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.

Catalytic and Kinetic Waves in Polarography

“…Thus, using Breyer's method (applying at the electrode, together with a dc potential, a superimposed small sinusoidal potential, and making the ac component independent of the linearly increasing dc electrode potential [250][251][252]) the electrode process of U (VI) reduction to U (V) was investigated, with disproportionation of U(V) to U(VI) and U(IV) [253]. The current measured by Breyer's method seems to be the sum of the active and capacitance component and therefore cannot be quantitatively evaluated; the results obtained by this method are only qualitative.…”

A METHOD OF RECORDING a-c. POLAROGRAMS ON A CONVENTIONAL d-c. POLAROGRAPH

“…The a-c. polarography of a lumber of ions has been studied by Breyer, Gutman, and Hacobian (5,6,8,9). Cations were found to produce normal waves while the a~liolls studied (9) produced very sharp anodic waves whose summit potentials did not correspond to their E ; values but instead appeared a t potentials a t which discharge began.…”

Alternating current polarographic determination of electroactive species more negatively reduced than the major compponent

“…Iron (III), for instance, was shown to interfere with the reduction of tin(II) (3). Oxygen is reduced more positively than cadmium(II), indium(II), lead(II), and thallium(I) and certainly would interfere with the determination of these latter species (3)(4)(5)(6) if normal ac polarographic procedures are used.…”

“…Available evidence (3,4,8) in fact indicates that with low concentrations of the more positively reduced species, no interference arises in many cases. However, no experimental data appear to be available for the case where ac polarography should be extremely advantageous, that is, for a vast concentration excess of the more positively reduced species where dc polarography cannot be used at all.…”