Direct photometric determination of globulin in serum.

A convenient method for direct photometric determination of total globulin in serum has been developed using a one-tube, one.reagent system. The analysis is based on a variation of the Hopkins-Cole reaction, in which glyoxylic acid condenses with the tryptophan residues present in globulin to produce a purple color. In the presence of copper and under the conditions of the analysis, color intensity is proportional to serum globulin concentration. The method is standardized with either a serum control or a suitable tryptophan derivative (e.g., acetyl-DL-tryptophan). There is little or no interference from free tryptophan, albumin, bilirubin, lipemia, or mild hemolysis. The precision of the method is ±3% (95% confidence limits), and results agree with those obtained by the salt fractionation method of Wolfson et at. [Amer. J. Gun. Pathol. 18, 723 (1948)]: t -0.88; critical t = 2.02; 95% confidence limits.