A Modification of Sakaguchi’s Reaction for the Quantitative Determination of Arginine

The extremely sensitive color reaction given by certain guanidine derivatives with ar-naphthol and sodium hypochlorite, which was observed by Sakaguchi (1925), has been extensively employed as a qualitative test for arginine. The greatest obstacle in a quantitative application of this reaction is its slow rate of color development with the probable destruction of some of the guanidine group by the hypochlorite. When sodium hypobromite is employed instead of sodium hypochlorite, the color development with arginine is practically instantaneous, although calorimetric readings are not possible, since the color begins to fade immediately and almost disappears in 10 minutes. However, the addition of urea immediately after the color development has taken place stabilizes the color sufficiently to permit calorimetric comparisons. This modification of Sakaguchi’s reaction is being studied because of its possible application to the calorimetric determination of arginine and certain other guanidine derivatives. While our studies are not as complete as those made by Poller (1926) on Sakaguchi’s reaction, we found that arginine, glycocyamine, and methylguanidine give an intense red color with this modified reaction; while creatine, creatinine, urea, glycocyamidine, guanidine, and as-dimethylguanidinel do not give any color reaction. No compounds have been found that give the characteristic