Determination of salicylic acid and two metabolites in plasma and urine using fluorimetry for directly measuring salicyluric acid.

TLDR: An improved method has been developed for the measurement of salicylic acid and salicyluric acid in blood plasma and for these two substances and Salicyl glycuronates in urine and a higher value than previously reported has been found.

Abstract: An improved method has been developed for the measurement of salicylic acid and salicyluric acid in blood plasma and for these two substances and salicyl glycuronates in urine. Older methods measured salicyluric acid by the different extraction efficiencies of two solvents and the weaker color formation of salicyluric acid with ferric nitrate. This method measures salicyluric acid more specifically by means of its marked fluorescence at p H 10. A low concentration of a fluorescent substance, probably salicyluric acid, which has not been reported previously was found in dog plasma following large doses of sodium salicylate. The rate of hydrolysis of salicyluric acid by concentrated hydrochloric acid, an important factor in the calculation of the salicyl glycuronate fraction in this and former methods, has been re-examined and a higher value than previously reported has been found. An explanation of this difference is suggested. A synthetic sample of the glycuronate of salicylic acid coupled through the phenolic hydroxyl group, which has not been isolated from urine in pure form, has been tested for reactivity in the method.