Search results for "Detection limit"
showing 10 items of 810 documents
Fluorimetric determination of 1-naphthol and mixtures of carbaryl and 1-naphthol in micellar media
1990
The interaction of 1-naphthol with different types of anionic, cationic and non-ionic surfactants has been studied spectrofluorimetrically in order to obtain a sensitivity enhancement in the determination of this compound. At neutral pH, cetyl trimethyl ammonium bromide (CTAB) provides a 2-fold sensitivity enhancement of 1-naphthol and exhibits a weak interaction with carbaryl. In strong alkaline medium carbaryl is hydrolyzed to 1-naphthol and in the presence of CTAB micells, a 5-fold sensitivity enhancement and a limit of detection of 0.2 μg·ml−1 with a 101±3% percentage of recovery is obtained. These facts permit the development of an accurate method for the fluorimetric analysis of 1-nap…
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…
Determination of Phenol by Preconcentration‐Direct Chemiluminescence in a FIA Assembly
2005
Abstract The determination of phenol in water samples is proposed with the aid of a flow‐injection system. The analytical procedure is based on the direct chemiluminometric emission by oxidation of the analyte with potassium permanganate in acidic medium. The flow assembly is provided with a solid‐phase reactor filled with a resin type XAD‐4 for analyte preconcentration. A large study of potential interferences, namely, amino acids reaching water through degradation of organic matter; metals and inorganic metal ions typically present in water interfering with the CL emission of the parent compound, was performed. The calibration graph was linear over the phenol concentration range 1.0–20.0 …
Analysis of drugs including illicit and new psychoactive substances in oral fluids by gas chromatography-drift tube ion mobility spectrometry
2021
Abstract In this study, a gas chromatograph (GC) has been coupled to a drift tube ion mobility spectrometer (IMS) in order to develop an analytical procedure for the determination of psychoactive substances in oral fluids. Working parameters, including the GC-IMS interface ones, were adjusted in order to obtain sensitive and robust signals. A volume of 500 μL of oral fluid was extracted with 250 μL chloroform and, after centrifugation, were injected into the GC-IMS system. Amphetamine, methylone, α-PVP, ketamine, lidocaine, MPHP, cocaine, THJ-2201, and 5F-ADB were employed as model compounds, providing limits of detection from 6 to 15 μg L−1 and recoveries from 70 to 115% for field oral flu…
Determination of tea tree oil terpenes by headspace gas chromatography mass spectrometry
2016
An alternative procedure was developed for determining quality control of terpenes in tea tree oil commercial samples. The method is based on static headspace gas chromatography mass spectrometry measurements. Absolute limits of detection ranged from 1 ng for p-cymene to 71 ng for terpinen-4-ol. The accuracy of the developed methodology was evaluated by comparing the obtained eucalyptol and terpinen-4-ol concentrations with those provided for a certified sample and by comparing the developed procedure with literature tea tree oil analysis methodology. In the same way, spiked commercial samples provided recovery values ranging between 94% and 100% for all the target analytes with relative st…
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…
Ionic liquid-based single-drop microextraction followed by liquid chromatography-ultraviolet spectrophotometry detection to determine typical UV filt…
2009
Abstract A user-friendly and inexpensive ionic liquid-based single-drop microextraction (IL-SDME) procedure has been developed to preconcentrate trace amounts of six typical UV filters extensively used in cosmetic products (i.e., 2-hydroxy-4-methoxybenzophenone, isoamyl 4-methoxycinnamate, 3-(4′-methylbenzylidene)camphor, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate, 2-ethylhexyl 4-dimethylaminobenzoate and 2-ethylhexyl 4-methoxycinnamate) from surface water samples prior to analysis by liquid chromatography-ultraviolet spectrophotometry detection (LC-UV). A two-stage multivariate optimization approach was developed by means of a Plackett–Burman design for screening and selecting the significa…
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…
Green determination of eight water-soluble B vitamins in cosmetic products by liquid chromatography with ultraviolet detection.
2021
Abstract B vitamins are a group of compounds with beneficious properties for dermatologic care, and therefore they are included in the cosmetic formulations as high added-value ingredients. In this paper, an analytical method for the simultaneous determination of eight water-soluble B vitamins in cosmetic products is reported for the first time. This method is based on liquid chromatography with ultraviolet detection (LC-UV) analysis after simple water leaching of the analytes from the cosmetic matrix. No organic solvents are required, beyond the ethanol used in the chromatographic mobile phase. The proposed method has been successfully validated showing good linearity, limits of detection …
Sequential-injection determination of traces of disodium phenyl dibenzimidazole tetrasulphonate in urine from users of sunscreens by on-line solid-ph…
2005
Abstract A sensitive and selective method to determine disodium phenyl dibenzimidazole tetrasulphonate (PDT) in the urine of sunscreen users, which is suitable for studies on body accumulation/excretion is proposed. On-line solid-phase extraction allows the analyte to be retained and subsequentely eluted, using a strong anion exchange (SAX) microcolumn. Standard addition calibration was carried out with only one standard. The wavelengths of excitation and emission were 330 and 454 nm, respectively. The method allows PDT to be determined in both, spiked and unspiked human urine samples, without any pre-treatment. Results obtained for spiked urine samples (40–200 ng ml −1 ) showed the accurac…