Analytical method for the determination of urinary 3-phenoxybenzoic acid in subjects occupationally exposed to pyrethroid insecticides

The determination of urinary 3-phenoxybenzoic acid enables exposure to pyrethroid insecticides to be evaluated. A method for the quantitative determination of this metabolite in urine is described. The compound and the internal standard (2-phenoxybenzoic acid) are derivatized with pentafluorobenzylbromide and transformed into pentafluorobenzyl esters, which are determined by gas chromatography with an intermediate polarity capillary column and an electron-capture detector. Before GC analysis, the urinary extracts are purified on LC-Si SPE columns. The proposed method has a detection limit of 0.5 μg/l and a mean recovery of 91.3%. The coefficient of variation of the analytical procedure, evaluated at a concentration of 24.96 μg/l, was 9.58%. Storage of the urine samples for 3 months at −18°C did not lead to significant changes in the concentration of analyte. The method was tested analysing the urine of a farm worker with symptoms of pyrethroid poisoning, occupationally exposed to esfenvalerate.