Study of the degradation products of bromopropylate, chlordimeform, coumaphos, cymiazole, flumethrin and tau-fluvalinate in aqueous media.

Degradation processes of bromopropylate, coumaphos, chlordimeform, cymiazole, flumethrin and fluvalinate in aqueous media have been studied by HPLC. Cymiazole is stable at any tested pH (1-11), while bromopropylate, flumethrin and coumaphos are unstable at basic pH and chlordimeform and fluvalinate in neutral and basic media. The main degradation products have been identified by GC-MS. The reaction rate constants and half-lives were calculated and the effect of co-solvents on the rate and product profile was studied.

Study of the solid-phase extraction of diclofenac sodium, indomethacin and phenylbutazone for their analysis in human urine by liquid chromatography.

A selective semi-automated solid-phase extraction (SPE) of the non-steroidal anti-inflammatory drugs diclofenac sodium, indomethacin and phenylbutazone from urine prior to high-performance liquid chromatography was investigated. The drugs were recovered from urine buffered at pH 5.0 using C18 Bond-Elut cartridges as solid sorbent material and mixtures of methanol-aqueous buffer or acetonitrile-aqueous buffer as washing and elution solvents. The extracts were chromatographed on a reversed-phase ODS column using 10 mM acetate buffer (pH 4.0)-acetonitrile (58:42, v/v) as the mobile phase, and the effluent from the column was monitored at 210 nm with ultraviolet detection. Absolute recoveries of the anti-inflammatory drugs within the range 0.02-1.0 microg/ml were about 85% for diclofenac and indomethacin, and 50% for phenylbutazone without any interference from endogenous compounds of the urine. The within-day and between-day repeatabilities were in all cases less than 5% and 10%, respectively. Limits of detection were 0.007 microg/ml for diclofenac sodium and indomethacin and 0.035 microg/ml for phenylbutazone, whereas limits of quantitation were 0.02 microg/ml for diclofenac and indomethacin and 0.1 microg/ml for phenylbutazone.

Semi-automated solid-phase extraction procedure for the high-performance liquid chromatographic determination of alinastine in biological fluids.

A solid-phase extraction (SPE) method for sample clean-up followed by a reversed-phase HPLC procedure for the assay of alinastina (pINN) in biological fluids is reported. The effects of the sample pH, composition of the washing and elution solvents and the nature of the SPE cartridge on recovery were evaluated. The selectivity of SPE was examined using spiked rat urine and plasma samples and the CH and PH cartridges gave rise to the cleanest extracts. The recoveries obtained in spiked rat urine and plasma samples were 91.2+/-2.7 and 99.9+/-2.8%, respectively. The proposed SPE method coupled off-line with a reserved-phase HPLC system with fluorimetric detection was applied to the quantitation of alinastine in real rat urine samples. The analytical method was also applied and validated for the determination of alinastine in dog plasma. The recovery from spiked dog plasma samples using the PH cartridge was around 65%. The within-day and between-day precisions were 7 and 12%, respectively. The detection and quantitation limits in dog plasma were 0.024 and 0.078 microg/ml, respectively.

Kinetics and mechanism of amitraz hydrolysis in aqueous media by HPLC and GC-MS.

Degradation processes of amitraz in aqueous media have been studied by spectrophotometry, HPLC and GC-MS. Amitraz undergoes hydrolysis reactions at any pH, but towards the acidic pH range hydrolysis proceeds at a faster rate. Depending on the pH value, different products of the hydrolysis have been identified. The main degradation products are 2,4-dimethylaniline at very acidic pH values (pH<3), N-(2,4-dimethylphenyl)-N'-methylformamidine and 2,4-dimethylphenylformamide at less acidic media (pH 3-6) and 2,4-dimethylphenylformamide at basic pH. The mechanisms of the different hydrolysis processes have been elucidated.

Solid-phase extraction with liquid chromatography and ultraviolet detection for the assay of antidepressant drugs in human plasma.

A solid-phase extraction (SPE) method for sample clean-up followed by a reversed-phase high-performance liquid chromatography (HPLC) procedure for the assay of five antidepressant drugs (trazodone, doxepin, desipramine, maprotiline and imipramine) is reported. The drugs were recovered from plasma buffered at a suitable pH using C18 Bond-Elut cartridges and mixtures of methanol-aqueous buffer as washing and elution solvents. The recoveries of the drugs using other sorbent materials (C8, C2, cyclohexyl, cyanopropyl and phenyl Bond Elut and copolymer HLB waters cartridges) were also examined. The selectivity of SPE was examined by using spiked plasma samples and the CH cartridge gave rise to the cleanest extracts. Cyclohexyl cartridges were conditioned successively with 2 ml of methanol and 1 ml of acetic acid-sodium acetate buffer (0.1 M, pH 4.0). Plasma sample was buffered at pH 4.0 and then applied to the sorbent. The washing step was performed subsequently with 1.5 ml of acetate buffer (0.1 M, pH 4.0), 100 microl of acetonitrile and 1 ml of methanol-acetate buffer (30:70, v/v). Finally, the analytes were eluted with 0.5 ml of methanol-acetate buffer (70:30, v/v). The extract was evaporated to dryness, reconstituted in mobile phase, and chromatographed on a reversed-phase C18 column with ultraviolet detection at 215 nm. The recoveries of trazodone, doxepin, desipramine, maprotiline and imipramine from spiked plasma samples using the CH cartridge were 58 2, 84 3, 83 3, 83 3 and 82 2%, respectively. The within-day and between-day repeatabilities were lower than 6% and 9%, respectively. The linearity of calibrations for the five antidepressants was between 0.005 and 2 microg/ml. The limits of detection were 1 ng/ml for trazodone, doxepin and desipramine and 2 ng/ml for maprotiline and imipramine.