A colorimetric method for the determination of citric acid in blood and plasma.

As early as 1897 the oxidative bromination of citric acid to form a brominated acetone derivative, presumably principally pentabromoacetone, was adapted to the quantitative determination of citrate (1). Most subsequent procedures have been based on the same reaction. Among the more recently described procedures are those of Pucher (2) and of Goldberg and Bernheim (3). These methods, with minimum sensitivities of approximately 0.05 and 1.0 mg. of citric acid, respectively, are not sufficiently sensitive for many purposes; hence experiments were undertaken to develop a more sensitive procedure. In common with earlier procedures the method reported herein is based on the formation of a brominated acetone derivative. The sensitivity, however, has been lowered to 5 to 50 y of citric acid by the use of a new procedure for the calorimetric microdetermination of bromide. Since this work was completed, a method for citric acid determination with a sensitivity of 10 to 60 y of citric acid has been published by Taussky and Shorr (4). This method, which also is based on the oxidative bromination of citric acid, appears satisfactory. The present procedure, however, is presented, as it differs considerably in the method used for the determination of the bromine present as brominated acetone derivatives.