Some Applications of a New Color Reaction for Creatinine

Some years ago it was found by one of us that creatinine reacts with 3,5-dinitrobenzoic acid in alkaline solution to give a purplish rose color, and that the reaction is sufficiently sensitive to permit its application to urine and blood filtrates.’ Particular interest is attached to a new reaction for creatinine because the Jaffe reaction with picric acid has hitherto been the only known highly sensitive reaction for this compound, and because the determination of creatinine is practically wholly dependent upon the use of this single reaction which, as is well recognized, is not highly specific for creatinine. The present paper describes results obtained by the application of the dinitrobenzoic acid reaction to creatinine and to various compounds closely related to it, as well as to urine and blood filtrates. All of the creatinine derivatives and related substances which were studied reacted either positively or negatively to both picric and dinitrobenzoic acids, which indicates a similarity in the mechanism of the two reactions. However, the reaction with dinitrobenzoic acid appears to be somewhat more specific for creatinine, as evidenced by our results with urine and blood filtrates, described below, and by the fact that all of the reactive creatinine derivatives which were studied gave somewhat less color, in terms of creatinine, with the new reagent than with picric acid.