Interference by ammonium sulphate with the estimation of proteins by the biuret reaction

Abstract

THE procedure of Gornall, Bardawill and David1 is widely used for the estimation of proteins, the only frequent modification being adjustment of the volumes to permit mixing of reagents and reading of the extinction directly in the cells of a spectrophotometer. Gornall, Bardawill and David 1 state that 'ammonium ion is a disturbing factor in the biuret reaction', but provide no quantitative data. Some information on the interference has been provided by Henry, Sobel and Berkman2; but these workers used two biuret reagents of different composition and instead of a pure protein used serum as a standard. The extent of the interference of ammonium ion with the biuret reaction does not appear to be widely known. Thus, Dixon and Webb3 claim that "few of the non-protein materials likely to be present affect the estimation, and it is particularly useful because it is insensitive to ammonium salts". © 1963 Nature Publishing Group.