Cathode-ray Polarography with Rapid-dropping Mercury Electrodes

Abstract

LINEAR sweep cathode-ray polarography with the dropping mercury electrode has developed in two distinct lines: single sweep polarography^1–3 in which the applied potential change is impressed on the electrodes once in the lifetime of each mercury drop, and multisweep polarography^4–6 in which it is applied several or many times. The latter is electronically the simpler, but the former possesses distinct advantages and is in more general use. In order to ensure that the drop surface area does not change appreciably during the electrode reaction, it is necessary, in the case of single-sweep working, to synchronize the application of the potential with the latter part of drop life. In earlier instruments this is achieved by using a multivibrator with fixed ‘rest’ and ‘sweep’ periods and arranging for the sharp decrease in current, which occurs when a drop detaches, to trigger the instrument back to its ‘rest’ condition while growth of the next mercury drop takes place. Later instruments^7,8 use a more satisfactory arrangement by which the drop is detached by the application of an electromechanical pulse to the electrode capillary at the conclusion of the potential sweep.