High-pressure liquid chromatographic determination of toluenein urine as a marker of occupational exposure to toluene

Objective: To establish a convenient method by high-pressure liquid chromatography (HPLC) to measure toluene in urine as a marker of occupational exposure to toluene. Methods: As soon after sampling as possible, 1 ml of urine was mixed with an equal volume of acetonitrile in a 2.2-ml HPLC glass bottle, and the bottle was tightly sealed and stored at 4 °C. Immediately before HPLC determination, 100 μl methanol was added to the mixture to prevent confounding effects of glycosuria, and the bottle was spun to remove any suspended matter. An aliquot of the supernate was introduced into the HPLC system and analyzed on a PRODIGY column, with an acetonitrile – perchloric acid – phosphoric acid – water mixture serving as the mobile phase. The effluent was monitored at 191 nm. Results: The method can measure toluene in urine every 20 min; the detection limit was 2 μg/l, the coefficient of variation was less than 5%, and the recovery rate was 100%. No significant reduction in toluene concentration was observed for 1 week after storage at 4 °C. When the method was applied to end-of-shift urine samples from 13 male workers exposed to toluene at 18–140 ppm and also to urine samples from 10 nonexposed male controls, toluene in urine was linearly related to toluene exposure concentration, with a regression line passing close to the origin. The correlation coefficient was as high as 0.97 (n = 23). No toluene was detected in control urine samples. Calculations suggest that urinary toluene accounts for as little as less than 0.01% of the toluene absorbed via inhalation and that the absorbed toluene is converted almost quantitatively to hippuric acid and, by less than 0.1%, to o-cresol. Received: 25 August 1997 / Accepted: 13 February 1998