of the calibration graphs. Three different determinations were tested: the determination of proteins with the biuret method, thorium with thoron and of magnesium with Titan Yellow. These procedures are better described by the proposed method than by the traditional approach using absorbance values against reagent blank.

Estimation of diuretic drugs in biological fluids by HPLC

1992

This critical review of different methods proposed for the determination and screening of diuretics is directed mainly, because of its potential application, towards highperformance liquid chromatography.

On-line in-tube solid phase microextraction coupled to capillary liquid chromatography-diode array detection for the analysis of caffeine and its met…

2019

Abstract In-tube solid phase microextraction (IT-SPME) coupled on-line to capillary liquid chromatography with diode array detection provides a simple and fast analytical methodology for the simultaneous quantitation of caffeine and its three primary metabolites (theobromine, paraxanthine and theophylline) in micro samples of serum, saliva and urine matrices. The sample amount required for one analysis was only 2.5 μL of saliva, 6.25 μL of serum or 40 μL of urine, a requirement for its implementation in a hospital laboratory for preterm newborns, where sample availability is a major problem. In standard conditions, 25 μL of diluted saliva or serum (or 100 μL of urine) were processed by IT-S…

A solid colorimetric sensor for the analysis of amphetamine-like street samples.

2016

A solid sensor obtained by embedding 1,2-naphthoquinone-4-sulfonate (NQS) into polydimethylsiloxane/tetraethylortosilicate/silicon dioxide nanoparticles composite has been developed to identify and determine amphetamine (AMP), methamphetamine (MAMP), 3,4-methylenedioxymetamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA). The analytes are derivatized inside the composite for 10 min to create a colored product which can be then quantified by measuring the diffuse reflectance or the color intensity after processing the digitalized image. Satisfactory limits of detection (0.002–0.005 g mL−1) and relative standard deviations (<10%) have been achieved. The proposed kit has been successfu…

Standard addition method in FIA. Comparison between different assemblies

1999

A comparison between the different proposed methods to perform the standard addition in an on-line way (flow injection analysis) is made. The different assemblies (reverse and conventional FIA) and the employed standards in every method are compared. Three analyses were carried out, two of them were analyses of samples of pH indicators (methylorange and chlorophenol red) prepared at an acid pH, while the standards were prepared at a basic pH. The third analysis was the analysis of chloride in different synthetic waters with a perfectly known composition for all the ions present in the samples. Besides a new method to perform the on-line standard addition is proposed, trying to reduce the co…

Determination of theophylline and paraxanthine in urine samples by liquid chromatography using the H-point standard additions method

1992

Abstract The simultaneous determination of theophylline and paraxanthine in urine samples by the H-point standard additions method (HPSAM) is described. Samples are extracted with C 18 solid-phase extraction cartridges and chromatographed using a Hypersil C 18 -ODS column and a mobile phase consisting of acetonirile-phosphate buffer in the gradient elution mode. Under these conditions theophylline and paraxanthine are eluted with short retention times. Although their chromatographic peaks are overlapped and their spectra are very similar, the H-point standard additions method provides excellent results in the determination of both xanthines at therapeutic levels.

A direct Capillary Liquid Chromatography with electrochemical detection method for determination of phenols in water samples

2010

A fast and direct method based on the use of Capillary Liquid Chromatography (LC) with electrochemical (EC) detection has been described for phenols pollutants in water samples. Concretely, phenol, o-cresol, 2-chlorophenol and bisphenol A have been selected as target analytes. The combination of Capillary LC with EC detection avoided the necessity of preconcentration steps typically used in environmental analysis. The sample injected volume was 2 μL. The achieved detection limits were between 1 and 2 μg/L and the linear dynamic range was up to 50 μg/L for all studied phenols. The precision and uncertainty were satisfactory. The analysis time per sample was 10 min. The proposed procedure has…

New Tools for Characterizing Metallic Nanoparticles: AgNPs, A Case Study.

2015

Currently, transmission electron microscopy (TEM) is the main technique for estimating the sizes of spherical nanoparticles (NPs) and through them, their concentrations. This paper demonstrates for the first time that C18 reversed-phase capillary liquid chromatography (Cap-LC) coupled to diode array detection (DAD) has the potential to estimate mean concentrations of silver nanoparticles (AgNPs) and thereby determine their average size. Direct injection of the sample without previous extraction or separation steps is carried out. Only a unique standard with a known AgNP size is needed for the calibration. In a first approach, the new method has been tested over silver nanoparticles, produce…

o-Phthalaldehyde–N-acetylcysteine polyamine derivatives: formation and stability in solution and in C18 supports

2001

A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde-N-acetylcysteine (OPA-NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant (k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8 +/- 2 x 10(-2) min(-1) in solution versus 7.7 +/- 1.1 x 10(-4) min(-1) on the (C18) solid support. The results obtai…

Chemiluminescent method for detection of eutrophication sources by estimation of organic amino nitrogen and ammonium in water.

2006

An automatic method has been developed for the estimation of organic amino nitrogen (CH2-NH) and ammonium in water samples. We propose a continuous flow system in which nitrogen compounds react with hypochlorite reagent to produce chloramines. Subsequently, the mixture is mixed with luminol, generating a chemiluminescence signal. The signal emission at 425 nm, registered as a function of time, decreases as nitrogen concentration increases, due to the decrease on hypochlorite concentration. A large number of nitrogen compounds have been assayed and their sensitivities compared, in milligrams per liter nitrogen. The ammonium calibration graph, expressed as N, can be used for most of the assay…

Automated trace enrichment for screening and/or determination of primary, secondary and tertiary amphetamines in biological samples by liquid chromat…

1999

A rapid and simple liquid chromatographic method for the automated determination of amphetamines in biological fluids was developed. The proposed procedure is based on the injection of 250 microL of sample into a 20 x 2.1 mm id precolumn (packed with a 30 microns Hypersil C18 stationary phase) for enrichment and purification of the analytes. Next, the analytes are transferred to a 5 microns LiChrospher 100 RP18, 125 x 4 mm id analytical column for their separation under reversed-phase conditions. Water was used to eliminate the matrix components from the precolumn and a 0.2 M phosphate buffer (pH 3) containing 2% triethylamine was the mobile phase for the resolution of the amphetamines. The…

Rapid analysis of effluents generated by the dairy industry for fat determination by preconcentration in nylon membranes and attenuated total reflect…

2014

Abstract This paper describes a new approach for the determination of fat in the effluents generated by the dairy industry which is based on the retention of fat in nylon membranes and measurement of the absorbances on the membrane surface by ATR-IR spectroscopy. Different options have been evaluated for retaining fat in the membranes using milk samples of different origin and fat content. Based on the results obtained, a method is proposed for the determination of fat in effluents which involves the filtration of 1 mL of the samples through 0.45 µm nylon membranes of 13 mm diameter. The fat content is then determined by measuring the absorbance of band at 1745 cm −1 . The proposed method c…

A comparison of various calibration techniques applied to the ninhydrin-cefoxitin determination

1996

Abstract This report deals with spectrophotometric determination of cefoxitin from intact antibiotics or from its acid induced degradation product by means of their reaction with ninhydrin in a strong sulphuric acid medium. To obtain the calibration graphs four methods were used: absorbance of reacted cefoxitin against a reagent blank as an analytical signal, first-derivative signal of absorbance against a water blank as an analytical signal, first-derivative signal of absorbance against a reagent blank as an analytical signal and the H-Point Standard Additions Method (HPSAM) by using absorbance increment values as analytical signals. The HPSAM is applied to the determination of cefoxitin i…

Cotton swabs supported in-situ assay for quaternary ammonium compounds residues in effluents and surfaces

2018

Abstract Cellulose paper and cotton swabs have been tested as sampling, reaction and measurement media for quaternary ammonium compounds (QACs) using the reagent Chromo Azurol S in the presence of aluminum cations (CAS-Al). On the basis of the results obtained a new method is proposed for the analysis of QACs in water samples which only entails the successive immersion of swabs into 1 mL of the samples, 1 mL of a solution of CAS-Al for the formation of a ternary blue complex, and 1 mL of water to remove the excess of reagent. The method can be used for the visual on site detection of QACs in effluents, as well as for their quantification within the 3.62–36.2 mg/L range through the direct me…

Innovations in Extractive Phases for In-Tube Solid-Phase Microextraction Coupled to Miniaturized Liquid Chromatography: A Critical Review

2020

Over the past years, a great effort has been devoted to the development of new sorbents that can be used to pack or to coat extractive capillaries for in-tube solid-phase microextraction (IT-SPME). Many of those efforts have been focused on the preparation of capillaries for miniaturized liquid chromatography (LC) due to the reduced availability of capillary columns with appropriate dimensions for this kind of system. Moreover, many of the extractive capillaries that have been used for IT-SPME so far are segments of open columns from the gas chromatography (GC) field, but the phase nature and dimensions are very limited. In particular, polar compounds barely interact with stationary GC phas…

Multivariate standardisation for non-linear calibration range in the chemiluminescence determination of chromium.

2006

Multivariate standardisation is proposed for the successful chemiluminescence determination of chromium based on luminol-hydrogen peroxide reaction. In an extended concentration range, non-linear calibration model is needed. The studied instrumental situations were different detection cells, instruments, assemblies, time and their possible combinations. Chemiluminescence kinetic registers have been transferred using piecewise direct standardisation (PDS) method. The optimisation of transfer parameters has been carried out based on the prediction residual error criteria. Non-linear principal component regression (NL-PCR) and non-linear partial least square regression (NL-PLS) were chosen for…

An evaluation of solid phase microextraction for aliphatic amines using derivatization with 9-fluorenylmethyl chloroformate and liquid chromatography

2005

The reliability of SPME combined with a chemical reaction for the analysis of short-chain aliphatic amines by liquid chromatography has been investigated. Different options to couple SPME and derivatization have been tested and compared: (i) derivatization of the analytes in solution followed by the extraction of the derivatives, (ii) extraction of the analytes and subsequent derivatization by immersing the SPME fibre onto a solution of the reagent, and (iii) extraction/derivatization of the analytes using fibres previously coated with the reagent. Methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) have been selected as a model of primary, secondary and tertiary amines, respecti…

In tube-solid phase microextraction-nano liquid chromatography: Application to the determination of intact and degraded polar triazines in waters and…

2017

Abstract In-tube solid-phase microextraction (IT-SPME) coupled to miniaturized liquid chromatography (LC) techniques are attractive mainly due to the column efficiency improvement, sensitivity enhancement and reduction of solvent consumption. In addition, the nanomaterials based sorbents can play a key role in the improvement of the extraction efficiency taking into account their interesting physical and chemical properties. Thus, in this work the performance of IT-SPME coupled to nano LC (NanoLC) has been compared with the performance of IT-SPME coupled to capillary LC (CapLC) with similar configurations for the determination of polar triazines including their degradation products. In both…

New silica based adsorbent material from rice straw and its in-flow application to nitrate reduction in waters: Process sustainability and scale-up p…

2021

Abstract This paper shows a particular example to move to a sustainable circular economical process from valorization of rice straw ashes by developing a green synthesis for obtaining a useful sub-product. This strategy can palliate negative effects of the agriculture waste practices on the environment and also the obtained silica reduced nitrate content in waters. It is demonstrated that the silica synthesis developed at lab was scalable more than a hundred times with good results. Adsorption studies of nitrate in standards and real well waters at lab scale and scaling-up provided similar results. Adsorption values near to 15 mg/g for nitrate standards and 8.5 mg/g for well water were obta…

Capillary Liquid Chromatography for the Determination of Terpenes in Botanical Dietary Supplements

2021

Dietary supplements of botanical origin are increasingly consumed due to their content of plant constituents with potential benefits on health and wellness. Among those constituents, terpenes are gaining attention because of their diverse biological activities (anti-inflammatory, antibacterial, geroprotective, and others). While most of the existing analytical methods have focused on establishing the terpenic fingerprint of some plants, typically by gas chromatography, methods capable of quantifying representative terpenes in herbal preparations and dietary supplements with combined high sensitivity and precision, simplicity, and high throughput are still necessary. In this study, we have e…

FI automatic method for the determination of copper(II) based on coproporphyrin I-Cu(II)/TCPO/H(2)O(2) chemiluminescence reaction for the screening o…

