New biuret reagent for the determination of proteins in cerebrospinal fluid.

HE BIURET REACTION has become an important analytic procedure for rapid and accurate determinations of protein concentrations in biologic fluids. Since the initial reports of Riegler (1), Autenrieth and Mink (2), and Autenrieth (3), who showed that proteins react with alkaline copper solutions to yield a violet-blue color, many modifications have appeared to improve the stability of alkaline copper solutions and to define optimal conditions for the reaction. These studies have resulted in biuret procedures for serum protein that yield results equivalent to those obtained by micro-Kjeldahl analysis (4-9). In applying the biuret procedure (10) to cerebrospinal fluid protein determinations, we observed that some undiluted fluids become sufficiently turbid to invalidate the analyses. Initial experiments indicated that the turbidity could be prevented by the addition of a chelating agent, disodium ethylenediamine tetraacetate (EDTA) to the biuret reagent. The results of this study and the development of a new copper reagent form the basis of this report.