Determination of protein by its enhancement effect on the Rayleigh light scattering of carboxyarsenazo

This is the first report on the determination of proteins based on the inte raction with carboxyarsenazo (CAA) by Rayleigh light scattering (RLS). At p H 4, the weak RLS of CAA can be enhanced greatly by the addition of protein s, resulting in three characteristic peaks. Rased on this, the interactions of CAA with nine kinds of proteins were studied and a new quantitative det ermination method for proteins has been developed. This method is very sens itive (0.10-15.3 mu g ml(-1) for bovine serum albumin (BSA)), rapid (< 2 mi n), simple (one step), tolerant of most interfering substances, and gives a close value to that of the Coomassie brilliant blue (CBR) method in the de termination of proteins in human serum. Thus, the CAA assay can be useful f or routine analytical purposes and may overcome some of the limitations of other currently employed methods. Mechanism studies show that the three RLS peaks correspond to the absorption valleys of the CAA-protein complex. (C) 1999 Elsevier Science B.V. All rights reserved.