2004

Abstract In this paper, an automatic method for the screening of water samples containing Cu(II) was proposed, based on peryoxalate chemiluminescence reaction using coproporphyrin I as fluorophor compound to provide selectivity and a simple flow injection (FI) chemiluminescence detector (CLD). FI system conditions were chosen in order to distinguish samples over or under legislation limit established (50 μg l−1) with high reliability. The detection limit found was 9 μg l−1 and the linear dynamic range was 15–125 μg l−1 of Cu(II). Repeatibility and reproducibility studies gave good precision and accuracy with recovery near 100%. Under these conditions, the method resulted selective and only …

NQS-Doped PDMS Solid Sensor: From Water Matrix to Urine Enzymatic Application

2021

The development of in situ analytical devices has gained outstanding scientific interest. A solid sensing membrane composed of 1,2-naphthoquinone-4-sulfonate (NQS) derivatizing reagent embedded into a polymeric polydimethylsiloxane (PDMS) composite was proposed for in situ ammonium (NH4+) and urea (NH2CONH2) analysis in water and urine samples, respectively. Satisfactory strategies were also applied for urease-catalyzed hydrolysis of urea, either in solution or glass-supported urease immobilization. Using diffuse reflectance measurements combined with digital image processing of color intensity (RGB coordinates), qualitative and quantitative analyte detection was assessed after the colorime…

Selective and sentivive method based on capillary liquid chromatography with in-tube solid phase microextraction for determination of monochloramine …

2015

Abstract Due to the difficulties of working with chloramines, a critical examination of monochloramine standard preparation has been performed in order to select the best synthesis conditions. The analyte has been determined by in-tube solid phase extraction coupled to capillary liquid chromatography with UV detection (IT-SPME Capillary LC DAD). Potential factors affecting the response of monochloramine such as the pH of mobile phase and the volume of sample processed by IT-SPME Capillary LC DAD have been investigated and optimized. According to the results of the study, 0.1 mL or 4.0 mL of sample at neutral pH were loaded in the chromatographic system. A sensitive and selective method has …

Ionic-liquid doped polymeric composite as passive colorimetric sensor for meat freshness as a use case.

2020

Abstract A composite membrane containing 1,2-naphthoquinone-4-sulfonic acid sodium salt (NQS) embedded in an ionic liquid (IL)- polydimethylsiloxane (PDMS)- tetraethyl orthosilicate (TEOS)- SiO2 nanoparticles (NPs) polymeric matrix is proposed. The selected IL was 1-methyl-3-octylimidazolium hexafluorophosphate (OMIM PF6). It is demonstrated that ILs chemical additives of PDMS influenced the sol-gel porosity. The sensor analytical performance for ammonia atmospheres has been tested as a function of sampling time (between 0.5 and 312 h), temperature (25 °C and 4 °C) and sampling volume (between 2L and 22 mL) by means of diffuse reflectance measurements and sensor photos, which can be registe…

Improving analysis of apolar organic compounds by the use of a capillary titania-based column: Application to the direct determination of faecal ster…

2010

This article reports a new procedure for the direct determination of faecal sterols coprostanol and cholesterol in wastewater samples as tracers of human sewage contamination. The method combines in-tube solid-phase microextraction (IT-SPME) for analyte enrichment and capillary liquid chromatography (LC) for separation with diode array detection for identification and quantification. A titania-based polymeric capillary column and a conventional octadecyl silica (ODS) capillary column were evaluated and compared for their ability to separate the analytes. The titania-based column allowed the separation of the analytes in much shorter chromatographic times and with better chromatographic prof…

Improving detection limits for organotin compounds in several matrix water samples by derivatization-headspace-solid-phase microextraction and GC-MS.

2010

Triethyltin, tributyltin, diphenyltin and triphenyltin were selected as model compounds. The method is based on in situ ethylation and simultaneous headspace-solid-phase microextraction (HS-SPME) and gas chromatographic-mass spectrometry analysis (GC-MS). The extraction procedure was optimized studying some variables such as reaction time, salinity, sample volume and headspace volume. SPME-GC-MS and SPME-GC-FID techniques were compared; quality assurance parameters such as sensitivity, selectivity and precision were established. The proposed procedure showed limits of detection between 0.025 and 1 ng/L. The linearity was in the 0.025-5000 ng/L range. The precision expressed as relative stan…

Automated high-performance liquid chromatographic determination of amphetamine in biological fluids using column-switching and on-column derivatizati…

1999

A rapid and simple liquid-chromatographic method has been developed for on-line quantification of amphetamine in biological fluids. Untreated samples (20 μL) are injected directly into the chromatographic system and purified on a 20 mm×2.1 mm i.d. pre-column packed with 30 μm Hypersil C18 stationary phase. After clean-up the analyte is transferred to the analytical column (125 mm×4 mm i.d., 5 μm LiChrospher 100 RP18) for derivatization and separation using a mixture of acetonitrile and the derivatization reagent (o-phthaldialdehyde andN-acetyl-L-cysteine) as the mobile phase. The experimental conditions for on-line derivatization and resolution of the amphetamine have been optimized, and th…

Automatic in-tube SPME and fast liquid chromatography: A cost-effective method for the estimation of dibuthyl and di-2-ethylhexyl phthalates in envir…

2007

A 80-cm length commercially available capillary coated with 95% polydimethylsiloxane and 5% polydiphenylsiloxane (TBR-5) was employed to carry out on-line extraction and preconcentration of dibuthyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) in the chromatographic system. The coated capillary was placed between the sample injection loop and the injection needle of an autosampler. Variables affecting the automatic in-tube solid-phase microextraction (SPME) were optimized. A Genesis C(18) (5 cm x 4.6 mm i.d., 4 microm particle size) was employed as analytical column. The achieved limits of detection by use of diode array detection were 1 and 2.5 microg L(-1), respectively. The propo…

Combining high performance thin layer chromatography with minispectrometer-fiber optic probe-coupled to smartphone for in place analysis: Lactose qua…

2021

ABSTRACT An in place colorimetric method has been proposed for estimation of the quantity of lactose in several matrix (milk, water effluents and surfaces). Analyzing the amount of this carbohydrate it can be control the product, the cleanliness of the parts of the dairy companies and it can avoid contamination of milk products produced there. This method combines the use of HPTLC for sugars separation with novel analytical devices as minispectrophotometer with fiber optic coupled to a smartphone. In order to measure the lactose a colorimetric reaction has been used. Variable volumes of samples or stock solutions were deposited in nano-silica gel layer, a mobile phase of acetonitrile:water:…

New Calibration Model: Combining Integrated Calibration Method and H-point Standard Addition Method to Detect and Avoid Interference Effects

2018

A new calibration methodology based on the combination of integrated calibration method (ICM) and the H-point standard addition method (HPSAM) is presented. It allows the diagnosis and correction o...

A capillary liquid chromatography method for benzalkonium chloride determination as a component or contaminant in mixtures of biocides

2015

A method for quantifying benzalkonium chloride (BAK), an alkyl dimethyl benzyl ammonium compound, in several biocides formulations is proposed. A tertiary amine like N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine (TA) and a straight-chain alkyl ammonium compound like trimethyl-tetradecyl ammonium chloride (TMTDAC), have been employed as trade surfactants besides BAK. Two capillary analytical columns with different polarities are tested: inertsil CN-3 capillary column (150mm×0.5mm i.d., 3μm particle diameter) and a non endcapped Zorbax C18 capillary column (35mm×0.5mm i.d., 5μm particle diameter). This latter column provided the best separation of the BAK homologues in less than 12min using …

Overview of the three multicriteria approaches applied to a global assessment of analytical methods

2020

Abstract Critical and global evaluation of analytical methods should be one of the primary goals in analytical chemistry. A holistic approach, however, requires a look at the varied features: commonly discussed validation criteria, often underrated practical and economic aspects, and typically overlooked compliance with the principles of green analytical chemistry. Carrying out such an assessment in a critical and transparent way is extremely difficult without special tools. The purpose of this work is to discuss and compare the three different approaches that seem to be potential candidates: multi-criteria decision analysis methods (MCDA), HEXAGON, and RGB model. The basic principles of ea…

Preconcentration of emerging contaminants in environmental water samples by using silica supported Fe3O4 magnetic nanoparticles for improving mass de…

2011

A magnetic material based on Fe(3)O(4) magnetic nanoparticles incorporated in a silica matrix by using a sol-gel procedure has been used to extract and preconcentrate emerging contaminants such as acetylsalicylic acid, acetaminophen, diclofenac and ibuprofen from environmental water samples prior to the analysis with Capillary LC-MS. The use of the proposed silica supported Fe(3)O(4) magnetic nanoparticles enables surfactant free extracts for the analysis with MS detection without interferences in the ionisation step. Under the optimum conditions, we demonstrated the reusability of the magnetic sorbent material during 20 uses without loss in the extraction efficiency. In addition, no cleanu…

Guidelines for alkylphenols estimation as alkylphenol polyethoxylates pollution indicator in wastewater treatment plant effluents

2013

A solid-phase microextraction coupled with a gas chromatography-mass spectrometry method has been developed for the estimation of technical nonylphenol in the presence of other endocrine disruptors, belonging to different chemical families. The profile of the technical nonylphenol found in real samples was tested, and, given that it was similar to that provided for the standard used, reliable results were obtainable. Endocrine disruptors such as 4-n-nonylphenol, bisphenol A and 4-tert-octylphenol were simultaneously analysed. The best conditions achieved enabled the analysis of all analytes using a sample volume of 15 mL or even only 300 μL. Using such a low sample volume reduced the filtra…

High-performance liquid chromatographic determination of spironolactone and its major metabolite canrenone in urine using ultraviolet detection and c…

1994

A rapid and simple column liquid chromatographic method involving a column-switching system for the determination of spironolactone and its main metabolite canrenone in urine is described. Purification and concentration was performed using an Hypersil ODS-C18, 30 microns (20 x 2.1 mm I.D.) pre-column. The most polar urinary compounds were removed by washing the pre-column with water, and the analytes were subsequently switched to a LiChrospher RP C18, 5 microns (125 x 4 mm I.D.) analytical column and separated by means of an acetonitrile-water mobile-phase. Under the proposed conditions, the extraction efficiency was approximately 100% over the 0.5-10.0 micrograms/ml concentration range. Th…

Off-line dansylation of amines using C18 solid-phase packings: study of the fluorescence and chemiluminescence detection by post-column derivatizatio…

1999

Abstract Dansylation of amines (primaries and secondaries) using C18 solid-phase supports is described. The time of analysis and the handing sample have been markedly improved with respect to those required for solution dansylation. The dansylated amine derivates were injected onto the liquid chromatography system and fluorescence detected. The sensitivity and selectivity is better than the other dansylation procedures described in the literature and also better than other derivatization reagents such 1,2-napthoquinone 4-sulfonate (NQS) or 3,5-dinitrobenzoyl chloride (3,5-DNB). Dansyl compounds can also form chemiluminescent derivatives, therefore a post-column derivatization procedure with…

Quantitative Analysis of Terpenic Compounds in Microsamples of Resins by Capillary Liquid Chromatography

2019

A method has been developed for the separation and quantification of terpenic compounds typically used as markers in the chemical characterization of resins based on capillary liquid chromatography coupled to UV detection. The sample treatment, separation and detection conditions have been optimized in order to analyze compounds of different polarities and volatilities in a single chromatographic run. The monoterpene limonene and the triterpenes lupeol, lupenone, &beta

Analysis of Contact Traces of Cannabis by In-Tube Solid-Phase Microextraction Coupled to Nanoliquid Chromatography

2018

Because of its inherent qualities, in-tube solid-phase microextraction (IT-SPME) coupled on-line to nanoliquid chromatography (nanoLC) can be a very powerful tool to address the new challenges of analytical laboratories such as the analysis of traces of complex samples. This is the case of the detection of contact traces of drugs, especially cannabis. The main difficulties encountered in the analysis of traces of cannabis plants on surfaces are the low amount of sample available (typically &lt

Determination of meropenem in endotracheal tubes by in-tube solid phase microextraction coupled to capillary liquid chromatography with diode array d…

