I A sensitive and reproducible gas chromatographic procedure for the quantitative determination of urinary o-cresol is described. The first step involves acid hydrolysis (2N HCI, 100~ 10 rain), 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 ram, 0.25 pro). Initial oven temperature is set at 30~ for 12 rain

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... then increased 2~ to 93~ 3,4-Dimethylphenol is used as the internal standard. The detection limit of the method is 0.36 I~mol/L (l-pL 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.