Abstract
We examined the effects of electrolytes and non-electrolytes on the phenomenon of protein error of pH indicators, such as bromophenol blue and bromocresol green which have been commonly applied to the determination of protein in biological materials. Changes in optical absorbance due to protein error of the pH indicator decreased by the addition of various electrolytes (NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, NH4Cl, Na2SO4,(NH4) 2SO4, MgSO4), but no change of absorbance was observed by the addition of non-electrolytes such as urea and glucose. The effects of different electrolytes on the change of absorbance were identical when the anion of electrolytes was the same. The effects of electrolytes also decreased with the increase in the pH of color reagents and the decrease in the ionic radius of the anion. The phenomenon of the protein error was confirmed to be closely related to the positively charged amino groups in protein molecule and dye anion.
