Effect of anion concentration on the stability of the uranyl-ascorbate complex

Abstract The effect of anion concentration and the dependence of uranyl ascorbate on the nature of anion present is systematically studied for nine different anions over the concentration range (0.2–2.0) × 10 −2 M . These anions, commonly encountered in pharmaceutical preparations with ascorbic acid (vitamin C) are nitrate, sulfate, chloride, bromide, fluoride, phosphate, citrate, oxalate, and tartrate. Based on the absorbance data, and on the value of the replacement constant K calculated, the studied anions may be arranged according to their complexing power on uranium as follows: citrate > tartrate > phosphate > oxalate > fluoride > sulfate > nitrate > chloride > bromide. This order is substantiated by the calculated values of the side reaction coefficients α M of the uranyl ligand complex or the conditional stability constant of uranyl-ascorbate calculated at different ligand concentrations.