Effect of Inorganic Salts on the Determination of Serum Alubmin by Dye-Binding Method with Absorbance Decrease

Dye-binding methods based on protein error for determining human serum albumin are classified into two methodologies via measurements of the absorbance increase under an acidic condition (absorbance increase method) and the absorbance decrease in a pH region near the neutral condition (absorbance decrease method). The color development of protein in the absorbance increase method is known to be affected by the pH, and the concentrations of dye, buffer and coexisting anions in the samples. However, the effect of coexisting anions on color development in the absorbance decrease method is unclear. In the present work, the effect of an inorganic salt on color development in the absorbance decrease method was investigated by a calculation based on the chemical equilibrium of the protein error and an experiment, and was compared with the results of the absorbance increase method. By adding an inorganic salt, the absorbance was decreased. The degree of its decrease was smaller in the absorbance decrease method than in the absorbance increase method, and differed according to the kind of inorganic salt. The experimental results agreed well with those obtained by a calculation.