Simultaneous determination of parathion and metabolites in serum by HPLC with column switching

A new high-performance liquid chromatographic method with column-switching has been developed for the simultaneous determination of parathion and its metabolites such as p-nitrophenol and paraoxon in serum. Serum samples were injected onto a precolumn packed with LiChroprep RP-8 after simple dilution with 20% phosphoric acid. Polar plasma components were washed with 0.02 M phosphate buffer (pH 3.0). After valve switching, the concentrated compounds were eluted in back-flush mode and separated on a Ultracarb ODS 30 column with a gradient of acetonitrile - 0.01 M phosphate buffer (pH 3.0) as mobile phase. The method showed excellent precision, accuracy and speed with detection limit of 0.1 μg mL^-1. Total analysis time per sample was < 40 min and coefficients of variation for intra-and inter-assay were < 4.5 %.