Colorimetric Determination of Tyrosine BY G. CERIOTTI AND L. SPANDRIO

The procedure described permits quantitative application of the Sakaguchi reaction. The greatest advantage of the method is the stability of the coloured product in butanol. The sensitivity, already high in the original method, is further increased, since the volume of the final coloured solution is reduced by the extraction. For concentrations of arginine ranging between 0-5 and 6 ,ug./ml. there is a linear relationship between quantity and colour yield and there is good reproducibility. The variability of the older method introduced by variability in the quality of urea, by nitrogen-bubble formation, by condensation on cuvettes and by rapid decrease of colour intensity is avoided. These factors are so important that each constitutes a serious obstacle to the quantitative application of the older methods. The empirical variations of hypobromite concentrations from one test to the other, suggested by Sakaguchi (1948), are also avoided. This is particularly important, as variations in hypobromite concentrations have a considerable effect on the colour yield. The a-naphthol-diacetyl reaction in the presence ofpropanol, performed by the method of Rosenberg et al. (1956), is undoubtedly an improvement over the original Sakaguchi (1925a, b; 1948, 1950, 1951) method, but it is less sensitive than the present method and less reproducible. In the present method the colour develops immediately, and then shows no significant change for a long time; the influence of temperature is also limited.