Resonance Rayleigh-scattering method for the determination of proteins with some monoazo dyes of chromotropic acid.

In a weak acid medium, protein reacts with a monoazo dye of chromotropic acid, such as Chromazol KS (CALKS), Acid Chrome Dark Blue (ACDB), Chrome Blue SE (CBSE), Acid Chrome Blue K (ACBK), Chlorophosphonazo I (CPAI), Arsennazo I (AAI) and Chromotrope 2R (CT2R), to form a combination product. This results in a significant enhancement of the resonance Rayleigh-scattering (RRS) intensity, and the corresponding RRS spectrum appears. The characteristics of the RRS spectra of the combination products and the optimum conditions for the reactions were investigated. The intensity of RRS is directly proportional to the concentration of protein in a certain range. The RRS methods have high sensitivity for the determination of protein, the detection limits for bovine serum albumin (BSA) are 10.0 - 30.2 ng/ml, and the sensitivity order is CALKS > AAI = CPAI > ACBK = CT2R > ACDB > CBSE. The selectivity for CALKS has been examined, and the method was applied to the determination of a microg amount of protein in a synthetic sample with satisfactory results.