Comparison of several methods for the measurement of urinary hippuric acid as an index of toluene exposure.

The levels of hippuric acid in the urine of people exposed to toluene vapour were measured by paper chromatography, direct colorimetry, high performance liquid chromatography and gas chromatography. The control was a similar group not exposed to toluene vapour. The values were analyzed statistically, conversion equations calculated, and the propriety of these equation discussed. Since the three chromatographic methods gave similar values, the measurement of urinary hippuric acid by these methods can be used as an index of toluene exposure. The colorimetric method gave higher levels the chromatographic methods, especially for the urine of people not exposed to toluene. This may have been due to glycine conjugates (other than hippuric acid) developing a similar color, resulting in elevated values for hippuric acid. This colorimetric method should be used with caution for biological evaluation of workers with low toluene exposure.