A method for the determination of gentisic acid in serum.

The recent trials of gentisic acid as a therapeutic agent (1, 2)’ stimulated our interest in the development of methods for the determination of gentisic acid in serum. Meyer and Ragan (1) referred to a method which is suitable for the analysis of gentisic acid in urine. No details were given. Although they were able to detect 5 y of hydroquinone per ml. in urine (l), they did not find detectable amounts of this substance in the sera of patients who were receiving large doses of sodium gentisate. We investigated a number of reagents which gave colors with phenols, hydroquinones, and aromatic compounds in general. The color reaction with a mixture of ferric chloride and ferrous chloride was selected as being the most simple and rapid, and a satisfactory method with this reagent was developed. While this method was in the process of development, Camelin et al. (2) reported the analysis of gentisic acid in the serum and the urine by a calorimetric method with ferric chloride after extraction with ether. However, we had found that ferric chloride alone is difficult to use for quantitative measurement of gentisic acid, principally because of rapid fading of the color. These authors do not mention whether they had this difficulty or how it was circumvented if they did.