To ensure complete removal of nitrate, heating to near dryness and redissolving the residue in 0.1N HCl was repeated twice. Gallium concentration in the stock solutionwas determined by isotope dilution–thermal ionization mass spectrometry. Sodium perchlorate and sodium thiocyanate used were of AR grade from Fluka. The electrolyte mixture of sodium perchlorate containing sodium thiocyanate (4M NaClO4 + 0.5M NaSCN), is referred to as mixed electrolyte in the text and all potentials referred to in the work are with reference to SCE.