Differential pulse polarograph of nickel(i1) with imidazole and related compounds

Electrochemical reductions of nickel(II) complexes with imidazole, histamine, histidine, and pilocarpine have been studied using differential pulse polarography in the presence of 1.0 mol dm^-1 sodium acetate as supporting electrolyte. The peak potential for the complexes appeared at more positive potentials than for the nickel aquo ion. The positive shift ceases and then reverses to the negative direction for high ligand concentrations. Both histidine and pilocarpine have shown another wave which may be ascribed to the catalytic reduction of hydrogen ions in the solution. The peak height of the differential pulse pre-wave Increases with the concentration of the ligands only when shift in potential is in the positive direction with the nickel ion concentration in excess of the organic ligand. The linearity of variation of the peak height with the concentration for the above mentioned compounds has been investigated. A mixture of histamine and histidine showed two separate peaks, permitting possible simultaneous determination when the compounds are in admixture.