Fundamental Study of Differential Pulse Polarography

Differential pulse pelarography has proved te be a very sensitive technique for trace analysdis. Parry et al. evaluated the theoretical current-potential relationship as a function of pulse amplitude and reported experimental verification of the theory. We have studied the effects of pulse amplitude on peak current and peak half-width, beside the relationship between peak potential and half-wave potential and reexamined in detail the equation derived by them. The equation was found to be applicable for a reversible electrode process with both 3-electrode system and 2-electrode system. It was observed, however, that the experimental values of an irreversible wave did not coincide with the theoretical ones. The peak half-width was larger and the peak current was smaller than that observed for the reversible wave. For the analytical application of the irreversible wave, greater pulse amplitude may increase the sensitivity without practical influence on peak half-width. BTesides its high sensitivity, differential pulse polarography gfferied ope ggvantage of employing very dilute supporting electrolytes. At 10-6mol/l level of reducible species, the peak current obtained in 1 mmol/l supporting electrloyte agreed well with the theoretical value. However, the typical reversible reduction wave of 1 mmol/l Cd(II) in 0.01 mol/l KCl showed a curious behavior quite similar to the irreversible wave in which the peak half-width became smaller than the calculated value at 100 mV pulse amplitude. Under this condition, an approximately linear relationship existed between peak current and pulse amplitude either wite 3electrode system or with 2-electrode system. Moreover, we have examined the influence of scan rate and the concentration of supporting electrolyte on the differential pulse polarographic wave and also evaluated the temperature coefficient of the peak current.