Gas Chromatographic Determination of Urinary o-Cresol for the Monitoring of Toluene Exposure

A sensitive and reproducible gas chromatographic procedure for the quantitative determination of urinary o-cresol is described. The first step involves acid hydrolysis (2N HCl, 100 degrees C, 10 min), which yields unconjugated o-cresol. After extraction (methylene chloride, pH 2), the organic layer is concentrated by evaporation and samples are analyzed by gas chromatography-flame ionization detection with a DB-5 column (30 m x 0.25 mm, 0.25 microns). Initial oven temperature is set at 30 degrees C for 12 min and the increased 2 degrees C/min to 93 decrees C. 3,4-Dimethylphenol is used as the internal standard. The detection limit of the method is 0.36 mumol/L (1 microL injection). Additional validation data were obtained by analysis of urine samples collected from volunteers exposed to various concentrations of toluene: 10, 20, 30, 50, and 100 ppm over 7 h. Urinary o-cresol concentrations (0-3, 3-7, 7-24, and 0-24 h) were highly correlated with toluene exposure.