Complexation of Calcium by α-Isosaccharinic Acid under Alkaline Conditions

Abstract

The complexation of Ca2+ by α-isosaccharinic acid (α-ISA) was determined by measuring the solubility of Ca(α-ISA)2 as a function of pH. In the pH range between 12 and 12.8, the observed increase of the total concentration of Ca in solution with increasing pH is explained by the complexation reaction: Ca2+ + α-ISA- ⇋ Ca(α-ISA-H)0 + H+ with log KoCaISA0= -10.4 (s = 0.2) at I = 0. In addition to this complexation reaction, another complex is postulated: Ca2+ + α-ISA- ⇋ Ca(α-ISA)+ with log KoCaISA+ = 1.70. A value for the solubility product of Ca(α-ISA)2 is calculated: log Kosol = -6.36 (s = 0.1) at I = 0.