吸光度増加測定に基づく色素結合法による血清アルブミン定量のpH範囲

抄録

In the dye-binding method based on a protein error of a pH indicator, the upper-limit pH (pH_UL) at which an absorbance increase occurs exists. In the present work, the relationship between pH_UL and the buffer concentration in color reagent was investigated by a calculation and an experiment using four sulfonephthalein pH indicators. pH_UL was observed in reactions of all the dyes and human serum albumin; it was not affected by the buffer concentration. In addition, the equilibrium constant did not affect pH_UL, suggesting that it does not change due to the kind of buffer. The pH_UL value was peculiar to each dye, and correlated moderately with the dissociation constants of each dye. The pH_UL changed only according to the ratio (ε_PD/ε_D) of the molar absorptivities between the dye-protein complex (ε_PD) and the dissociated dye anion (ε_D), and shifted to a higher pH due to an increase in its ratio. pH_UL was found to exist only when the ratio of the molar absorptivities was ε_PD/ε_D<1.