Gluconate complexes of Sm(III), Gd(III), Dy(III) and Ho(III)

Gluconic acid (HGI) forms a cationic complex (C2+) with the rare earth metal ions (M3+ = Sm3+, Gd3+, Dy3+ and Ho3+) at low pH which dissociates to C+ and subsequently to C at higher pH. The equilibrium constants for the reactions, M3+ + HGI reversible C2+ + H+, C2+ reversible C+ + H+, C+ reversible C+ + H+ and M3+ + GI- reversible C++H+ are given. (auth.)