Pulsed Voltammetry Techniques

Square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are used for both qualitative and quantitative analysis. These methods take advantage of computer timing to repeatedly sample current signals at two points relative to the time of application of a square wave voltage signal to the electrode. The difference between the two current values is plotted as a function of the applied DC potential. The resultant is peaks rather than voltammetric waves, corresponding to the electroactivity of the species in the electrochemical cell. The major component of this difference current is the faradaic current, which flows due to an oxidation or reduction at the electrode surface. The capacitive or charging current component, due to electrical charging of electrode double layer, is largely eliminated. This increases the signal to noise ratio (versus comparable DC methods). Trace analyses of metallic ions and of organic pharmaceutical compounds are common applications for these pulse techniques.

The difference in the two techniques is in the detail of the applied potential pulsed waveform. The square wave applied waveform is shown below.

Differential pulse has the following applied waveform.

Background

The sensitivity of these techniques is adjusted by changing the pulse width and pulse period. Since the current response to each pulse is like the chronoamperometry experiment, the longer the pulse width the longer the current has to decay and since the current is sampled toward the end of the pulse width the sampled current will be smaller. This relation can be used to improve the sensitivity.

Experiment for square wave or differential pulse voltammetry

Experimental Conditions:

Square wave parameters used in the example shown below:

Run scans in the 10 mM and 5 mM Ferrocyanide solutions and compare the peak heights and peak areas. The results obtained using the 66-CS1200 Computer-Controlled Electrochemical System are shown below.

Using the data analysis software included in the 66-CS1200 analysis of the peak height and area of the two results are given below. As the results show, the peak height and peak area track the concentration changes in the Ferrocyanide solutions.

The differential pulse technique will give similar results.

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