Clarification and Application of Selectivity for Metal Ion of Ternary System of Aldonic Acid, Boric Acid, and Metal (II) Ion

The complexation equilibria for the binary system of glucosaminic acid (2-amino-2-deoxy-D-gluconic acid) and boric acid and that of glucosaminic acid and metal (II) ion and the ternary system of glucosaminic acid, boric acid, and metal (II) ion have been investigated by potentiometric measurements using Ni (II), Zn (II), Cd (II), and Pb (II) as the metal (II) ions. The structures of the present complexes have been characterized by ^C and ^B NMR.The additional stabilization by forming the ternary systems is the greatest in the Cd (II) system. It is considered that the conformation of the glucosaminic acid in its boric-acid binary systems can distinguish the difference in the ion size. On the other hand, the ternary system with germanic acid instead of boric acid exhibits no selectivity for the metal (II) ions probably due to the adjustment of the geometry of the five-coordinate germanic acid. It is revealed that the Cd (II) complex is more stable than the Pb (II) complex in the ternary system with boric acid while the stability in the glucosaminic-acid binary system is reversed. The development of such a new selectivity arising from the ternary system is the major purpose for the present study. Because it is easy for the ternary complex to dissociate the metal (II) ion by raising the pH value of the solution, the present system is extensively applicable for the separation or concentration of the metal ion in the field of analytical chemistry.