Fluorimetric determination of creatine.

STRONGLY ALKALINE SOLUTIONS ninhydrin (1,2,3 indantrione hy) combines with guanidine, monosubstituted guanidines, and disubstituted guanidines to form highly fluorescent addition ucts (1). This reaction has been used as the basis for a simple, itive fluorimetric method for the determination of creatine in m, blood, and urine. he most widely used methods for determining creatine are based n the conversion of creatine to creatinine by heating in the prese of strong mineral acids and subsequent determination of the tinine by the alkaline picrate reaction of Jaffe (2). The reaction not specific for creatinine, and many naturally occurring subces give a similar color. The method has been criticized also bese of the formation of noncreatinine chromogens and loss of tine during heating. Many modifications of the alkaline picrate hod have been proposed, but none has completely eliminated these ctions (3). reatine can be measured directly by the Barritt modification of Voges-Proskauer reaction (4). This reaction is not specific for tiiie since other naturally occurring guanidine compounds give a ilar, although less intense, color with diacetyl. Sulfhydryl comnds interfere with color development and must be removed (5). erson et at. (5) have used the diacetyl reaction for the determina-