Use of computerized instrumentation for pseudo-derivative direct current and normal pulse polarography with correction for charging current

The application of computerized instrumentation to pseudo-derivative d.c. and normal pulse polarography is described. Calculation of background current by means of a linear least-squares fit of data obtained prior to the rising part of the sigmoidal d.c. or pulse curve and extrapolation to other potentials enables close to the faradaic response to be obtained over wide concentration ranges. After subtraction of background current, least-squares fitting of the sigmoidal curve enables data smoothing to be undertaken and other calculations to be performed. Pseudo-derivative curves obtained by plotting current differences obtained from corrected and smoothed data provides limits of detection comparable to those of more sophisticated polarographic methods. The reduction of cadmium in 1 M NaCl is considered because it occurs at potentials near the electrocapillary maximum where charging current correction is most difficult. The limits of detection are 10^-7 M for the pseudo-derivative d.c. method, and 10^-3 M for the pulse method.