2017

Meropenem is a widely used antimicrobial for the treatment of infections associated with the use of invasive medical devices in intensive care unit patients. These treatments are not always effective, in fact, in-vitro studies have demonstrated the difficulty of antimicrobials to penetrate into the biofilm, however in-vivo studies of the effect of these compounds is a trend, mostly because of the complexity of pulmonary samples extracted from ETTs. Therefore, the objective of this study was to evaluate in-tube solid phase microextraction (in-tube SPME) coupled to capillary liquid chromatography (CapLC) with DAD to determine meropenem in Errs in order to estimate the penetration capability i…

Trends in Online Intube Solid Phase Microextraction

2017

Cleaning sorbents used in matrix solid-phase dispersion with sonication: Application to the estimation of polycyclic aromatic hydrocarbons at ng/g le…

2012

This study shows that ultrasonic assisted extraction is a good practise for removing impurities from sorbents used for matrix-solid phase dispersion (MSPD). A previous washing of the sorbent with an organic solvent or mixture of solvents eliminates part of the interferences, but this treatment is not enough for the quantification of PAHs at ng/g levels. It is demonstrated that the determination of traces of polycyclic aromatic hydrocarbons (PAHs) in solid samples processed by matrix-solid phase dispersion (MSPD) may be severely affected by the presence of sorbent impurities. Different extraction solvents and sonication conditions have been tested, and on the basis of the results obtained a …

A solid device based on doped hybrid composites for controlling the dosage of the biocide N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine in industria…

2015

A colorimetric composite device is proposed to determine the widely used biocide N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine (ADP).This sensing device is based on a film of 1,2-Naphthoquinone-4-sulfonate (NQS) embedded into polydimethylsiloxane-tetraethylortosilicate-SiO2 nanoparticles composite (PDMS-TEOS-SiO2NPs). Semiquantitative analysis can be performed by visual inspection. Digitalized image or diffuse reflectance (DR) measurements can be carried out for quantitative analysis. Satisfactory detection limit (0.018%, w/v) and relative standard deviations <12% were achieved. The proposed device has been applied for the determination of ADP in detergent industrial formulations with reco…

On-line trace enrichment for the determination of ethacrynic acid in urine by liquid chromatography and column-switching

1993

Abstract A chromatographic method based on liquid chromatography (LC) using column-switching for the determination of ethacrynic acid in urine samples, is described. The proposed system uses a Hypersil ODS-C18, 30 μm (20 mm × 2.1 mm i.d.) pre-column for the pre-concentration and separation of ethacrynic acid from the biological matrix. Polar urinary compounds are removed by flushing the pre-column with purified water, and the enriched analyte is then switched in back-flush mode onto an HP-LiChrospher RP C18, 5 μm (125 × 4 mm i.d.) analytical column, where it is chromatographed using an acetonitrile-acetate buffer gradient elution. The UV detector was set at 275 nm. The recovery of drug was …

Automated on-line in-tube solid-phase microextraction-assisted derivatization coupled to liquid chromatography for quantifying residual dimethylamine…

2008

Abstract A method for the analysis of dimethylamine (DMA) by automated in-tube solid-phase microextraction (IT-SPME)-supported chemical derivatization coupled with high-performance liquid chromatography was developed. Extraction, derivatization and desorption were studied by using a capillary coated with 95% polydimethylsiloxane and 5% polydiphenylsiloxane. Solution derivatization and automated IT-SPME derivatization using 9-fluorenylmethyl chloroformate (FMOC) were compared. The proposed procedure provided adequate linearity, accuracy and precision in the 0.2–2.0 μg/mL concentration interval, and the limit of detection (LOD) was 50 ng/mL. The main advantages of the proposed procedure are: …

Improving the On-Line Extraction of Polar Compounds by IT-SPME with Silica Nanoparticles Modified Phases

2018

In the present work the extraction efficiency of in-tube solid-phase microextraction (IT-SPME) for polar herbicides has been evaluated using extractive capillaries coated with different polymeric sorbents. For this purpose, aqueous solutions of herbicides with a wide range of polarities, including some highly polar compounds (log Kow &lt; 1), have been directly processed by IT-SPME coupled on-line to capillary liquid chromatography with UV-diode array detection. For extraction, commercially available capillary columns coated with polydimethylsiloxane (PDMS) and polyetilenglicol (PEG)-based phases have been used, and the results have been compared with those obtained with a synthesized tetra…

Evaluation and elimination of the blank bias error using the H-point standard additions method (HPSAM) in the simultaneous spectrophotometric determi…

1997

Abstract The aim of this report is to demonstrate the usefulness of the HPSAM in all instances where the determination of two analytes requires the use of an absorbent reagent, particularly when it does not present a constant analytical signal because of its consumption. This problem can be treated as a ternary mixture by the HPSAM method and then, the fundamentals of the method for resolving these kind of mixtures can be applied. The method can calculate the concentration of one species from spectral data at two wavelengths where the two other species present the same absorbance relationship. These wavelength pairs are easily found, and can be selected to give the most precise results. The…

H-Point Curve Isolation Method for Coupled Liquid Chromatography and UV−Visible Spectrophotometry

2000

The H-point curve isolation method (HPCIM) for the detection of unknown interferences in chromatography is proposed. The method allows one to estimate the UV-vis spectra of interfering species in a sample as well as to test the purity of the chromatographic peaks. Besides the detection of the unknown interferences in a sample, this method allows one to calculate the concentration of an analyte in the presence of unknown compounds. To illustrate the reliability of the proposed method, samples of diuretics and amphetamines have been analyzed by normal- and reversed-phase high-performance chromatography.

Comparative Study on the Determination of Cephalexin in its Dosage Forms by Spectrophotometry and HPLC with UV-vis Detection

1997

This paper discusses the spectrophotometric determination of cephalexin as the intact cephalexin or as its acid-induced degradation product. Cephalexin can be determined in the range 1 × 10−5−18 × 10−5M with relative standard deviations of 5-1%. The limits of quantitation and detection were 10−5 and 0.3 × 10−5M, respectively. These procedures were compared with reversed-phase HPLC determination. No interference was observed in the presence of common pharmaceutical adjuvants. The H-point standard additions method was applied in order to correct for the possible presence of the cephalexin precursor, 7-aminocephalosporanic acid; this improves the selectivity of the UV-vis spectrophotometric me…

On-fibre solid-phase microextraction coupled to conventional liquid chromatography versus in-tube solid-phase microextraction coupled to capillary li…

2006

This paper compares the advantages and disadvantages of two different configurations for the extraction of triazines from water samples: (1) on-fibre solid-phase microextraction (SPME) coupled to conventional liquid chromatography (LC); and (2) in-tube SPME coupled to capillary LC. In-tube SPME has been effected either with a packed column or with an open capillary column. A critical evaluation of the main parameters affecting the performance of each method has been carried out in order to select the most suitable approach according to the requirements of the analysis. In the on-fibre SPME configuration the fibre coating was polydimethylsiloxane (PDMS)-divinylbenzene (DVB). The limits of de…

Liquid chromatographic determination of aliphatic amines in water using solid support assisted derivatization with 9-fluorenylmethyl chloroformate

2002

A simple and sensitive method has been developed for the liquid chromatographic determination of short-chain aliphatic amines in water. Analytes are retained in solid-phase extraction (SPE) cartridges, and then derivatized by drawing an aliquot of the fluorogeneic reagent 9-fluorenylmethyl chloroformate (FMOC) through the cartridges. After a certain reaction time the derivatives formed are desorbed with acetonitrile. The collected extracts are then chromatographed on a LiChrospher 100 RP18 125 mm×4 mm i.d., 5 μm, column using an acetonitrile-water gradient. The influence of experimental conditions (SPE material, volume of sample, concentration of FMOC, time of reaction and pH) has been inve…

The generalized H-point standard-additions method to determine analytes present in two different chemical forms in unknown matrix samples. Part II. C…

2000

The generalized H-point standard-additions method (GHPSAM) is used in order to obtain the total Cr(VI) and chromate concentration in water samples whose matrices are completely unknown. Moreover, a new methodology, which is a modification of the GHPSAM, is proposed for the simultaneous determination of the two major chemical forms of Cr(VI) present in the sample. The method is based on the location of spectral intervals where the behaviour of the interferent absorbance can be considered as linear. From these intervals, the analyte concentration free from bias error can be estimated. Spiked samples of dig and harbour water measured in the UV–visible spectral region have been tested to check …

Characterization and Quantitation of Carbon Black Nanomaterials in Polymeric and Biological Aqueous Dispersants by Asymmetrical Flow Field Flow Fract…

2021

Characterization of carbon black (CB) nanomaterials is required in industrial and research areas. Hence, in this study, asymmetrical flow field flow fractionation coupled to UV–vis and DLS detectors in series (AF4-UV–vis-DLS) was studied to evaluate the CB dispersion behavior in polymeric and biological dispersants, given the relevance of these media in practical applications. Under the experimental conditions, the results indicated that polymeric and biological dispersions showed size distributions with hydrodynamic diameters of 404 and 175 nm, respectively, for a particle core diameter of 40 nm. The polymeric dispersant provided lower stability as a function of time than that achieved by …

Development of a polydimethylsiloxane–thymol/nitroprusside composite based sensor involving thymol derivatization for ammonium monitoring in water sa…

2014

This report describes a polydimethylsiloxane (PDMS)-thymol/nitroprusside delivery composite sensor for direct monitoring of ammonium in environmental water samples. The sensor is based on a PDMS support that contains the Berthelot's reaction reagents. To prepare the PDMS-thymol/nitroprusside composite discs, thymol and nitroprusside have been encapsulated in the PDMS matrix, forming a reagent release support which significantly simplifies the analytical measurements, since it avoids the need to prepare derivatizing reagents and sample handling is reduced to the sampling step. When, the PDMS-thymol/nitroprusside composite was introduced in water samples spontaneous release of the chromophore…

New spectrophotometric procedure for determining cefotaxime based on derivatization with 1,2-naphthoquinone-4-sulphonate into solid-phase extraction …

1998

Cefotaxime was derivatised with 1,2-naphthoquinone-4-sulphonate (NQS), extracted into solid-phase cartridges (C18) and detected using a UV-visible detection system. Optimum conditions for this new procedure were: hydrogencarbonate-carbonate buffer, pH 10.5, 5-min reaction time at 25 degrees C and an NQS concentration of 7.1x10(-3) mol l(-1). The accuracy and the precision of the liquid-solid procedure were tested. The procedure was used to measure cefotaxime in pharmaceutical and urine samples. The results obtained were contrasted with those reported for a HPLC method for urine samples. The generalized H-point standard additions method was used to measure cefotaxime in urine samples.

Development of the H-point standard additions method for coupled liquid chromatography and UV-visible spectrophotometry

1992

Abstract This work establishes the fundamentals of the H-point standard additions method for liquid chromatography for the simultaneous analysis of binary mixtures with overlapped chromatographic peaks. The method was compared with the deconvolution method of peak suppression and the second derivative of elution profiles. Different mixtures of diuretics were satisfactorily resolved.

Sensitive determination of ethacrynic acid in urine samples by reversed-phase liquid chromatography with ultraviolet detection using solid-phase extr…

1992

Abstract A rapid method is described for the identification and determination of ethacrynic acid in human urine samples by liquid chromatography with UV detection, the retention time of the analyte being 4.9 min. The samples were previously conditioned using C 18 solid-phase extraction columns and chromatographed on an HP-LiChrospher RP C 18 column (5 μm; 125 mm × 4 mm i.d.) with gradient elution with acetonitrile-acetate buffer (pH 4). The detector was set at 275 nm and furosemide was used as an internal standard. The procedure was applied to the determination of ethacrynic acid at concentrations of 0.01-10 μg ml -1 and the limit of detection was 6 ng ml -1 .

Derivatization of tertiary amphetamines with 9-fluorenylmethyl chloroformate for liquid chromatography: determination of N-methylephedrine.

