Ac Polarography and its application to overcome the problem of Dc polarographic maxima in the study of complex ions

Dc polarograms of many species electro-active at the dropping mercury electrode exhibit marked maxima which make the theoretical analysis of the current/voltage curve difficult. For studies on complex ions of the electro-active species a knowledge of reversible half-wave potentials and diffusion currents is required. These parameters cannot conveniently and reliably be evaluated from polarograms exhibiting maxima and to make any useful calculations, gelatin or other maximum suppressors must be added. The technique of using a maximum suppressor is however unsatisfactory in the study of complex ions, as electrode reactions are frequently altered by its addition. More satisfactory approaches are here suggested, using ac polarographic methods. The chloride complexes of Bi(III) and Sb(III) have been investigated, as both these electrode reactions exhibit pronounced maxima in chloride media. Further difficulties in the use of the polarographic method of evaluation of the chloride complexes of these systems are discussed in detail. Four complexes were found for both systems and the values of the stability constants are reported.