ELECTROCHEMICAL-BEHAVIOR OF MORDANT RED-19 AND ITS COMPLEXES WITH LIGHT LANTHANIDES

Mordant Red 19(MR19) is reduced at mercury electrode at -0.67 V vs. Ag /AgCl with two electrons per molecule in Ph 9.2 buffer by differential pulse polarography and linear sweep voltammetry. The peak potential i s dependent on the Ph of solution. The exhaustive electrolysis, howeve r, gives 4 electrons per molecule because of the disproportionation of the unstable hydrazo intermediate. The electrochemical reduction of l anthanide-MR19 complexes is observed at more cathodic potental than th at of free ligand. The difference in peak potentials between complex a nd free ligand varies from 75 Mv for La3+ to 165 Mv for Tb3+ and incre ases with increasing the atomic number of lanthanide. The electrochemi cal reduction of lanthanide complexes with MR19 is due to the reductio n of ligand itself, and it can be potentially useful as an indirect me thod for the determination of lanthanides. The shape of i-E curves and the scan rate dependence indicates the presence of adsorption and the adsorption was confirmed by potential double-step chronocoulometry an d the effect of standing time. Also the surface excess of the adsorbed species and diffusion coefficients are determined. The composition of the complex is determined to be 1: 2 by spectrophotometric and electr ochemical methods.