Analytical Sciences

Influence of pH for the Determination of Serum Albumin by a Dye-binding Method in the Presence of a Detergent

Yuji SUZUKI

Department of Health Sciences, School of Health and Social Services, Saitama Prefectural University, 820 Sannomiya, Koshigaya, Saitama 343-8540, Japan

In the dye-binding method, the absorbance increase caused by a protein error of a pH indicator is observed only in a restricted pH range. However, this pH range in the presence of a detergent has not yet been examined. Thus, the author investigated the pH (pH_UL) where the absorbance increase becomes zero by a calculation based on the chemical equilibrium of a protein error of a pH indicator, and by experiments using four sulfonephthalein dyes. The pH_UL value changed only with the detergent concentration, but did not change at all due to the dye, buffer solution or protein concentrations. Although the pH_UL value was different according to the kind of dye used, it correlated well with the pK_D values (dissociation constant) of BPB, BCG, BCP and BTB. The characteristics of pH_UL in the reactions of the four dyes indicated good agreement with that obtained by a calculation.

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