DETERMINATION OF STABILITY CONSTANTS OF COORDINATION COMPLEXES BETWEEN CADMIUM(Ⅱ) ION AND GLYCINE BY DIFFERENTIAL PULSE POLAROGRAPHY

The polarographic peak potential and peak current of coordination complexes formed between Cd(Ⅱ) and glycine at different pH values of the reaction system,having its Cd(Ⅱ) ion concentration maintained in the range of 5.00×10-5-2.00×10-4mol·L-1,and the ratio of concentrations of glycine to Cd(Ⅱ) ion kept in the range of 100 to 400,were measured by differential pulse polarography.Based on the relationship curve on the variation of peak potentials with the variations of pH of the reaction solution and of the concentration of Cd(Ⅱ)-ion (in thems of lg Cd),a rational model of the metal ion coordination complex was established.By using the optimum computer program,and by solving the mass equilibrium equation of the reaction system,and by fitting the formation curves of the metal coordination complexes tested,the stability constants (lg β) of the five species of coordination complexes.MHL,ML,ML2,ML3 and ML2(OH) were obtained giving values of 9.67±0.15,4.35±0.02,7.83±0.03,10.04±0.04 and 11.48±0.13 respectively.