The Polarography of the Nickel(II)-Glycinate Complexes

Abstract

The nickel-glycine system showed three polarographic waves (Fig.1). The first and the second waves were observed at about-1.0 and -1.2 V vs. SCE, respectively when the glycine concentration was relatively low in a pH range from 5 to 8. As the glycine concentration increases, above the pH value of 8 the first wave disappeared and the third wave appeared at -.5 V. These three waves correspond to the reduction of nickel-glycinate complexes 1: 1, 1: 2 and 1: 3, respectively.
The second wave of nickel-glycinate complexes gave a kinetic current based on the dissociation reaction of Ni(gly), - to Ni(gly)2. The rate constant of the dissociation reaction was determined by means of Koryta's equation from the observed kinetic current and the stability constant of the Ni(gly)3- (log K3 = 3.21 from the pH titration). The value of the rate constant was 1.6 x 10 secl, at ionic strength of 0.1 and at 25±0.1°C, independent of hydrogen ion concentration.