Negative AC Polarographic Waves-Phase-selective Polarograms

Abstract

In an earlier publication, we drew attention to and explained the phenomena of "negative" ac polarographic waves and of complex-shaped waves with both negative and positive portions. These, as was shown, need not be due to particular electrochemical properties of the relevant system under scrutiny (or even to instrumental errors), but may arise simply from the vectorial combination of the various impedances that make up an electrochemical cell. In that publication, we dealt only with normal, total-component ac polarographic curves. Since then, we have built an ac/dc potentiostatic polarograph based on the paper of Brown, Smith and Booman and in using it have found that, when recording phase-selective polarograms, one obtains markedly negative waves for the 90.K-phase component at far lower frequencies than in normal, total-component polarography. We have investigated this with some computer calculations and report the results here. Negative waves as described are likely to be encountered more and more frequently in view of the increasing use of phaseselective ac instruments.