The Metachromasy of Tetrabromophenolphthalein Ethyl Ester Anion Caused by Inorganic Salts

Abstract

The effect of inorganic salts on the color of tetra4romophenolphthalein ethyl ester anion (TBPE anion) has been studied using a photometric technique. The color of a 13 μM aqueous solution of TBPE anion changed to red violet from blue violet at pH 6.80 by addition of inorganic salts. The order of the effect on the absorbance change at 590 nm was NaClO₄<LiCl<KCl, and NaCl<NH₄Cl<MgCl₂_??_CaCl₂. The TBPE anion concentration depen dency of the spectrum in 2.44M CaCl₂ suggests the association of TBPE anion. The temperature dependency of the spectrum in 3.9M NaCl supported this idea. The spectrum change of TBPE anion induced by the addition of protamine was quite similar to those observed by the addition of inorganic salts. It is concluded that the color change of TBPE anion by inorganic salts is not caused by salting-out but by metachromasy.