Measurement of direct currents and pulse components for analytical evaluation of differential pulse polarography and voltammetry

Abstract

Simple and inexpensive modifications to differential pulse poiarographs enable the dc and pulse components of the experiment as well as their differences to be measured. Using examples of electrochemically reversible and irreversible electrode processes, as well as kinetically complicated ones, demonstrates that access to additional data usually ignored in differential pulse polarography and voltammetry can be a valuable aid in analytical evaluation of the techniques and in methodology development. Theoretical studies would also appear to be substantially aided by access to such measurements.Differential pulse polarography has become one of the most commonly used methods of polarographic analysis. Originally developed by Barker ( I ) , the technique uses a waveform consisting of a fixed amplitude pulse superimposed onto a dc ramp. Currents measured in the absence of the pulse are subtracted from currents in the presence of the pulse producing the differential current readout in which hi is plotted against the dc potential to produce a differential pulse polarogram (2). Theoretical work in differential pulse polarography has lagged far behind the analytical applications and it is only recently (3-8) that papers have appeared dealing with anything other than a reversible electrode process with planar diffusion. Use of the reversible theory has led to suggestions for improved instrumental design of the technique ( S I 2 ) . The basis for most of these innovations has been to eliminate residual terms arising from incomplete subtraction of the dc component of the experiment (9). Unfortunately, many electrode processes are not simple reversible diffusion controlled electrode processes and the validity of many of these ideas to the irreversible electrode process, adsorption, maxima, or all other well known phenomena associated with polarography is far from clear.Experimentally, in almost all theory vs. experiment correlations, and indeed in analytical work, the differential pulse polarograms are all that are measured. In view of the fact that the technique measures the difference between the pulse and dc polarogram, it is difficult to understand why the individual components of the experiment are not routinely monitored and results used for optimization in analytical work and particularly in theory vs. experiment correlations. This need has obviously been previously recognized by workers having access to very expensive computerized systems. The almost complete lack of studies in this area can be attributed to a lack of suitable readily available inexpensive equipment.In the present paper, it is demonstrated how simple modifications to existing circuits associated with differential pulse polarographs can enable far more information to be obtained than is conventionally the case. A qualitative survey of the information that can be readily extracted is presented to demonstrate the general use of these data automatically discarded in almost all previous studies using differential pulse (dp) polarography. EXPERIMENTALInstrum...

Current Minimum in Differential Pulse Polarography

“…Taking into account that each DPP signal can be presented in terms of its components (which result from the current sampling at the end of pulse and prepulse periods, respectively) 15,21 insight into their shapes could give some information about the "formal" origin of the minimum that appears as an extension of the reduction signal, i.e. an inverse peak.…”

Multimode triple sampling polarography in the study of amalgamation and sphericity effects at the static mercury drop electrode

“…The drop time was 1500 ms and the other instrumental parameters are given in the text. 6 Not determined.…”

Differential pulse polarography at the static mercury drop electrode

“…Unless otherwise stated the polarographic experiments described here were performed using an EG&G Princeton Applied Research Corp. (PARC) Model 174 polarographic analyzer modified as described previously (5) to provide the output of the pulse and DC components while in the differential pulse mode. An EG&G PARC 374 microprocessor-controlled instrument was used for some experiments.…”