Direct colorimetric determination of hippuric acid in urine.

In 1963 Umberger and Fiorese (1) introduced a colorimetric method for HA,1 based on the color reaction of HA, dissolved in anhydrous pyridine, with BSC. Therefore, for applying their method to determine HA in urine, HA must first be extracted from the urine. We found that HA dissolved in water-pyridine (1:1, by vol) produces a red-orange color when BSC is added at room temperature. The absorption spectrum of the color shows only one maximum, at 410 nm, and is quite different from that of the color given by the method of Umberger and Fiorese (1). By adapting the color reaction, we developed a direct and sensitive colorimetric method for determination of HA in urine, which follows the Beer-Lambert law to at least 1 mg/mI of water or urine.