Complexation of Ni(II) by α-isosaccharinic acid and gluconic acid from pH 7 to pH 13

Nickel reactions with gluconic acid (Gl) and α-isosaccharinic acid (ISA) have been investigated from pH 7 to pH 13.3. Measurement of the stoichiometries of the products of these reactions showed that NiGl and NiISA were formed at pH <7, Ni2Gl(OH)3 and Ni2ISA(OH)3 were formed at pH values between 7 and 10 and Ni2Gl(OH)4 and Ni2ISA(OH)4 were formed at pH >10. The stability constants for the formation of the soluble complexes were measured using an ion exchange resin method (Schubert method) at pH 7 and 13.3, and differential pulse polarography at pH 7. The polarographic measurements were performed in order to check the validity of the Schubert method at pH 7. This was due to the possibility of any cationic complexes that may have been formed sorbing to the resin. The importance of determining the stoichiometry of the reactions before calculating the stability constants from measurements taken using the Schubert method is emphasised.