2000

The fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) was evaluated for the derivatization of tertiary amphetamines prior to liquid chromatographic analysis. Conditions for the derivatization were investigated, including the reaction time, the derivatization reagent concentration and the pH, using N-methylephedrine as a model compound. On the basis of these studies, a method for the quantification of N-methylephedrine is presented. The method involves derivatization with FMOC at ambient temperature and separation of the derivatives formed on a LiChrospher C18, 5 μm, 125 × 4 mm id column using acetonitrile–water gradient elution. The proposed procedure shows good linearity, accuracy…

Advantages of monolithic over particulate columns for multiresidue analysis of organic pollutants by in-tube solid-phase microextraction coupled to c…

2011

Abstract The performance of a monolithic C 18 column (150 mm × 0.2 mm i.d.) for multiresidue organic pollutants analysis by in-tube solid-phase microextraction (IT-SPME)-capillary liquid chromatography has been studied, and the results have been compared with those obtained using a particulate C 18 column (150 mm × 0.5 mm i.d., 5 μm). Chromatographic separation has been carried out under isocratic elution conditions, and for detection and identification of the analytes a UV-diode array detector has been employed. Several compounds of different chemical structure and hydrophobicity have been used as model compounds: simazine, atrazine and terbutylazine (triazines), chlorfenvinphos and chlorp…

Derivatization techniques for automated chromatographic analysis of amphetamine usingo-phthaldialdehyde: A comparative study

2000

The potential of different chromatographic systems for automated, on-line analysis of amphetamine in biological fluids is illustrated. The various systems integrate analyte purification and enrichment, separation, derivatization in different derivatization modes witho-phthaldialdehyde (OPA) and N-acetyl-L-cysteine (NAC), and fluorimetric detection. The reliability of the systems has been tested by analysing urine and plasma samples containing amphetamine in the 0.1–20.0 μg mL−1 range. Pre, on and post-column derivatization strategies are compared in terms of their instrumental requirements, selectivity, sensitivity, linearity and reproducibility.

Minimizing the impact of sample preparation on analytical results: In-tube solid-phase microextraction coupled on-line to nano-liquid chromatography …

2020

The degradation kinetics and residual levels of the sulfonylurea herbicide tribenuron-methyl (TBM) in different environmental waters were studied using in tube-solid phase microextraction (IT-SPME) coupled on-line to nano-liquid chromatography (nanoLC) and UV diode array detection (DAD). This approach combines the high extraction efficiency of IT-SPME using polymeric coatings reinforced with metal oxide nanoparticles and the high sensitivity attainable by nanoLC, making possible the determination of TBM at low ppb levels (limit of detection, 0.25 ppb) without altering the sample matrix. The present study demonstrated that the preservation of the sample properties is essential to ensure accu…

Quantitative study of the capture of silver nanoparticles by several kinds of soils

2018

The capacity of different soils to capture silver nanoparticles (AgNPs) by measuring changes of an AgNP intrinsic property such as the plasmon for the first time, was studied. In-tube solid-phase microextraction (IT-SPME) coupled on-line to capillary liquid chromatography (CapLC) with diode array detection (DAD) was employed for measuring the interactions between soil and in-contact AgNP dispersions. Its achieved LOD 9 pM assures quantitative retention measurements and selectivity for soil lixiviation was suitable. Electronic microscopy was employed for corroborating the entrapped Ag into the soils. Capture % of AgNPs was calculated in compost (>99%), mountain (>99%), orchard (15±1%) and ur…

Establishing the occurrence and profile of polycyclic aromatic hydrocarbons in marine sediments: The eastern Mediterranean coast of Spain as a case s…

2019

Sampling, cost-effective analysis, diagnosis of sources of pollution and assessment of potential toxicological effects were included in the case study. Marine sediments collected from 24 points along the eastern Mediterranean coast of Spain (Comunitat Valenciana region) in 2010, 2011, 2012 and 2015 have been analysed for polycyclic aromatic hydrocarbons. Fluoranthene, pyrene, chrysene, benzo[b]fluoranthene and benzo[a]pyrene were the most found. An analysis of the relative abundance of selected PAHs revealed that petrogenic and mixed petrogenic/pyrogenic sources are predominant in the area. The total concentrations of the target compounds ranged from 14.7 to 615.3 ng/g dry weight. The effec…

Solid glucose biosensor integrated in a multi-well microplate coupled to a camera-based detector: Application to the multiple analysis of human serum…

2018

Abstract In the present work, a biosensor adapted in a 96-well microplate has been coupled with a smartphone-based photometer in order to develop a low-cost colorimetric multi-sample dispositive. The strength of this biosensing system is based on the integration of the biosensor into the 96-well microplate and the use of a smartphone and free image analysis software as a microplate reader. The performance of the proposed biosensor has been demonstrated to determine glucose in several human serum samples. This method is simple, cost-effective, sensitive and selective for the determination of glucose in serum, with detection limits of 1.8 mg/dL and a good linearity over the range 6–88 mg/dL. …

A Colorimetric Membrane-Based Sensor with Improved Selectivity towards Amphetamine

2021

Due to their simplicity, speed and low cost, chemical spot tests are increasingly demanded for the presumptive identification of illicit drugs in a variety of contexts such as point-of-care assistance or prosecution of drug trafficking. However, most of the colorimetric reactions used in these tests are, at best, drug class selective. Therefore, the development of tests based on chemical reactions with improved discrimination power is of great interest. In this work, we propose a new colorimetric assay for amphetamine (AMP) based on its reaction with solutions of alkaline gold bromide to form an insoluble yellow–orange derivative. The resulting suspensions are then filtered onto nylon membr…

Development of the H-point standard additions method for analyte determinations in unknown matrix

1993

Abstract The development of the H-point standard additions method is proposed in order to obtain the unbiased analyte concentration when the matrix of the sample is completely unknown. A spectral region where the interferent behaviour can be considered linear at three wavelengths must be chosen. The method uses the analytical signal data at these three wavelengths, usually situated in the maxima region of the analyte. Two procedures are proposed in order to know and to locate this behaviour for the unknown interferent. Several binary and ternary mixtures of phenol, 4-chlorophenol and 4-chloro-3-methylphenol as representative examples have been assayed, with accurate (less than 3% relative e…

Colorimetic biosensing dispositive based on reagentless hybrid biocomposite: Application to hydrogen peroxide determination

2016

Abstract An efficient approach to enhance the performance of colorimetric biosensors has been developed. The biosensor is based on the co-immobilization of the reagent 3,3′,5,5′-teramethylbencidine (TMB) and the enzyme horseradish peroxidase (HRP) in a PDMS-TEOS-SiO2NPs support. The HRP, in presence of H2O2, catalyzes the oxidation of TMB, producing a blue color. The generated biosensor, doped with the substrate (TMB) and the enzyme (HRP) (entrapped or adsorbed), has been used to determine H2O2 in real samples. Firstly, the immobilization of TMB and HRP in the composite has been studied in order to find the best suitable configuration. The kinetic parameters Vmax (maximum reaction rate) and…

Sensitive determination of methylenedioxylated amphetamines by liquid chromatography.

2001

Different strategies for the liquid chromatographic determination of methylenedioxylated amphetamines were evaluated: separation and detection of underivatized analytes by (i) UV or (ii) fluorescence, (iii) derivatization with 3,5-dinitrobenzoyl chloride followed by separation and UV detection of the derivatives formed and (iv) derivatization with 9-fluorenylmethyl chloroformate (FMOC) and subsequent separation and fluorimetric detection of the derivatives. The compounds tested were 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyethylamphetamine (MDE). On the basis of these studies, a new procedure for the chromatographic determination of…

Aqueous Dilution of Noble NPs Bulk Dispersions: Modeling Instability due to Dissolution by AF4 and Stablishing Considerations for Plasmonic Assays

2020

Among different nanomaterials, gold and silver nanoparticles (AuNPs and AgNPs) have become useful tools for a wide variety of applications in general, and particularly for plasmonic assays. Particle size and stability analysis are key elements for their practical applications since the NPs properties depend on these parameters. Hence, in the present work, asymmetrical flow field flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, has been evaluated for stability studies of citrate-capped AuNPs and AgNPs aqueous dispersions. First, experimental parameters, such as mobile phase or cross-flow rate were optimized. Sodium azide to pH 7 for AuNPs and…

Zein as biodegradable material for effective delivery of alkaline phosphatase and substrates in biokits and biosensors

2016

A biodegradable material, zein, is proposed as a reagent delivery platform for biokits and biosensors based on alkaline phosphatase (ALP) activity/inhibition in the presence of phosphatase substrates. The immobilization and release of both the substrate and/or the active ALP, in a biodegradable and low-cost material such as zein, a prolamin from maize, and in combination with glycerol as plasticizer have been investigated. Three zein-based devices are proposed for several applications: (1) inorganic phosphorus estimation in water of different sources (river, lake, coastal water and tap water) with a detection limit of 0.2mg/L - compared to at least 1mg/L required by legislation, (2) estimat…

The H-point and generalized H-point standard additions methods for flow injection procedures.

1997

This paper establishes the fundamentals of the H-point standard additions method (HPSAM) and generalized H-point standard additions method (GHPSAM) in the flow injection technique. Two kinds of analytical signals can be employed, FIA peaks and spectra. Different analytical problems have been studied: determinations of one analyte in the presence or absence of matrix effect when different blank features are present, and determination of two analytes in the presence of blank bias error affecting the development of one of them. The determination of chloride with mercury thiocyanate which presents a matrix effect, and the determinations of calcium and/or magnesium with arsenazo III are examined…

Liquid Chromatographic Analysis of Amphetamine and Related Compounds in Urine Using Solid-Phase Extraction and 3,5-Dinitrobenzoyl Chloride for Deriva…

1997

A chromatographic method for the analysis of amphetamine and related compounds in urine using 3,5-dinitrobenzoyl chloride (3,5-DNB) as a labeling reagent is presented. This assay is based on the employment of solid-phase extraction (SPE) cartridges for sample cleanup and derivatization. Experimental conditions are optimized for the simultaneous derivatization of ephedrine, norephedrine, pseudoephedrine, beta-phenylethylamine, amphetamine, methamphetamine, and 3-phenylpropylamine. The derivatives formed are separated in a LiChrospher 1000 RP18 (125 x 4-mm i.d., 5-microns film thickness) analytical column using a water-acetonitrile gradient elution and detected at 254 nm. Derivatization in C1…

Separation of the enantiomers of primary and secondary amphetamines by liquid chromatography after derivatization with (−)-1-(9-fluorenyl)ethyl chlor…

2003

The chiral reagent (−)-1-(9-fluorenyl)ethyl chloroformate (FLEC) has been evaluated for the enantioselective analysis of amphetamines by liquid chromatography. For separation of the FLEC diastereomers conventional reversed-phase conditions were used. The conditions affording the best enantiomeric resolution and sensitivity were determined for amphetamine, methamphetamine, ephedrine, pseudoephedrine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDE). All the amphetamines assayed could be separated with resolution factors ranging from 0.91 to 1.92. Although FLEC is typically used as a fluorogenic reagent, it was shown t…

Quantifying both ammonium and proline in wines and beer by using a PDMS composite for sensoring.

2019

Abstract Two of the reagents involved in the Berthelot's reaction, thymol and nitroprusside, were embedded in a PDMS composite in order to apply this assay to determine ammonium and proline, in wine and beers. Safety, portability, rapidity, cost-effectiveness and simplicity of the assay were improved. For the proline determination, a modified Berthelot's reaction, which included a ring cleavage of proline, was optimized. The accuracy of the assay was tested. The limits of detection for ammonium was 0.12 µg mL−1 and for proline was in the range from 0.7 to 4.1 µg mL−1, depending on the kind of wine (white, red, or sweet), for beer the LOD was 6 µg mL−1. The precision achieved was slower than…

Exploring hand-portable nano-liquid chromatography for in place water analysis: Determination of trimethylxanthines as a use case.

