The recording of D.C. Polarographic waves and the measurement of the instantaneous current at the end of the life of the mercury drop

Abstract

Because of the slowness of response of the current detectors used in the infancy of polarography, it has become the custom to measure the average current rather than the instantaneous current at some given time near the end of the life of the mercury drop. McKenzie (1958a) has pointed out that there are a number of theoretical advantages to be gained by measurement of instantaneous diffusion current. The work reported in the present paper shows that this measurement can be made accurately with conventional electronic equipment. Owing to the inherent lag in automatic recording polarographs which measure average current, it is not possible to obtain from the records the half-wave potential and slope with good accuracy. It is shown that the advantages of automatic recording and accuracy in determining the half-wave potential and slope may be realized by recording instantaneous current-voltage curves. Also abnormalities in current-time curves may be readily detected. Apparatus using a conventional recorder and a preamplifier which is a modification of that of Kelley and Miller (1952) is described. A device which can be used to control pen drive is also described.