Polarography with Alternating Currents. I. Outline of Theory, Apparatus, and Technique

Abstract

A method of polarographic analysis employing the superposition of a small sinusoidal alternating field of low frequency upon the direct potential applied to the dropping mercury electrode has been further developed. Equations are given for the calculation of the ionic concentration from the alternating current (maximum differential current) at the characteristic " summit potential " (analogous to E+ in conventional polarography). This current is proportional to the concentration of the ion species undergoing discharge. The advantages of the method over conventional polarography can be summarized as follows : (i) A.C. polarography can be carried out in solutions containing dissolved oxygen, i.e. in air. (ii) Tedious curve plotting is substituted by a single current reading at the summit potential which yields directly both the half-wave potential and the concentration of the electro-reducible substance.    (iii) Small amounts of less noble ions can be estimated even in the presence of a large excess of nobler ions. (iv) Polarographic waves only 40 mV. apart are clearly separable. (v) An improved all round reproducibility is obtained. (vi) There is a simplified system of recalibration in case of capillary replacement. vii) The use of a delicate galvanometer is eliminated.