Green Fluorescence of Guanidinium Compounds with Ninhydrin

Abstract

CURRENTLY available methods for the determination of creatine and other guanidinium compounds are based on non-specific chromogenic reactions. These include the Jaffe, the diacetyl α-naphthol, the Sakaguchi, and the sodium nitroprusside–potassium ferrocyanide reactions. Determination of the individual members of the guanidinium group requires chromatographic separation, chemical degradation, or specific enzymatic destruction of the compound. In a search for a more satisfactory reaction for detection of guanidinium compounds than is at present afforded by chromogenic reactions we have found that ninhydrin (1,2,3-indantrione hydrate) in strongly alkaline media forms highly fluorescent products with guanidine and monosubstituted or N,N-disubstituted guanidines. The most highly fluorescent product is formed with creatine, which can be determined in concentrations as low as 0.07 µgm./ml.; other guanidinium compounds form less fluorescent products.