2020

Abstract Analytical performance and optimization of figures of merit of a portable nano liquid chromatograph (NanoLC) with UV detection at 255 nm have been established for in place analysis. Methylxanthines: caffeine, theophylline and theobromine were selected as target analytes. A fast lab method based on IT-SPME coupled on line with capillary liquid chromatograph (CapLC) with diode array detection (DAD) was employed for comparative studies. IT-SPME and solid phase extraction were coupled off-line to NanoLC for improving instrumental parameters, mainly detection capacity and selectivity. IT-SPME or SPE/portable NanoLC based methods were superior in terms of chromatographic resolution and o…

Analyte estimation using the generalized H-point standard additions method and a new methodology for locating linear spectral intervals for unknown i…

1998

An improvement in the way to locate linear spectral intervals for unknown interferents which overlap the analyte signal in UV–visible spectrophotometry is offered as an alternative to the method previously described by Campins-Falco et al. (Anal. Chim. Acta, 302, 323 (1995)). In that report, quotients of the second-derivative spectra of the sample and analyte were used. The new method improves on the old one by using first- instead of second-derivative data, thus eliminating the possible divisions by zero (inflection points for the analyte) obtained in the previous procedure. The linear intervals are now obtained by plotting for each wavelength the differences in first-derivative data betwe…

A method for the determination of dimethylamine in air by collection on solid support sorbent with subsequent derivatization and spectrophotometric a…

2005

A new method for dimethylamine determination in air is reported. The proposed assay is based on the employment of C18-packed solid phase extraction cartridges for sampling. The retained amine is then derivatized inside the cartridges with the reagent 1,2-naphthoquinone-4-sulfonate. By observing the coloured area of the cartridge, a semiquantitative estimation of the amine can be made. It was also possible to distinguish between primary and secondary amines by visual inspection. Quantitative tests entailed desorption from the cartridges of the derivatives formed, and measurement of the absorbance of the collected extracts. The selected conditions were applied to quantify dimethylamine up to …

A passive solid sensor for in-situ colorimetric estimation of the presence of ketamine in illicit drug samples

2017

Abstract A colorimetric sensor has been developed for the presumptive detection of ketamine in illicit drug samples. The sensor has been prepared by immobilized the reagent Co(SCN) 2 into polydimethylsiloxane (PDMS). When exposed to solutions of ketamine at a basic pH, the sensor color changes from brown to blue-purple due to the diffusion of the analyte molecules to the polymeric matrix and subsequent interaction with the reagent particles. The sensor enables the visual identification of amounts of drug as low as 30 μg in a few minutes. Quantification of ketamine is also possible through the measurement of the absorbance in diffuse reflectance mode. Under the proposed conditions, linear re…

A cost-effective method for estimating di(2-ethylhexyl)phthalate in coastal sediments.

2013

This study describes the development of a new method for the analysis of di(2-ethylhexyl)phthalate (DEHP) using 0.1-0.3 g of sediment sample, based on matrix solid phase dispersion (MSPD) using C18 as dispersant phase (0.4 g) and acetonitrile-water as eluting solvent (3.4 mL 1:3.25, v/v). No evaporation step is required. 3 mL of extracts were processed on-line by in-tube solid phase microextraction (IT-SPME) coupled to capillary liquid chromatography (CapLC) and diode array detector (DAD). A short analytical column Zorbax SB C18 (35×0.5 mm, 5 μm) provided suitable results. FTIR-ATR was employed for characterizing sediment samples and MSPD procedure. The total analysis time was less than 20 …

Urine polyamines determination using dansyl chloride derivatization in solid-phase extraction cartridges and HPLC

1999

The derivatization of biogenic amines such as putrescine, cadaverine, spermidine and spermine with dansyl chloride in solid phase extraction cartridges is described. Different types of filling materials were tested in order to have the highest retention of the different analytes. The best results were obtained by using C18 cartridges. The optimal conditions were: amine solution buffered at pH 12, 2 mM dansyl chloride (acetone-bicarbonate solution 20 mM (pH 9-9.5), 2 + 3 v/v) as reagent concentration, room temperature and 30 min reaction time. The developed procedure was applied to the determination of these polyamines in urine samples from healthy controls and cancer patients using HPLC wit…

Influence of water sample storage protocols in chemiluminescence detection of trace elements.

2002

This paper shows the influence of different sample storage protocols, on the chemiluminescence signal of some metal ions. The storage protocols studied were: acid addition (HCl or HNO(3)) and no reagent addition to filtered and refrigerated (T=4 degrees C) samples. Light emission was produced for the chemiluminescence reaction between luminol and hydrogen peroxide in buffer carbonate conditions (pH 10.8) catalysed by Cr(III), Co(II) and Cu(II). Batch and/or flow modes in different conditions were tested. Fe(II), Fe(III), Ni(II) and Mn(II) did not give chemiluminescence in the studied conditions. A parallel study of sensitivity and selectivity was performed. Then the presence or absence of t…

The impact of a disused mine on uranium transport in the River Fal, South West England.

2004

Unfiltered and filtered (0.45 and 0.2 microm) water samples and sediment samples (sieved to180 microm and 180-1000 microm) were collected along an approximately 15 km transect of the River Fal, Cornwall, UK, to examine the impact of the disused South Terras uranium mine on the uranium concentrations of the river water and underlying sediments. The uranium concentration of the water samples fluctuated along the river, with the 0.45 microm filtered water showing the largest, seven-fold, difference between minimum (0.19 microg L(-1)) and maximum (1.34 microg L(-1)) concentrations. The historical uranium mine and spoil heaps were not a significant source of uranium to the river water, as water …

Microextraction with phases containing nanoparticles.

2015

In this article, the state of the art of microextraction techniques that involve nanoparticles or nanomaterials (NPs) is reviewed, with special emphasis on the applications described in the biomedical field. The uses and advantages of the different types of NPs such as carbon nanotubes (either single- and multi-walled) and other carbon-based materials, metallic NPs, including gold, silver and magnetic NPs, and silica NPs are summarized. The main strategies used to modify the selectivity, extractive capacity and/or the stability of NPs through a chemical reaction are also reviewed. The potential advantages of NPs in different forms of off-line and on-line microextraction are discussed, and …

Chromatographic separation of chlorthalidone enantiomers using β-cyclodextrins as chiral additives

2000

Different beta-cyclodextrins have been tested as chiral additives in the mobile phase for the chromatographic analysis of chlorthalidone enantiomers in a C18 LiChrospher (125 x 4 mm I.D.) column. The effect on enantioresolution of different parameters was studied: composition of the mobile phase (percentage of organic solvent, type of buffer and pH), mobile phase flow-rate, and type and concentration of beta-cyclodextrin. A 25:75 mixture of methanol and 0.1 M phosphate buffer, pH 4, containing 2% triethylamine (v/v), and 12.5 mM beta-cyclodextrin, at a flow-rate of 0.8 ml/min, was found to be the best option for the resolution of chlorthalidone enantiomers. Under such conditions, linear cal…

Determination of aliphatic amines in water by liquid chromatography using solid-phase extraction cartridges for preconcentration and derivatization

2001

Bond Elut C18 solid-phase extraction cartridges were used for preconcentration and pre-column derivatization with 3,5-dinitrobenzoyl chloride (DNB) of aliphatic amines in water. Conditions for analyte preconcentration and derivatization (including the volume of sample, concentration of reagent, time of reaction and pH) were investigated, using ethylamine, isopropylamine and dimethylamine as model compounds. On the basis of these studies, a rapid and sensitive method for the determination of aliphatic amines in water is presented. The analytes are retained and purified on the cartridges and then derivatized and desorbed by drawing in succession the DNB solution and acetonitrile. The collecte…

An in-tube SPME device for the selective determination of chlorophyll a in aquatic systems.

2010

We report a new device for the estimation of the content of chlorophyll a pigment in water samples as an indicator of water quality. The extraction of the pigment from water was also optimized. 10 mL of water was filtered through a nylon filter (45m pore size and 13 mm of diameter), after the chlorophylls were dissolved by immersing the filter in 1 mL of a low non-hazardous solvent as ethanol. An in-valve in-tube SPME device coupled to capillary liquid chromatography with diode array detection was designed. A capillary column of 70 cm in length (0.32 mm i.d. coated with 5% diphenyl–95% polydimethylsiloxane, 3m coating thickness) was used as the loop of the injection valve for preconcentrati…

A microanalytical method for ammonium and short-chain primary aliphatic amines using precolumn derivatization and capillary liquid chromatography.

2007

Abstract A new microscale method is presented for the determination of ammonium and primary short-chain aliphatic amines (methylamine, ethylamine, propylamine, n -butylamine and n -pentylamine) in water. The assay uses precolumn derivatization with the reagent o -phthaldialdehyde (OPA) in combination with the thiol N -acetyl- l -cysteine (NAC), and capillary liquid chromatography with UV detection at 330 nm. The described method is very simple and rapid as no preconcentration of the analytes is necessary, and the volume of sample required is only 0.1 mL. Under the proposed conditions good linearity has been obtained up to a concentration of the analytes of 10.0 mg L −1 , the limits of detec…

Selective determination of ammonium in water based on HPLC and chemiluminescence detection

2005

Abstract A selective and sensitive method has been developed for liquid chromatographic determination of ammonium in water samples. The analyte is derivatized with Dansyl Chloride prior to injection into HPLC. Optimal solution derivatization conditions have been established. The dansyl derivative is separated with the aid of a chromatographic column and post-column mixed with peroxyoxalate (TCPO) and H 2 O 2 in order to perform chemiluminescence detection. The detection limit achieved is 8 μg/L and linear response from 0.027 to 0.750 mg/L of ammonium was obtained. Ammonium ion was determined within 2.4 min under optimum chromatographic conditions. The method is fast, and near 10 derivatized…

A microscale Kjeldahl nitrogen determination for environmental waters.

2008

A microscale Kjeldahl system has been designed which has been homemade reduced. The digestor unit of a macroKjeldahl system and a modified glassware microdistillation unit have been used. The optimal conditions for digestion and distillation have been established for ammonium and methylamine as model compound of organic amino nitrogen. The optimised procedure has been applied to the determination of Kjeldahl nitrogen in water samples. Recoveries near 100% and good precision have been achieved. This procedure combines nitrogen miniaturized system and the use of a selective ion electrode for ammonia detection. The analysis time was reduced 4.8 times and the analysis cost 6.6 times compared wi…

More about sampling and estimation of mercaptans in air samples

2013

[EN] Several strategies have been developed for sampling and determination of volatile thiols. The selectivity and sensitivity of the proposed methodologies are achieved by using a specific derivatizing reagent. The different procedures assayed are based on air sampling followed by derivatization of the analytes with OPA and isoleucine in alkaline solution. The derivatization products are separated and determined by liquid chromatography and fluorescence detection. To start, the derivatization conditions and stability of the derivates have been studied in order to establish the storage conditions. In general, the strategies studied consisted on trapping and detivatization the thiol compound…

Principal component analysis for the selection of variables in the application of the H-point and generalised H-point standard addition method

2000

The present paper deals with the selection of variables for the H-point and generalised H-point standard additions methods (HPSAM and GHPSAM, respectively). Both methods are applied for the resolution of spectroscopic interfered signals in the UV-vis range. The HPSAM is a suitable method for the resolution of binary and ternary mixtures when the interferent is known. The GHPSAM is applied for the resolution of samples that contain unknown interferents. In this paper, a method based on the study of a principal components analysis (PCA) for the selection of variables for the HPSAM and GHPSAM is proposed. The PCA results show the isolation of the analyte signal from the sample signal, achieved…

New results in ancient Maya rituals researches: The study of human painted bones fragments from Calakmul archaeological site (Mexico)

2020

Abstract The funeral chambers of the ancient city of Calakmul (Mexico) and the individuals who were buried in them have brought in recent decades new knowledge about the beliefs and funeral customs of the pre-Hispanic Maya. Tombs and bodies were prepared as part of the rituals that should favor the return of ch'ulel to the Underworld, known as Xibalba by the ancient Maya. The ch'ulel is one of the two anemic entities that inhabit the individual, equivalent to our concept of the soul. Bodies preparation included coloured scented body ointments application, with a deep symbolic connotation and probably also a conservative purpose. The aim of this research was to characterize pigments and bind…

In-tube solid-phase microextraction and liquid chromatography using a monolithic column for the selective determination of residual ethylenediamine i…

2009

The selective determination of the diamine ethylenediamine (EDA) in the presence of a higher amount of residual dimethylamine in cationic polymers has been developed. The strategy uses both a solution derivatization with a selective agent of primary amines such as o-phthaldialdehyde-N-acetyl-L-cysteine (OPA-NAC) and an in-tube solid-phase microextraction (IT-SPME) coupled to liquid chromatography (LC). A 70 cm long, 0.32 mm internal diameter, and 3 microm thick commercially available capillary column coated with 95% polydimethylsiloxane and 5% polydiphenylsiloxane was employed to replace the injection loop of a Rheodyne injection valve. A volume of 1 mL of derivatized sample was passed thro…

Detector supports: application to aliphatic amines in wastewater

2005

Abstract Solid support assisted derivatization coupled to diffuse reflectance spectroscopy (DRS) was proposed and proved useful for the detection and quantification of aliphatic amines in water as an example. Dabsyl chloride (DBS), ninhydrin and sodium 1,2-naphtoquinone 4-sulphonate (NQS) were assayed as derivatization reagents. C 18 and SDB-XC disks and C 18 cartridges were tested for amine retention and after that derivatization. The decrease of the orange colour of dabsyl chloride on SBD-XC disks produced by the formation of its derivative with methylamine in the support (10 min at 100 °C) allowed the selective determination of the amine at concentration level equal or higher than 0.5 mg…

A new flow cell design for chemiluminiscence analysis.

