Determination of Hippuric Acid in Urine by GC/MS: in vivo Metabolism of Toluene to Hippuric Acid on Toluene Poisoning

This paper describes the use of the stable isotope tracer method for the metabolism from toluene to hippuric acid to help an assessing biological monitoring at low level exposure of toluene. This analytical method was applied to Wistar rats with poisoning of toluene during two weeks period, and was used to determine the urinary levels of endogeneous hippuric acid-d0 and exogenous hippuric acid-d5 which is produced from toluene-d8 in vivo, after intra-peritoneal administration of toluene-d8. It was possible to detect an alteration in the excretion of urinary hippuric acid compared with the control using deuterium-labeled toluene as a stable isotope tracer to distinguish its metabolite from endogeneous metabolite. We suggest that the in vivo metabolic investigation of the biological monitoring for hippuric acid should be based on the stable isotope method, and that the method was effective for the measurement of low exposure concentrations.