A COMPARISON OF THE DETERMINATION OF STABILITY CONSTANTS OF COMPLEXES OF Cd(Ⅱ)WITH AMINO ACIDS AND SIMPLE PEPTIDES USING MICRO—pH—METRIC TITRATIONS AND CYCLIC VOLTAMMETRY

This paper reports the determination of stability constants for complexes of Cd(Ⅱ)with Gly,Ala,Val,Asp,Gly—Asp,Asp Gly,Gly—Gly and Gly—Gly—Gly using both micro—pH—metric titra-tions and the application of convolution—deconvolution cyclic voltammetry at 25℃ and I=0.10 mol·dm~(-3)(KNO_3).Stability constants were calculated from pH—metric data using the SUPERQUAD com-puter program and cyclic voltammograms were collected,stored and manipulated using the EG and GCONDECON 300 software.A considerably larger ligand:metal ratio(e,g.50:1)was possible usingvoltammetry.Evaluation of results from the two techniques suggests that stability constants for thespeciesCdL_2]andCdL_3]are reliable when calculated fromvoltammetry while those forCdL]are morereliable when determined by pH-metric titration.