Comparison of Differential-Pulse and Variable-Amplitude Pseudoderivative Normal-Pulse Polarography with Microprocessor-Based Instrumentation

A comparison of differential-pulse (dp) polarography and variable-amplitude pseudoderivative normal-pulse (pdnp) polarography Indicates that the two techniques are nearly Identical for reversible and irreversible electrode processes. The approach to the pseudoderivatization when Implemented with microprocessor-based instrumentation is different from that previously described In that data points obtained from a normal pulse (np) polarogram a fixed number of data points (millivolts, ∆E) apart are sequentially subtracted under software control. Since the pseudoderivative is obtained after the experiment has been completed, results for variable amplitudes of ∆E may be obtained from one experiment. ∆E from the pdnp experiment may be equated with the pulse amplitude in dp polarography. The essential difference between the two techniques Is that the dp response still contains dc terms which distort the curve leading to undesirable features in some circumstances. Although a static mercury-drop electrode Is used to demonstrate experimentally the important features of pdnp, the approach yields similar results at a conventional dropping mercury electrode. For electrode reactions which involved adsorption or film formation where np polarography is already superior to dp polarography, the pdnp method Is considerably superior to dp polarography. In light of the results obtained here, variable-increment pdnp polarography Is considered to be the preferred approach to pulse polarography.