Protein error of pH indicators in the presence of detergents.

The characteristics of color development due to a protein error in the dye-binding method in the presence of a non-ionic detergent has been investigated by the calculations based on the chemical equilibrium of a protein error. The calculation results were compared with those obtained using three pH indicators (Bromophenol Blue, Bromocresol Green and Bromocresol Purple) and three non-ionic detergents in the pH region from 1 to 13. In the experiments, the color development increased with the lower concentrations of the detergents, but decreased at higher concentrations. The pH where the color development reached a maximum value shifted to a higher pH as the detergent was added. These experimental results were reproduced by the calculation when the molar absorptivity of the dye-protein complex was assumed to increase due to adding the detergent. Such agreement between the experimental and the calculated results indicates that the characteristics of the color development in the dye-binding method in the presence of a non-ionic detergent can be analyzed by calculations based on the chemical equilibrium of a protein error.