2001

The present study proposes a new flow cell called a bundle cell for chemiluminescence analysis. The results obtained were compared with those achieved by manual and automated batch procedures and flow manifolds with different cells: an common quartz flow cell, a helix cell and the most used spiral cell. Figures of merit such as limit of detection, sensitivity, accuracy and precision for the Cr(III) determination were established with light emission produced by catalysed Cr(III) luminol oxidation by hydrogen peroxide in a basic aqueous solution. An improvement in sensitivity about 50% as compared with the spiral cell and even larger with respect to the other flow cells tested was observed. T…

Systematic Study of Several Causes and Effects Due to Absorbent Blanks in Determinations of One Analyte

1999

A systematic study is performed about several factors involved in the measurements when a absorbent blank is used, as molar absorption coefficient of the formed complex, absorbance of the blank at the measured wavelength, and kind of spectrophotometer used (conventional double-beam or diode-array). It is proved that the usual methodology, measuring against reagent blank, produces less accurate measurements than those obtained against solvent blank. On the other hand, use of the H-Point standard additions method provides always equal or better results than the best ones obtained at single wavelengths by using measurements against solvent bank, at the maximum of the formed complex. To test th…

Designing solid optical sensors for in situ passive discrimination of volatile amines based on a new one-step hydrophilic PDMS preparation

2016

Abstract We reported an optimal material for embedding chemoresponsive dyes based on modified commercial PDMS. A new approach to impart hydrophilicity to H-PDMS in an unique step was developed by addition of tetraethyl orthosilicate (TEOS) and in absence of basic or acid aqueous mixtures or hydroxyl-compounds during the PDMS coating process. This incorporation significantly enhances the performance of PDMS-based devices for sensing applications. New colorimetric sensors for passive detection and in situ discrimination of volatile amines have been obtained. The limit of detection achieved was 1.5 mg m −3 for both, dimethylamine and methylamine, suitable to control real working atmospheres. T…

CHROMATOGRAPHY: LIQUID | Multidimensional Chromatography

2000

A new tool for direct non-invasive evaluation of chlorophyll a content from diffuse reflectance measurements

2017

Abstract Chlorophyll is a key biochemical component that is responsible for photosynthesis and is an indicator of plant health. The effect of stressors can be determined by measuring the amount of chlorophyll a , which is the most abundant chlorophyll, in vegetation in general. Nowadays, invasive methods and vegetation indices are used for establishing chlorophyll amount or an approximation to this value, respectively. This paper demonstrates that H-point curve isolation method (HPCIM) is useful for isolating the signal of chlorophyll a from non-invasive diffuse reflectance measurements of leaves. Spinach plants have been chosen as an example. For applying the HPCIM only the registers of bo…

Estimation of the presence of unmetabolized dialkyl phthalates in untreated human urine by an on-line miniaturized reliable method

2015

Abstract At present, human exposure to dialkyl phthalates is assessed through urinary measurement of their metabolites due mainly to contamination in their analysis by their ubiquitous presence. An on-line miniaturized method and the processing of the untreated urine samples have been the key factors for minimizing contamination and achieving unbiased results. Di(2-ethylhexyl) (DEHP), diethyl (DEP), dibutyl (DBP) and mono-ethylhexyl (MEHP) phthalates in urine samples have been included in the study; MEHP as metabolite of the main dialkyl phthalate such as DEHP. On-line in-tube solid-phase microextraction (IT-SPME)-capillary liquid chromatography (CapLC) with diode array detection (DAD) is e…

A miniaturized method for estimating di(2-ethylhexyl) phthalate in bivalves as bioindicators.

2012

This work has developed a miniaturized method based on matrix solid phase dispersion (MSPD), using C18 as dispersant and acetonitrile-water as eluting solvent, for the analysis of di(2-ethylhexyl) phthalate (DEHP) in biota samples by capillary liquid chromatography coupled to in-tube solid phase microextraction and diode array detection. Recovery studies showed that the combination of C18-Florisil® was optimal using low amount of samples (0.1 g) and with low volumes of acetonitrile-water (2.6 mL 1:3.25, v/v). The sample is processed in less than 30 min, no evaporation step is required. The proposed method was applied to the analysis of DEHP in mussels and of the coastal waters in which they…

In-tube solid phase microextraction coupled to miniaturized liquid chromatography for both, noble metal nanoparticle assessment and sensitive plasmon…

2021

Abstract Colorimetric localized surface plasmon resonance (LSPR) as analytical response is applied for a wide number of chemical sensors and biosensors. However, the dependence of different factors, such as size distribution of nanoparticles (NPs), shape, dielectric environment, inter-particle distance and matrix, among others, can provide non-reliable results by UV–vis spectrometry in complex matrices if NP assessment is not carried out, particularly at low levels of analyte concentrations. Miniaturized liquid chromatography, capillary (CapLC) and nano (NanoLC), coupled on line with in-tube solid phase microextraction (IT-SPME) is proposed for the first time for both, controlling suitabili…

Ion-pair in-tube solid-phase microextraction and capillary liquid chromatography using a titania-based column: application to the specific lauralkoni…

2012

Abstract A quick, miniaturized and on-line method has been developed for the determination in water of the predominant homologue of benzalkonium chloride, dodecyl dimethyl benzyl ammonium chloride or lauralkonium chloride (C 12 -BAK). The method is based on the formation of an ion-pair in both in-tube solid-phase microextraction (IT-SPME) and capillary liquid chromatography. The IT-SPME optimization required the study of the length and nature of the stationary phase of capillary and the processed sample volume. Because to the surfactant character of the analyte both, the extracting and replacing solvents, have played a decisive role in the IT-SPME optimized procedure. Conditioning the capil…

Application of solid-phase microextraction combined with derivatization to the determination of amphetamines by liquid chromatography

2004

This work evaluates the utility of solid-phase microextraction (SPME) in the analysis of amphetamines by liquid chromatography (LC) after chemical derivatization of the analytes. Two approaches have been tested and compared, SPME followed by on-fiber derivatization of the extracted amphetamines, and solution derivatization followed by SPME of the derivatives formed. Both methods have been applied to measure amphetamine (AP), methamphetamine (MA), and 3,4-methylenedioxymethamphetamine (MDMA), using the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) and carbowax-templated resin (CW-TR)-coated fibers. Data on the application of the proposed methods for the analysis of different kin…

Analyser of chromium and/or cobalt

2003

Abstract Two stopped-flow manifolds have been proposed for individual or simultaneous determination of chromium and cobalt in water samples. Automated procedures based on multicommutation systems have emphasised the differences of their catalytic effect in luminol–hydrogen peroxide chemiluminescence reaction. A more rapid decay of signal was observed for Co for both configurations (flow injection or continuous injection). The influence of chemical and hydrodynamic variables has been studied in order to establish the robustness of method. The analysis rate was lower 1.5 min per replicate. Chemometric tools have been employed for the resolution of their contributions. Partial least squares (P…

On-line analysis of carbonyl compounds with derivatization in aqueous extracts of atmospheric particulate PM10 by in-tube solid-phase microextraction…

2011

Abstract A new device for carbonyl compounds based on coupling on-line and miniaturizing both, sample pretreatment and chromatographic separation, is reported. Two capillary columns, a GC capillary column (95% methyl–5% phenyl substituted backbone, 70 cm × 0.32 mm i.d., 3 μm film thickness) in the injection valve for in-tube solid-phase microextraction (IT-SPME) and a Zorbax SB C18 (150 mm × 0.5 mm i.d., 5 μm particle diameter) LC capillary column were employed. Different combinations of IT-SPME and derivatization using 2,4-dinitrophenylhydrazine (DNPH) were examined for mixtures containing 15 carbonyl compounds (aliphatic, aromatic and unsaturated aldehydes and ketones). A screening analys…

In-tube solid-phase microextraction coupled by in valve mode to capillary LC-DAD: Improving detectability to multiresidue organic pollutants analysis…

2009

Abstract A simple and fast capillary chromatographic method has been developed to identify and quantify organic pollutants at sub-ppb levels in real water samples. The major groups of pesticides (organic halogens, organic phosphorous, and organic nitrogen compounds), some hydrocarbons (polycyclic aromatic hydrocarbons), phthalates and some phenols such as phenol and bisphenol A (endocrine disruptors) were included in this study. The procedure was based on coupling, in-tube solid-phase microextraction (IT-SPME) by using a conventional GC capillary column (95% methyl–5% phenyl substituted backbone, 80 cm × 0.32 mm i.d., 3 μm film thickness) in the injection valve to capillary liquid chromatog…

Polydimethylsiloxane composites containing 1,2-naphtoquinone 4-sulphonate as unique dispositive for estimation of casein in effluents from dairy indu…

2015

A unique dispositive to determine casein which is the most abundant protein in dairy sewages has been proposed. In this sensing technology, the derivatization reagent 1,2-naphtoquininone 4-sulphonate (NQS) is embedded into a polydimethylsiloxane-tetraethylortosilicate-SiO2 nanoparticles composite (PDMS-TEOS-SiO2NPs). When the composite is immersed into the samples, casein is extracted from the solution and derivatized inside the PDMS matrix after 10 min at 100°C. The sensing support changes its color from yellow to orange depending on the casein concentration. Quantitative analysis can be carried out by measuring the absorbance with a reflection probe or by image-processing tool (GIMP). Thi…

Study of the influence of temperature and precipitations on the levels of BTEX in natural waters.

2013

Assessment of seasonal changes in surface water quality is an important aspect for evaluating temporal variation of water due to natural or anthropogenic inputs of point and non-point sources. The objective of this paper was to investigate the influence of seasonal temperature fluctuations and precipitations on the levels of BTEX in natural waters. Principal component analysis (PCA) was used to evaluate the seasonal correlations of BTEX levels in water and to extract the parameters that are most important in assessing seasonal variations of water quality. This study was carried out as a part of VOCs monitoring program in natural water samples from Mediterranean coast. To carry out this proj…

COMPARATIVE STUDY OF C18- AND STYRENE-DIVINYLBENZENE-BASED SORBENTS FOR THE ENRICHMENT OF PHENOLS FROM WATER

2001

The potential of solid-phase extraction with C18- and styrene divinylbenzene-based sorbents for the preconcentration of phenols from water samples has been evaluated for a variety of phenols of different polarities: phenol, o-, m- and p-cresol, 2-chlorophenol, and 4-chloro-3-methylphenol. The extraction efficiencies have been calculated for different volumes of samples containing the analytes at different concentration levels. The UV limits of detection were of 1–5 ng/mL, for the method using Bond Elut C18 cartridges and sample volumes of 25 mL, and 0.05–0.1 ng/mL (except for 4-chloro-3-methylphenol) for the method using the polymeric sorbent Bond Elut PPL and 1000 mL of the samples. Possib…

Sensitive and selective plasmonic assay for spermine as biomarker in human urine.

2014

A simple, fast, and highly selective and sensitive colorimetric assay to detect nanomolar levels of spermine in human urine (healthy donors, cancer patients) is reported. This assay is based on the absence of a competitive organic capping on the gold nanoparticles together with the high affinity of the amine groups of the analyte for the nanoparticle surface.

