Search results for "performance liquid chromatography"
showing 10 items of 649 documents
Determination of benzoylurea insecticides in food by pressurized liquid extraction and LC-MS
2010
A method based on pressurized liquid extraction and LC-MS/MS has been developed for determining nine benzoylureas (BUs) in fruit, vegetable, cereals, and animal products. Samples (5 g) were homogenized with diatomaceous earth and extracted in a 22 mL cell with 22 mL of ethyl acetate at 80 degrees C and 1500 psi. After solvent concentration and exchange to methanol, BUs were analyzed by LC-MS/MS using an IT mass analyzer, which achieved several transitions of precursor ions that increase selectivity providing identification. LOQs were between 0.002 and 0.01 mg/kg, which are equal or lower than maximum residue limits established by the Codex Alimentarius. Excellent linearity was achieved over…
Multi-class determination of antimicrobials in meat by pressurized liquid extraction and liquid chromatography–tandem mass spectrometry
2008
A multi-residue method using pressurized liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for determining trace levels of 31 antimicrobials, including beta-lactams, lincosamides, macrolides, quinolones, sulfonamides, tetracyclines, nitroimidazoles and trimethoprim. The extraction method required pre-homogeneization of the meat with EDTA-washed sand and subsequent one-static-cycle extraction for 10 min with 40 ml of water at 1500 psi and 70 degrees C. The effect of operation temperature, pressure, flush volume, and static cycles on PLE performance was studied. Average recoveries ranged from 75 to 99% with relative standard deviations <1…
Determinación de residuos de paraquat en lechuga y repollo cultivados en Lepaterique mediante HPLC-DAD
2018
La determinación de residuos del herbicida paraquat en lechuga (Lactuca sativa) y repollo (Brassica oleracea) producidos en la comunidad de La Brea, Lepaterique y comercializados en la ciudad de Tegucigalpa fue llevada a cabo en los meses de octubre y noviembre de 2017, mediante la aplicación de cromatografía líquida de elevada resolución con detector de arreglo de diodos (HPLC-DAD) en menos de 6 minutos, con un mecanismo de separación de fase reversa empleando una columna superficialmente porosa C18 y una mezcla de ácido orto fosfórico al 0.1 M (pH 3,0) con acetonitrilo en proporción de 3:1 como fase móvil. El método se basa en la extracción con baño ultrasónico utilizando agua como solven…
Selective solid-phase extraction of organophosphorus pesticides and their oxon-derivatives from water samples using molecularly imprinted polymer fol…
2020
Abstract A molecularly imprinted polymer was synthesized and characterized to be used as solid-phase extraction sorbent for simultaneous chlorpyrifos and diazinon and their oxon derivatives. Several imprinted polymers were prepared and evaluated in a retention study of these analytes compared with a non-printed polymer. Several parameters affecting the extraction of imprinted polymer such as washing solvent, composition and volume of the eluting solvent and sample volume, were also investigated. Under the optimum conditions, the developed method provided satisfactory limits of detection ranging between 0.07 µg L−1 to 0.12 µg L−1 and the material showed an excellent reusability (> 50 reuses)…
Evaluation of solid-phase extraction and stir-bar sorptive extraction for the determination of fungicide residues at low-microg kg(-1) levels in grap…
2004
Abstract A liquid chromatography–mass spectrometry method has been developed for determining bitertanol, carboxin, flutriafol, pyrimethanil, tebuconazole and triadimefon. The evaluation of both atmospheric pressure interfaces (API), atmospheric pressure chemical ionization (APCI) and electrospray (ESI) using positive and negative ionization modes, clearly shows that the studied pesticides are more sensitive using APCI in positive mode. Two procedures based on solid-phase extraction (SPE) and stir-bar sorptive extraction (SBSE) have been assessed for extracting these compounds in grape. The recoveries obtained by SPE in samples spiked at the limit of quantification (LOQ) level ranged from 60…
Analysis of currently used pesticides in fine airborne particulate matter (PM 2.5) by pressurized liquid extraction and liquid chromatography-tandem …
2008
During and after the application of currently used pesticides (CUPs) a significant fraction of applied pesticides can be lost to the air. A confirmatory and rapid procedure has been developed for the determination of four fungicides (carbendazim, thiabendazol, imazalil and bitertanol), three insecticides (imidacloprid, methidathion and pyriproxyfen), one helicide (methiocarb) and one acaricide (hexythiazox) in fine airborne particulate matter (PM 2.5) at trace level. The proposed method includes extraction of PM 2.5-bound pesticides by pressurized liquid extraction (PLE) followed by a direct injection into LC-MS/MS. The main parameters affecting the performance of the electrospray ionizatio…
Determination of sulphonamides in human urine by azo dye precolumn derivatization and micellar liquid chromatography
1995
Abstract A high-performance liquid chromatographic method for the determination of sulphonamides in urine is reported. The drugs (sulphadiazine, sulphaguanidine, sulphamethizole, sulphamethoxazole, and sulphathiazole) were diazotized with nitrite and coupled with N-(1-naphthyl)ethylenediamine dihydrochloride in a sodium dodecyl sulphate (SDS) micellar medium. Separation of the sulphonamide azo dyes was performed on a C18 column with a 0.05 M SDS-2.4% pentanol mobile phase, which permitted the direct injection of the urine samples. The limits of detection were in the 0.1–0.3 μg/ml range.
Identification of the Biotransformation Products of 2-Ethylhexyl 4-(N,N-Dimethylamino)benzoate
2010
Nowadays, 2-ethylhexyl 4-(N,N-dimethylamino)benzoate (EDP) is one of the most widely used UV filters in sunscreen cosmetics and other cosmetic products. However, undesirable processes such as percutaneous absorption and biological activity have been attributed to this compound. The in vitro metabolism of EDP was elucidated in the present work. First of all, the phase I biotransformation was studied in rat liver microsomes and two metabolites, N,N-dimethyl-p-aminobenzoic acid (DMP) and N-monomethyl-p-aminobenzoic acid (MMP), were identified by GC-MS analysis. Secondly, the phase II metabolism was investigated by means of LC-MS. The investigated reactions were acetylation and glucuronidation …
Simple and sensitive reversed-phase liquid chromatographic assay for analysis of chlorthalidone in urine
1993
Abstract This study describes a rapid method for the determination of chlorthalidone in human urine by reversed-phase liquid chromatography and UV detection at 230 nm, after clean-up over a C8 solid-phase extraction column. Liquid chromatography was carried out on a C18-bonded phase using acetonitrile-phosphate buffer (pH=3) gradient elution. Triamterene was used as internal standard. The system has been applied to the determination of chlorthalidone in the 0.10–10.0 μg/mL concentration interval; the limit of detection was 6 ng/mL.
Comparison of different sorbents for on-line liquid-solid extraction followed by high-performance liquid chromatographic determination of nitrogen-co…
1998
Abstract LiChrolut EN [poly(styrene-divinylbenzene), PSDVB], Carbograph (graphitized carbon black, GCB), Isolute CN (cyanopropylsilica), Isolute C 2 (ethylsilica), and LiChrospher RP18 (octadecylsilica) were studied for on-line solid-phase extraction of twelve nitrogen containing pesticides from water. Determination (UV 210 nm) was performed with a Spherisorb C 8 analytical column and an acetonitrile-water gradient. The mean recoveries from 50 ml ranged from 83% for RP18 to 44% for GCB, and decreased in the following order: RP18, CN, LiChrolut EN, C 2 , and GCB. GCB showed poor recoveries due to incomplete desorption with the acetonitrile-water gradient used, and memory effects were detecte…