Search results for " Phase"
showing 10 items of 1862 documents
Amphetamine and methamphetamine determination in urine by reversed-phase high-performance liquid chromatography with sodium 1,2-napthoquinone 4-sulfo…
1995
A rapid method is described for the identification and determination of amphetamine and methamphetamine in human urine samples by liquid chromatography with UV-Vis detection. The samples were transferred onto a C18 solid-phase extraction column and chromatographed on a Hypersil ODS RP C18, 5 microns (250 x 4 mm I.D.) with an acetonitrile-water elution gradient containing propylamine. Under these conditions, the amines are eluted with a short retention time. The procedure has been applied to the determination of amphetamine and methamphetamine in the range 0.3-4.0 micrograms/ml in spiked urine samples. The detection limits at 280 nm were 4 and 2 ng/ml for amphetamine and methamphetamine, res…
Automated Determination of Trimipramine and N-Desmethyl-Trimipramine in Human Plasma or Serum by HPLC With On-Line Solid Phase Extraction
1995
A fully automated method including column-switching and isocratic high performance liquid chromatography (HPLC) was developed for determination of the tricyclic antidepressant trimipramine (T) and its N-demethylated metabolite N-desmethyltrimipramine (DT). The limit of quantification was below 10 ng/ml for T and DT. The assay revealed linearity between detector response and drug concentration in a therapeutically relevant range of 10 to 500 ng/ml. The mean intra- and interassay variabilities were 6.2 and 12.3%, respectively, for T and 4.7 and 8.7% respectively, for DT. The method can be applied to therapeutic drug monitoring of patients under T therapy and may be useful for pharmacokinetic …
Determination of inorganic species by thermal lens spectrometry
1997
Abstract The application of thermal lens spectrometry (TLS) to the determination of inorganic species is reviewed. The requirements of a chromogenic reaction to be advantageously adapted to TLS detection, and the necessary conditions for reaching very low limits of detection are discussed. Methods for the determination of metals and P, Si, S and N compounds in several samples are examined. Flow-injection and extraction methods, associated photoinduced reactions and surface phenomena, speciation and equilibrium studies are discussed. Gas phase NO 2 methods are also commented upon. Trends are given.
Matrix effects on solid-phase microextraction of organophosphorus pesticides from water
1997
Abstract This study develops a method for solid-phase microextraction (SPME) of eight organophosphorus pesticides, diazinon, fenthion, fenitrothion (sumithion), methyl-parathion, parathion, methyl-trithion, ethion and triazophos, from water. Determination is carried out by gas chromatography with nitrogen-phosphorus detection. To perform the SPME, poly(dimethylsiloxane) and polyacrylate fibers were initially compared on the basis of their absorption capacities for the selected pesticides, and polyacrylate was selected to accomplish the rest of assays. The main factors affecting the SPME process such as memory effect, stirring rate, extraction temperature and absorption-time profile were stu…
Gas chromatographic behaviour of urea herbicides
2001
Gas chromatographic conditions for determining eight phenylurea (chlortoluron, diuron, fluometuron, isoproturon, linuron, metabenzthiazuron, metobromuron and monuron) and one sulfonylurea (chlorsulfuron) herbicides were assessed. Degradation products of the herbicides formed in the injector were used for identification. Most phenylureas formed their respective carbamic acid methyl esters, metabenzthiazuron formed an aminobenzothiazol and chlorsulfuron formed an aminotriazine plus a phenylsulfonamide. On-column injection of standards using a BP10 capillary column was evaluated to identify the chromatographic behaviour. Detection limits ranged from 0.05 ng for chlorsulfuron to 3 ng for monuro…
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…
Determination of organophosphorus pesticides in honeybees after solid-phase microextraction.
2001
A method based on solid-phase microextraction (SPME) followed by gas chromatography with nitrogen-phosphorus detection was developed for the purpose of determining 18 organophosphorus pesticide residues in honeybee samples (Apis mellifera). The extraction capacities of polyacrylate and poly(dimethylsiloxane) fibers were compared. The main factors affecting the SPME process, such as the absorption time profile, salt, and temperature, were optimized. The method involved honeybee sample homogenization, elution with an acetone:water solution (1:1) and dilution in water prior to fiber extraction. Moreover, the matrix effect on the extraction was evaluated. In samples spiked at the 0.2 mg kg(-1) …
Determination of N -nitrosamines in cosmetic products by vortex-assisted reversed-phase dispersive liquid-liquid microextraction and liquid chromatog…
2018
A new analytical method for the simultaneous determination of trace levels of seven prohibited N-nitrosamines (N-nitrosodimethylamine, N-nitrosoethylmethylamine, N-nitrosopyrrolidine, N-nitrosodiethylamine, N-nitrosopiperidine, N-nitrosomorpholine, and N-nitrosodiethanolamine) in cosmetic products has been developed. The method is based on vortex-assisted reversed-phase dispersive liquid-liquid microextraction, which allows the extraction of highly polar compounds, followed by liquid chromatography with mass spectrometry. The variables involved in the extraction process were studied to obtain the highest enrichment factor. Under the selected conditions, 75 μL of water as extraction solvent …
DETERMINATION OF PENTOBARBITAL IN BIOLOGICAL SAMPLES BY MICELLAR LIQUID CHROMATOGRAPHY
1999
A liquid chromatographic procedure for the determination of pentobarbital in urine and plasma samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C18 analytical column, a guard column of similar characteristics, and a 0.02 M CTAB-15% 1-propanol at pH 7.5 mobile phase. The UV detector was set at 250 nm. Pentobarbital was isolated from urine and plasma samples by using a single solid phase extraction procedure with LMS cartridges. Mephobarbital was used as internal standard. Limits of detection were 0.53 μg/mL and 0.60 μg/mL in urine and plasma samples respectively. In both cases the coefficients of variation were lower than 6.5%, and the recoveries ranged betwe…
Determination of abamectin in citrus fruits by liquid chromatography-electrospray ionization mass spectrometry.
2000
Liquid chromatography coupled to electrospray mass spectrometry (LC-ES-MS) with positive ion detection was used to determine abamectin in oranges. MS conditions were optimized to achieve maximum sensitivity. The main ion for abamectin was [M+Na]+ at a fragmentor voltage of 180 V. Abundant structural information can be obtained at different fragmentor voltages. The detection limit for the standard solution was 12 pg injected, and good linearity and reproducibility were observed. Abamectin residues were extracted using matrix solid-phase dispersion. Orange samples were homogenized with C18 bonded silica placed onto a glass column and eluted with dichloromethane. Recoveries of the abamectin fr…