Search results for "Detection limit"
showing 10 items of 810 documents
Chromatographic determination of diuretics in urine samples using hybrid micellar mobile phases with fluorimetric detection
1998
Abstract A rapid and simple chromatographic procedure, that uses hybrid micellar mobile phases of sodium dodecyl sulphate (SDS), propanol and phosphate buffer at pH 3, and fluorimetric detection ( λ exc =270 nm, λ em =430 nm), is reported for the determination of mixtures of seven diuretics of diverse efficacy (amiloride, bendroflumethiazide, bumetanide, furosemide, hydroflumethiazide, piretanide and triamterene), in urine samples. The application of a sequential optimization procedure for the resolution of the mixtures of the diuretics was problematic. However, their separation was achieved through the use of an interpretive optimization procedure based on the accurate description of the r…
Rapid determination of sterols in vegetable oils by CEC using methacrylate ester-based monolithic columns
2008
A method for the determination of sterols in vegetable oils by CEC with UV-Vis detection, using methacrylate ester-based monolithic columns, has been developed. To prepare the columns, polymerization mixtures containing monomers of different hydrophobicities were tried. The influence of composition of polymerization mixture was optimized in terms of porogenic solvent, monomers/porogens and monomer/crosslinker ratios. The composition of the mobile phase was also studied. The optimum monolith was obtained with lauryl methacrylate monomer at 60:40% (wt:wt) lauryl methacrylate/ethylene dimethacrylate ratio and 60 wt% porogens with 20 wt% of 1,4-butanediol (12 wt% 1,4-butanediol in the polymeriz…
Multivariate optimization of the hollow fibre liquid phase microextraction of muscimol in human urine samples.
2016
Abstract A liquid phase microextraction based on hollow fibre followed by liquid chromatographic determination was developed for the extraction and quantitation of the hallucinogenic muscimol from urine samples. Method applicability on polar hallucinogens was also tested on two alkaloids, a psychedelic hallucinogen, tryptamine and a polar amino acid, tryptophan which exists in its charged state in the entire pH range. A multivariate design of experiments was used in which a half fractional factorial approach was applied to screen six factors (donor phase pH, acceptor phase HCl concentration, carrier composition, stirring rate, extraction time and salt content) for their extent of vitality i…
Liquid chromatographic determination of Vitamin D3 in infant formulas and fortified milk
2005
Abstract An isocratic reverse-phase liquid chromatographic (LC) method with electrochemical (EC) detection has been developed and validated for determining Vitamin D 3 in fortified milk and infant formulas. LC–EC determination provides linear responses in the range from 0.03 to 0.7 μg Vitamin D 3 /ml, with inter- and intra-day variations (R.S.D.%) of 4.1 and 4.4, respectively, and detection and quantification limits of 0.012 ng in assay (48 ng/100 g of sample) and 0.039 ng in assay (156 ng/100 g of sample), respectively. Application of the method to a set of infant formulas and fortified milk confirmed its usefulness.
An on-line system for preconcentration and determination of lead in wine samples by FAAS
2002
A flow injection method has been developed for the direct determination of free available Pb(II) and total Pb content in wine samples. The method is based on the chemical sorption of Pb(II), from pH 7 buffered solutions, on a packed polyurethane foam column, modified by addition of 2-(2-benzothiazolylazo)-p-cresol (BTAC). After this step, lead was directly eluted with a stream of 0.1 mol l(-1) HCl into an air C(2)H(2) flame in which lead was determined by atomic absorption spectrometry. Total lead was analyzed after sample digestion with nitric acid and hydrogen peroxide, being free available lead determined by direct sample on-line preconcentration and elution. The method provides a limit …
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 …
Date-rape evidence through fast determination of γ-butyrolactone in adulterated beverages.
2021
Abstract An infrared spectroscopy (IR) based methodology has been developed to determine γ-butyrolactone (GBL) in adulterated beverages. The proposed method permits the direct screening of GBL in beverages and involves a minimum sample treatment requiring less than 2 min for quantitative determination of GBL. Sensitivity of IR method was improved by using liquid-liquid extraction (LLE) providing detection limits of 0.023 mg g−1. Accuracy of the proposed methodology was evaluated through the analysis of soft beverages and alcoholic cocktails spiked with GBL at concentration levels ranging from 0.075 to 10 mg g−1 providing recovery values from 91 to 100%. GBL was determined in twelve blind-sp…
Determination at low ppm levels of dithiocarbamate residues in foodstuff by vapour phase-liquid phase microextraction-infrared spectroscopy
2010
Abstract A methodology based on the vapour phase (VP) generation of carbon disulphide from non-volatile dithiocarbamate compounds has been developed for determination of pesticide residues in foodstuff at low ppm levels. The method involves a selective reaction combined with liquid phase microextraction (LPME) and transmission infrared measurements. The use of a home made transmission cell improved the detection limits (LOD) compared to the use of attenuated total reflectance measurements by a factor of approximately 80. Using the most appropriate experimental conditions for the CS2 generation and LPME preconcentration, the precision of the methodology, expressed as the relative standard de…
Gas sensors arrays (electronic noses) : a study about the speed/accuracy ratio
2000
Abstract New Fingerprint Mass Spectra (FMS) systems claim for a higher precision, a reduced analysis time, and a lower drift, compared with Gas Sensors Arrays ‘Electronic Noses’. We demonstrated in this study that metal oxide gas sensors may have highly improved performances for both accuracy and run time, when used in optimum conditions. The different noise components were quantified referring to popular words (equivalent of ethanol concentration) using the transfer function of the sensor. It was pointed out that sample surrounding greatly affects the noise level, and that the signal-to-noise ratio may be dramatically increased, reducing the distortion generally assessed between sensor and…
Acetone Vapor-Sensing Properties of Chitosan-Polyethylene Glycol Using Surface Plasmon Resonance Technique
2020
To non-invasively monitor and screen for diabetes in patients, there is need to detect low concentration of acetone vapor in the range from 1.8 ppm to 5 ppm, which is the concentration range of acetone vapor in diabetic patients. This work presents an investigation for the utilization of chitosan-polyethylene glycol (PEG)-based surface plasmon resonance (SPR) sensor in the detection of trace concentration acetone vapor in the range of breath acetone in diabetic subjects. The structure, morphology, and elemental composition of the chitosan-PEG sensing layer were characterized using FTIR, UV-VIS, FESEM, EDX, AFM, and XPS methods. Response testing was conducted using low concentration of aceto…