Quantitative estimation of salicylic acid and its metabolites by thin-layer densitometry.

A rapid thin-layer densitometric method for the quantitative determination of salicylic acid and its metabolites in urine or plasma is described. The method is specific and very sensitive. Nanogram quantities of salicylic acid and its metabolites, both free and conjugated, may be estimated. Known metabolites, as well as the newly described gentisuric acid, were estimated quantitatively in urine from a patient treated with aspirin.