Colorimetric method for hippuric acid.

FTIPPURIC ACID 1S an important metabolic product normally present in urine in amounts determined by tile ingestion of benzyl-containing foods and medicinals (ii). Because this compound is comparatively inert chemically, identification requires isolation and the determination of physical constants after extensive purification. There has long been need for a reliable and sensitive color reaction for its detection and for estimation of low-level concentrations. In attempts to enhance chromatographic separations of components in acidic extracts of urine through preparation of benzoyl and related derivatives, development of a deep-red color with benzenesulfonyl chloride (BSC) in the presence of pyridine (Py) was traced to hippuric acid (HA) in the mixture. Studies of the reaction led to a sensitive color test applicable for quantitative measurements. Other alkyl and aryl acid halides failed to develop significant colors and amino acids and related acidic compounds did not react in the test. Salicyluric acid is equally sensitive and probably other amido acids are a source of interference. Confirmation of HA is readily made following positive findings for an amido structure in the test.