Determination of mixtures of urinary benzoic, 3- and 4-methylbenzoic, and mandelic acids by gas chromatography.

The determination of benzoic, 3- and 4-methylbenzoic, and mandelic acids in urine by gas chromatography (G.C.) is presented. The analytical procedure includes: addition of internal standard (beta-naphthol), alkaline hydrolysis, ethyl ether extraction, evaporation of the solvent, and silylation of acids with Silyl-8 in pyridine (1:1). The results are calculated from ratios of the internal standard and determined metabolites peak surface areas. The coefficient of variation of the method in determination of mentioned acids is +/- 8%.