Multiresidue analysis of organic pollutants by in-tube solid phase microextraction coupled to ultra-high performance liquid chromatography-electrospr…

2013

In this work, in-tube solid phase microextraction (IT-SPME) coupling with ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) multiresidue analytical method has been proposed for the first time for on-line enrichment of 9 analytes included in Water Frame Directive 2000/60/EC (WFD). The device was equipped with a GC TRB-5 capillary column, used as pre-concentration loop, and two conventional six-port injection valves. Water sample and desorption solvent volumes were tested. The optimum conditions were 4mL of processed sample followed by elution with 40μL of methanol. The analytes were detected with a mass spectrometer after being ionized positively using an elect…

Combining poly(dimethyldiphenylsiloxane) and nitrile phases for improving the separation and quantitation of benzalkonium chloride homologues: In-tub…

2013

The retention and separation of four homologues of benzalkonium chloride (alkyl (C12, C14, C16, C18) dimethylbenzylammonium chloride) have been studied in poly(dimethyldiphenylsiloxane) (TRB) and nitrile capillary phases, respectively. Under the optimized conditions (50% acetonitrile in processed samples, 35% of diphenyl content of the TRB, capillary length 43 cm and water:methanol 60:40 as replacing solvent), the extraction efficiency was similar for all the homologues with satisfactory reproducibility and independently of the amount and proportion of homologues. Industrial samples with high viscosity or with complex composition and washes waters have been analyzed without previous treatme…

Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.

2005

Abstract The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o -phthaldialdehyde (OPA)– N -acetyl- l -cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA–NAC derivatives formed. The proposed conditio…

Scopolamine analysis in beverages: Bicolorimetric device vs portable nano liquid chromatography

2021

Abstract Scopolamine (SCP) is often involved in sexual assaults and robberies, particularly in recreational environments. Therefore, analytical tools are required for the analysis of this compound amenable for the field. In this work, a sensor for SCP is described based on the entrapment of KMnO4 into polydimethylsiloxane (PDMS). The possibility of using KMnO4 in combination with the reagent 1,2-naphtoquinone-4-sulfonate (NQS) giving a double sensor acting as a bicolorimetric device is also demonstrated. In contact with the sample, the PDMS composite delivers MnO4−, which reacts rapidly with SCP under basic conditions causing a change of the color of the solution that can be related to the …

Determination of amphetamines in hair by integrating sample disruption, clean-up and solid phase derivatization

2016

The utility of matrix solid phase dispersion (MSPD) for the direct analysis of amphetamines in hair samples has been evaluated, using liquid chromatography (LC) with fluorescence detection and precolumn derivatization. The proposed approach is based on the employment of MSPD for matrix disruption and clean-up, followed by the derivatization of the analytes onto the dispersant-sample blend. The fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) has been used for derivatization. Different conditions for MSPD, analyte purification and solid phase derivatization have been tested, using amphetamine (AMP), methamphetamine (MET), ephedrine (EPE) and 3,4-methylenedioxymethamphetamine (MDMA)…

H-Point standard additions method for resolution of binary mixtures with simultaneous addition of both analytes

1995

Abstract The basis of the H-point standard additions method, HPSAM, with simultaneous addition of both analytes is proposed for the resolution of binary mixtures. It is a modification of the previously described H-point standard additions method that permits the resolution of both species from a unique calibration set by making the simultaneous addition of the two analytes. The method uses as analytical signals the absorbances at pairs of wavelengths where each species shows the same absorbance. The required data to apply the method are the absorbance values at the previously selected wavelengths for the sample alone and spiked with both species at known concentrations. Linear relations bet…

Disinfection by-products effect on swimmers oxidative stress and respiratory damage.

2015

Disinfection by-products (DBPs) are generated through the reaction of chlorine with organic and inorganic matter in indoor swimming pools. Different DBPs are present in indoor swimming pools. This study evaluated the effects of different chlorinated formations in oxidative stress and lung damage in 20 swimmers after 40 min of aerobic swimming in 3 indoor pools with different characteristics. Biological samples were collected to measure lung damage (serum-surfactant-associated proteins A and B), oxidative stress parameters (plasma protein carbonylation and malondialdehyde, and whole-blood glutathione oxidation), and swimming exertion values (blood lactate) before and after exercise. Free chl…

Automated pre-column derivatization of amines in biological samples with dansyl chloride and with or without post-column chemiluminescence formation …

1999

On-line automation of two different liquid chromatographic procedures, a pre-column derivatization system and a pre- and post-column system, in order to generate chemiluminescence is reported. Dansyl chloride (Dns-Cl) was used as a pre-column reagent to form fluorophores and bis(2,4,6-trichlorophenyl) oxalate (TCPO) and hydrogen peroxide (H2O2) as a post-column reagent to generate chemiluminescence. This procedure is based on the employment of a primary column packed with C18 material inserted in a multi-dimensional assembly for sample clean-up and derivatization with Dns-Cl. The dansyl derivatives formed are transferred and separated in a LiChrospher 100 RP18 analytical column (125 x 4 mm …

Column-switching techniques for screening of diuretics and probenecid in urine samples

1994

A method based on high-performance liquid chromatography using column-switching is described for the screening of diuretics and probenecid in urine samples. The system uses a 20- x 2.1-mm i.d. precolumn, packed with a Hypersil ODS-C18, 30-microns stationary phase, for the on-line sample cleanup and enrichment. Untreated urine samples are directly injected, and the precolumn is flushed for 1 min with water to eliminate polar matrix components. The retained analytes are then back-flushed by means of a six-port switching valve onto a Hypersil ODS-C18 analytical column (5 microns, 250- x 4-mm i.d.), where they are separated using an acetonitrile/phosphate buffer (pH = 3) gradient elution. Under…

H-point standard additions method for resolution of overlapped chromatographic peaks with a conventional fluorescence detector. Determination of phen…

1996

The H-Point Standard Additions Method (HPSAM) is proposed in order to resolve overlapping peaks in liquid chromatography by using a conventional fluorescence detector. The method uses as analytical signals the heights or the areas obtained at two previously selected emission wavelengths, and good results are obtained for highly overlapping peaks with highly overlapping fluorescence spectra. The principal benefits of the method are the ease of finding the required wavelengths, its insensitivity to changes in the retention time of the peak from one injection to another, and the possibility of using it in highly or only partially overlapping peaks. We have applied the method to the determinati…

The generalized H-point standard-additions method to determine analytes present in two different chemical forms in unknown matrix samples. Part I. Ge…

2000

This paper shows how the generalized H-point standard-additions method (GHPSAM) can be used to obtain the total concentration or concentrations of different chemical forms of an analyte when the matrix of the sample is completely unknown. The spectral regions where the interferent behaviour can be considered as linear are found and the analyte concentration free from bias error is estimated. This paper includes the already published features of the GHPSAM and a new modification of this method which allows the simultaneous determination of two chemical forms of an analyte in a sample.

Comparative study of the determination of trimethylamine in water and air by combining liquid chromatography and solid-phase microextraction with on-…

2005

This work describes a new approach for the determination of trimethylamine (TMA) in water and air by liquid chromatography (LC). The assay is based on the employment of a solid-phase microextraction (SPME) fiber for sampling and for derivatization of the analyte with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC). The fiber, with a Carbowax-templated resin -50mum coating, was first immersed into a solution of the reagent. Once loaded with the reagent, the fiber was immersed into the water samples or exposed to the air samples in order to extract and to derivatize the analyte. Finally, the fiber was placed into a HPLC-SPME interface to desorb and transfer the TMA-FMOC derivat…

Analysis of 18 perfluorinated compounds in river waters: Comparison of high performance liquid chromatography–tandem mass spectrometry, ultra-high-pe…

2012

In this work, the performance of ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and capillary liquid chromatography-mass spectrometry (CLC-MS) has been studied for the analysis of eighteen perfluorinated compounds in water samples. UHPLC-MS/MS and CLC-MS analysis were carried out using a Zorbax C-18 column (50 mm × 2.1 mm, 1.8 μm) and a Zorbax SB-C18 column (150 mm × 0.5 mm, 3.5 μm), respectively, in gradient elution mode with a mobile phase of ammonium formate and methanol. Both techniques were compared with conventional LC-MS/MS in terms of speed, sensitivity, selectivity and resolution. Water samples were extracted by solid phase extraction (SPE). Mea…

On-line in-tube solid phase microextraction-capillary liquid chromatography method for monitoring degradation products of di-(2-ethylhexyl) phthalate…

2014

Abstract The main di-(2-ethylhexyl) phthalate (DEHP) degradation products, (2-ethylhexyl) phthalate (MEHP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), have been tested. The proposed cost-effective method combines on-line, in-tube solid-phase micro extraction (IT-SPME) in in-valve configuration and capillary liquid chromatography with UV diode array detection (Cap-LC-DAD). Acidification of the samples at pH 3 improved markedly the estimation of MEHP. Aliquots of 4 mL of acidified water samples were directly processed. After sample loading, the analytes were desorbed with the mobile-phase and transferred to the monolithic capillary column. Satisfactory linearity and precision, absen…

Solid-Phase Extraction and Clean-Up Procedures in Pharmaceutical Analysis

2012

Solid-phase extraction (SPE) using small cartridges filled with sorbents of a small particle size has rapidly established itself as an important sample clean-up technique. It has prospered at the expense of liquid-liquid extraction (LLE), which is considered labor intensive and frequently plagued by problems, such as emulsion formation and use of large volumes of hazardous solvents. A remarkable characteristic of SPE is its easy adaptation to on-line mode by column-switching techniques; switching can be effected manually or by automated controllers. The same analyte/sorbent interactions that are exploited in liquid chromatography (LC) are of use in SPE, but particle sizes employed are great…

Recent advances of in-tube solid-phase microextraction

2015

Abstract In-tube solid-phase microextraction (SPME) is ideally suited to developing green extraction by combining miniaturization, automation and reduction of solvent consumption. SPME has been used for the analysis of environmental, biological, and food samples, and numerous works have shown the benefits of using SPME. However, for full development of in-tube SPME, effort is still needed to overcome limitations, such as low extraction efficiency, selectivity and mechanical stability. To achieve these objectives, research on in-tube SPME is mainly focused in two scenarios: (1) the coupling of in-tube SPME with new chromatographic modalities, such as miniaturized liquid chromatography; and, …

Multivariate versus univariate calibration for nonlinear chemiluminescence data

2001

Abstract Multivariate calibration is tested as an alternative to model chromium(III) concentration versus chemiluminescence registers obtained from luminol-hydrogen peroxide reaction. The multivariate calibration approaches included have been: conventional linear methods (principal component regression (PCR) and partial least squares (PLS)), nonlinear methods (nonlinear variants and variants of locally weighted regression) and linear methods combined with variable selection performed in the original or in the transformed data (stepwise multiple linear regression procedure). Both the direct and inverse univariate approaches have been also tested. The use of a double logarithmic transformatio…

Footprint of carbonyl compounds in hand scent by in-tube solid-phase microextraction coupled to nano-liquid chromatography/diode array detection

2019

Abstract In the present work, the footprint of carbonyl compounds in hand scent was achieved by a miniaturized method consisting of sampling with cotton gauze, extraction and derivatization using 2,4-dinitrophenylhydrazine (DNPH) and preconcentration, separation and detection by in-tube solid-phase microextraction (IT-SPME) coupled to nano-liquid chromatography/Uv–vis diode array detection. The coupling IT-SPME-nanoLC-DAD was solved by using a two-valve system: the first valve for loading the sample and the second one to perform IT-SPME. To this aim, a nanoparticle-based capillary column was employed. Firstly, the transfer time from the load loop to the NP-based capillary column in the IT-S…

Influence of the presence of surfactants and humic acid in waters on the indophenol-type reaction method for ammonium determination.

2005

Abstract This work has evaluated the influence of humic acid and/or surfactants in the quantification of ammonium in waters with the indophenol-type reaction method. Thymol has been employed with the colorimetric method for sample ammonium concentrations between 0.25 and 1 mg L −1 . In addition, SPE/diffuse reflectance method has been used for quantification of ammonium at low concentrations (between 0.025 and 0.25 mg L −1 ). Matrix effect owing to humic substances were observed with the colorimetric method when the concentration was equal or higher than 25 mg L −1 . Lower concentrations of humic compounds produced matrix effects with the more sensitive SPE/diffuse reflectance method. Gener…

Amphetamine and Methamphetamine Determinations in Biological Samples by High Performance Liquid Chromatography. A Review

1994

Abstract This critical review shows the different high performance liquid chromatography methods proposed for amphetamine and methamphetamine determinations. It is directed mainly towards sample clean up and derivatizations steps, because of their significance in such determinations.

