PubMed · 7403271
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M Awschalom, F H Attix. 1980. A-150 plastic-equivalent gas.. https://doi.org/10.1088/0031-9155%2F25%2F3%2F019
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A highly sensitive high-performance liquid chromatographic method with electrochemical detection (HPLC-ED) was developed for the determination of isoflavones. Electrochemical behaviour of daidzein and genistein was studied on carbon paste electrode (CPE) by adsorptive transfer stripping square wave voltammetry. The obtained electrochemical results were used for the development of HPLC-ED method. Furthermore, isoflavones were separated on an Atlantis dC18 column using a mobile phase consisting of acetonitrile (solvent A) and 0.15M acetate buffer of pH 5.5 (solvent B) at a flow rate 0.4 mL/min. A linear gradient profile (solvent B) was at 0-2 min 87%; 22 min 60%; 27 min 50%; 31 min 45%; 47 min 87%. Full scan of multi-channel coulometric detection was tested and optimal potential at 450 mV was chosen for our purposes. Calibration curves were linear (daidzein R(2) = 0.9993 and genistein R(2) = 0.9987). The detection limit for daidzein/genistein was 480/394 pg/mL (1.8/1.5 nM) and per column 2.4/1.9 pg. Isoflavones extracted from soybean products (farina, meat, milk) by the accelerated solvent extraction (ASE) procedure and isoflavones present in human urine were determined by the HPLC-ED method.
A previously described method of measurement of malondialdehyde (MDA) in human urine after derivatisation with 2,4-dinitrophenylhydrazine (DNPH) was tested for a possibility of using methyl malondialdehyde (MeMDA) as an internal standard. Despite structural similarity, those compounds were found to produce different yields of derivatisation under the same conditions depending on urine matrix. We conclude, that MeMDA is not suitable as an internal standard for the measurement of MDA in urine under previously reported conditions when DNPH is used as a deriviatising agent.
A high-throughput method for quantitative determination of methadone enantiomers in human plasma was developed and validated by liquid chromatography/tandem mass spectrometry. The effects of pH and of types and concentrations of mobile-phase modifiers on the enantioselectivity of (R)- and (S)-methadone were investigated on a Chiral-AGP column. A baseline separation of the enantiomers was achieved with a retention time of less than 5 min. Ionization suppression and other matrix effects were evaluated. Morphine, cocaine, 6-monoacetylmorphine, benzoylecgonine and ecgonine methyl ester did not interfere with the performance of the assay. The specificity, linearity, intra- and inter-assay precision and accuracy, and extraction recovery were fully evaluated. The method showed excellent reproducibility (overall coefficient of variance < 8%) and accuracy (overall bias < 2.7%) with a broad linear range. The enantiomers were stable in human plasma after five freeze-thaw cycles, under bench-top storage at room temperature (RT) for 6h, in the extract reconstitution solution at RT for 17 h, and in processed-extracts stored at RT for 142 h. This validated LC/MS/MS assay offers high-throughput and improved specificity, sensitivity, linear range and ruggedness over previously published methods and has been successfully applied to the analysis of clinical samples.