Search results for "LIMIT"
showing 10 items of 2826 documents
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…
Chemiluminometric photo-induced determination of Strychnine in a Multicommutation flow assembly
2007
This paper deals on the determination of Strychnine, a potent and dangerous pesticide and the analytical procedure is based on the photo-induced chemiluminescence of the pesticide by means of the Multicommutation continuous-flow methodology. Small segments of the pesticide solution were sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. The required time of UV irradiation was obtained by stopped-flow during 150 s; then, the resulting solution formed alternated segments with the oxidizing solution containing 5 × 10−3 mol l−1 Ce(IV) in 0.6 mol l−1 nitric acid. The calibration range, from 2 μg l−1 to 50 mg l−1, resulted in a linear…
Determination of phenolic compounds in air by using cyclodextrin-silica hybrid microporous composite samplers
2015
An analytical method for the determination of phenolic compounds in air samples based on the use of cyclodextrin-silica hybrid microporous composite samplers is proposed. The method allows the determination of phenol, guaiacol, cresol isomers, eugenol, 4-ethylphenol and 4-ethylguaiacol in workplaces according to the Norm UNE-EN 1076:2009 for active sampling. Therefore, the proposed method offers an alternative for the assessment of the occupational exposure to phenol and cresol isomers. The detection limits of the proposed method are lower than those for the NIOSH Method 2546. Storage time of samples almost reaches 44 days. Recovery values for phenol, guaiacol, o-cresol, m-cresol, p-cresol,…
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…
Use of micellar mobile phases for the chromatographic determination of clorazepate, diazepam, and diltiazem in pharmaceuticals
2001
An ODS-2 column, a micellar mobile phase of high elution strength containing 0.1M sodium dodecyl sulfate and 3% (v/v) butanol, and ultraviolet detection at 230 nm are used for the determination of either of two benzodiazepines (clorazepate and diazepam) and a benzothiazepine (diltiazem) in pharmaceuticals. The procedure is shown to be competitive against conventional chromatography with methanol-water mobile phases, especially for diltiazem. The composition of the micellar mobile phase is selected using a predictive strategy based on an accurate retention model and assisted by computer simulation. Calibration graphs are linear at least in the 2.5 to 20 microg/mL, 4 to 20 microg/mL, and 5 to…
Evaluation of working air quality by using semipermeable membrane devices
2008
Abstract It has been evaluated the use of semipermeable membrane devices (SPMDs) as passive samplers of organophosphorus pesticides from air, in order to determine the contamination of working environments. Additionally, the use of SPMDs as portable samplers has been also considered. The analytical methodology for the determination of diazinon, chlorpyrifos-methyl, pirimiphos-methyl, chlorpyrifos and fenthion in SPMDs exposed to contaminated air was based on microwave-assisted extraction and gas chromatography with mass spectrometry determination. Limit of detection (LOD) values from 2 to 4 ng SPMD−1 and repeatability from 2 to 7% were obtained by using the aforementioned methodology. Theor…
A rapid and sensitive gas chromatography-mass spectrometry method for the quality control of perfumes: simultaneous determination of phthalates
2013
A rapid and sensitive analytical gas chromatography-mass spectrometry (GC-MS) method for perfume analysis to determine the phthalates banned by the European Union Regulation on cosmetic samples is presented. This method has been tested in commercial alcoholic perfume samples for the determination of the following seven phthalates: dibutyl phthalate, bis(2-ethylhexyl) phthalate, bis(2-methoxyethyl) phthalate, n-pentyl-isopentylphthalate, di-n-pentyl phthalate, diisopentylphthalate and benzyl butyl phthalate. Sample evaporation and redissolution in ethanol is carried out before GC-MS analysis, with no dilution of the sample. External calibration and standard addition calibration are compared …
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…
Determination of arsenic and antimony in milk by hydride generation atomic fluorescence spectrometry
2002
Abstract A highly sensitive procedure has been developed for total arsenic and antimony determination in milk samples by hydride generation atomic fluorescence spectrometry after microwave-assisted sample digestion. The discrete introduction of 2 ml of digested sample in the automated continuous flow hydride generation system allows us to reduce drastically the sample and HCl consume and to determine several elements from a same sample digestion. The method provides detection limits of 0.006 and 0.003 ng ml−1, a sensitivity of 2390 and 2840 fluorescence units per ng ml−1 for As and Sb respectively, and average relative standard deviation of 2.3% for As and 4.8% for Sb. The analysis of cow m…
On-line solvent recycling: a tool for the development of clean analytical chemistry in flow injection Fourier transform infrared spectrometry. Determ…
1998
Abstract A flow injection strategy has been developed for the direct determination of ketoprofen in pharmaceuticals by Fourier transform infrared spectrometry also incorporating a distillation unit which allows the carbon tetrachloride employed to dissolve samples and standards and used as a carrier to be recovered on-line. The system developed permits a drastic reduction of reagent consumption and easy and fast sampling and cleaning of the measurement cell. For the quantification of ketoprofen in pharmaceuticals the carbonyl bands at 1712 and 1666 cm −1 were employed and the developed method provided a 3 σ limit of detection of 0.04 mg ml −1 , a dynamic range up to 10 mg ml −1 and typical …