Evaluation of Superparamagnetic Silica Nanoparticles for Extraction of Triazines in Magnetic in-Tube Solid Phase Microextraction Coupled to Capillary…

2014

The use of magnetic nanomaterials for analytical applications has increased in the recent years. In particular, magnetic nanomaterials have shown great potential as adsorbent phase in several extraction procedures due to the significant advantages over the conventional methods. In the present work, the influence of magnetic forces over the extraction efficiency of triazines using superparamagnetic silica nanoparticles (NPs) in magnetic in tube solid phase microextraction (Magnetic-IT-SPME) coupled to CapLC has been evaluated. Atrazine, terbutylazine and simazine has been selected as target analytes. The superparamagnetic silica nanomaterial (SiO2-Fe3O4) deposited onto the surface of a capil…

In-tube solid-phase microextraction-capillary liquid chromatography as a solution for the screening analysis of organophosphorus pesticides in untrea…

2006

This paper describes a method for the selective screening of organophosphorus pesticides in water. In-tube solid-phase microextraction (SPME) in an open capillary column coupled to capillary liquid chromatography (LC) with UV detection has been used to effect preconcentration, separation and detection of the analytes in the same assembly. For in-tube SPME two capillary columns of the same length and different internal diameters and coating thicknesses have been tested and compared, a 30 cm x 0.25 mm I.D., 0.25 micro m thickness coating column, and a 30 cm x 0.1 mm I.D., 0.1 micro m of coating thickness column. In both columns the coating was 95% dimethylpolysiloxane (PDMS)-5% diphenylpolysi…

New optical paper sensor for in situ measurement of hydrogen sulphide in waters and atmospheres

2016

A novel and low-cost colorimetric sensor for the determination of hydrogen sulphide in environmental samples has been developed. This sensor is based on the immobilization of the reagent N,N-Dimethyl-p-phenylenediamine and FeCl3 in paper support, in which the H2S is adsorbed in order to give rise to the formation of methylene blue as reaction product. The sensor has been applied to determine H2S in water and air samples. Two different sampling systems for H2S caption from the air have been assayed: active and passive sampling. The analytical properties of the different systems have been obtained and compared. The analytical signals, corresponding to the methylene blue, have been obtained me…

Monofunctional pyrenes at carbon nanotube electrodes for direct electron transfer H2O2 reduction with HRP and HRP-bacterial nanocellulose

2021

Abstract The non-covalent modification of carbon nanotube electrodes with pyrene derivatives is a versatile approach to enhance the electrical wiring of enzymes for biosensors and biofuel cells. We report here a comparative study of five pyrene derivatives adsorbed at multi-walled carbon nanotube electrodes to shed light on their ability to promote direct electron transfer with horseradish peroxidase (HRP) for H2O2 reduction. In all cases, pyrene-modified electrodes enhanced catalytic reduction compared to the unmodified electrodes. The pyrene N-hydroxysuccinimide (NHS) ester derivative provided access to the highest catalytic current of 1.4 mA cm−2 at 6 mmol L−1 H2O2, high onset potential …

Improved detection limit for ammonium/ammonia achieved by Berthelot's reaction by use of solid-phase extraction coupled to diffuse reflectance spectr…

2005

Abstract The proposed procedure is based on the extraction of the indothylmol blue into C 18 solid-phase extraction (SPE) membranes and direct quantification on the membrane surface by diffuse reflectance spectroscopy. The analytical performance of the proposed method has been evaluated for standard solutions of ammonium using reflectance values, R , as well as the Kubelka–Munk function, F ( R ). The results have been compared with those obtained by the conventional method, which uses UV–vis absorption spectroscopy with a sensor-based method. The described methodology provided satisfactory linearity and reproducibility within the ammonium concentration intervals 25–250 μg L −1 and 25–500 μg…

Solid-Phase Extraction Techniques for Assay of Diuretics in Human Urine Samples

1991

Abstract Solid-phase extraction techniques were evaluated for the treatment of urine samples in the analysis of diuretics before injection into an HP-Hypersyl ODS-C18 column. Six different reversed-phase extraction columns were tested, and the results obtained are compared with those obtained in a classical liquid-liquid extraction with ethyl acetate. The solid-phase extraction procedures are the best overall choice for all the diuretics tested, due to their versatility, the minor time-consuming, and the good recovery percentages obtained. C18 and C8 packings give the highest recoveries for a majority of the diuretics studied. However, CH or PH columns, due to their greater selectivity, can…

Liquid chromatographic determination of trimethylamine in water.

2004

A method for the selective determination of trimethylamine (TMA) in aqueous matrices by liquid chromatography is reported. The proposed procedure is based on the derivatization of the analyte with 9-fluorenylmethyl chloroformate (FMOC) in a precolumn (Hypersil C18, 30 microm, 20 mm x 2.1 mm i.d.) connected on-line to the analytical column (LiChrosphere 100 RP18, 5 microm, 125 mm x 4 mm i.d.). Gradient elution was performed with a mixture of acetonitrile-water-0.05 M borate buffer (pH 9.0). The method has been applied to the direct determination of TMA in water within the 0.25-10.0 microg/ml concentration interval, and can also be adapted to the determination of TMA over the range 0.05-1.0 m…

A guide for selecting the most appropriate method for ammonium determination in water analysis

2006

Abstract We have critically evaluated the main parameters involved in determining ammonium in water samples, in order to select the most suitable method appropriate to the requirements of the analysis. We compared several methods: reference (ion-selective electrodes, Nessler and indophenol); Roth’s modified; based on luminol reaction; and, based on peroxioxalate reaction.

Bimodal copper oxide nanoparticles doped phase for the extraction of highly polar compounds by in-tube solid-phase microextraction coupled on-line to…

2020

Abstract Polymers obtained from tetraethyl orthosilicate (TEOS) and triethoxymethylsilane (MTEOS) have been functionalized with different metal and metal oxide nanoparticles (NPs), and used as coatings of extractive capillaries for the extraction of polar compounds by in-tube solid-phase microextraction (IT-SPME) coupled on-line to nano-liquid chromatography (nano-LC). The extraction capabilities of the new phases have been studied using several triazinic herbicides with log of octanol/water partition coefficients (Kow) ranging from -0.7 to 3.21 under reversed phase chromatographic conditions. Best extraction efficiencies for the most polar compounds (log Kow ≤ 2.3) were typically obtained …

Chiral determination of amphetamine and related compounds using chloroformates for derivatization and high-performance liquid chromatography

1999

The enantiomeric determination of amphetamine and various amphetamine-type compounds by liquid chromatography after chiral derivatization with 9-fluorenylmethyl chloroformate-L-proline (FMOC-L-Pro) is reported. The results obtained were compared with those achieved after achiral derivatization with 9-fluorenylmethyl chloroformate and subsequent separation of the derivatives on a beta-cyclodextrin chiral stationary phase. Conditions for the derivatization of amphetamines with FMOC-L-Pro were investigated, including the effect of the derivatization reagent concentration, pH and reaction time, using amphetamine, ephedrine and pseudoephedrine as model compounds. On the basis of these studies, p…

Determination of carbonyl compounds in particulate matter PM2.5 by in-tube solid-phase microextraction coupled to capillary liquid chromatography/mas…

2013

Abstract In this paper, a new procedure based on in-tube solid phase microextraction (IT-SPME)-capillary liquid chromatography hyphenated to mass spectrometry detection by using microelectrospray ionisation (CapLC–MS), has been reported. The device was proposed to quantify 12 carbonyl compounds (10 aliphatic aldehydes, an unsaturated aldehyde and a ketone) derivatized with 2,4-dinitrophenylhidrazine (DNPH) reagent in aqueous extracts of PM 2.5 . This methodology involves the on-line preconcentration of DNPH-carbonyl compounds derivatives coupled to the CapLC–MS system, efficiently providing appropriate sensitivity for the determination of the target analytes. Detection limits for the analyt…

Analysis of methylamine by solid-phase microextraction and HPLC after on-fibre derivatization with 9-fluorenylmethyl chloroformate

2004

Abstract A method for the determination of methylamine (MA) in aqueous matrices is reported which uses solid-phase microextraction (SPME) for enrichment and derivatization of the analyte, and high performance liquid chromatography (HPLC). The fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) has been used for derivatization. The SPME fibres were successively immersed in the samples and in the derivatization solutions to extract MA and FMOC, respectively. After a defined time of reaction, the derivatized analyte was desorbed into the chromatographic system, and chromatographed in a LiChrosphere 100 RP18, 125 mm ×4 mm i.d., 5 μm, column under gradient elution. In order to improve the…

Magnetic In-Tube Solid Phase Microextraction

2012

We report a new in-tube solid phase microextraction approach named magnetic in-tube solid phase microextraction, magnetic-IT-SPME. Magnetic-IT-SPME has been developed, taking advantage of magnetic microfluidic principles with the aim to improve extraction efficiency of IT-SPME systems. First, a magnetic hybrid material formed by Fe(3)O(4) nanoparticles supported on SiO(2) was synthesized and immobilized in the surface of a bared fused silica capillary column to obtain a magnetic adsorbent extraction phase. The capillary column was placed inside a magnetic coil that allowed the application of a variable magnetic field. Acetylsalicylic acid, acetaminophen, atenolol, diclofenac, and ibuprofen …

In Situ Analysis Devices for Estimating the Environmental Footprint in Beverages Industry

2019

Abstract The need to calculate the environmental footprint could mean the integration of sustainability in differentiation strategies for beverages industries. The parameters for estimating the footprint are outlined and discussed. The main negative impacts are related to water pollution, atmospheric pollution, and solid waste. Agro-industrial effluents may contain pesticides, complex oils, alkaline or acidic compounds, and other organic substances. As for atmospheric emissions, particulate material, SO2, NOx, hydrocarbons, and other organic compounds, can be mentioned. The state of art of in situ analysis devices for this purpose is described. The devices are compared through the tool CALI…

Curve resolution procedure for isolating the spectra of unknown interferences from the sample spectrum in analyte determinations

1998

The method described is based on the selection of a wavelength in the sample spectrum that is called ‘reference wavelength’, all measured wavelengths are previously assayed in order to select this reference wavelength. Several wavelengths can be used as the reference. The interferent spectrum is calculated as a function of the interferent absorbance at this wavelength, making use of the ratio between the absorbance of the analyte at the selected wavelength and at every measured wavelength. The proposed methodology can estimate the unknown interferent spectrum from the sample and pure analyte spectra. As a quality guarantee of the estimated spectrum, its shape is also estimated in spiked sam…

Miniaturized matrix solid phase dispersion procedure and solid phase microextraction for the analysis of organochlorinated pesticides and polybromina…

2009

Abstract This work has developed a miniaturized method based on matrix solid phase dispersion (MSPD) using C18 as dispersant and acetonitrile–water as eluting solvent for the analysis of legislated organochlorinated pesticides (OCPs) and polybrominated diphenylethers (PBDEs) in biota samples by GC with electron capture (GC-ECD). The method has compared Florisil®-acidic Silica and C18 as dispersant for samples as well as different solvents. Recovery studies showed that the combination of C18–Florisil® was better when using low amount of samples (0.1 g) and with low volumes of acetonitrile–water (2.6 mL). The use of SPME for extracting the analytes from the solvent mixture before the injectio…

Modifying the reactivity of copper (II) by its encapsulation into polydimethylsiloxane: A selective sensor for ephedrine-like compounds

2018

This paper demonstrates that the reactivity of copper (II) can be modified through its entrappment in a polymeric matrix of polydimethylsiloxane (PDMS), which makes possible the reaction into the support instead of in solution. Amino-containing compounds such as amino acids, proteins and sugars, which react with Cu (II) in solution, do not react inside the polymer. As a prove of concept, a highly specific Cu (II) PDMS-based sensor for ephedrines has been developed in this work. When the sensors are put into contact with solutions of these drugs under basic conditions, a change in their color from pale green to purple is observed. This change enables the visual identification of ephedrine (E…