Differential pulse voltammetry
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Differential pulse voltammetry is a kind of electrochemical measurement. It can be considered as a series of regular voltage pulses superimposed on a linearly changing voltage, in which the resulting current is measured between the ramped baseline voltage and the pulse voltage. A digital staircase voltage is commonly used as the ramped baseline.
By contrast, in normal pulse voltammetry the current resulting from a series of ever larger potential pulses is compared with the current at a constant 'baseline' voltage. Another type of pulse voltammetry is square wave or square pulse voltammetry, which can be considered a special type of differential pulse voltammetry in which equal time is spent at the potential of the ramped baseline and potential of the superimposed pulse.
These measurements can be used to study the redox properties of extremely small amounts of chemicals because of the following two features:
(1) In these measurements, the effect of the charging current can be minimized, so high sensitivity is achieved.
(2) Faradaic current is extracted, so electrode reactions can be analyzed more precisely.
Differential pulse voltammetry has these characteristics:
(1) Reversible reactions show symmetrical peaks, and irreversible reactions show asymmetrical peaks.
(2) The peak potential is equal to E1/2r-ΔE in reversible reactions, and the peak current is proportional to the concentration.
(3) The detection limit is about 10-8 M.
The system of this measurement is usually the same as that of cyclic voltammetry. The potential between the working electrode and the reference electrode is changed as a pulse from an initial potential to an interlevel potential and remains at the interlevel potential for about 5 to 100 milliseconds; then it changes to the final potential, which is different from the initial potential. The pulse is repeated, changing the final potential, and a constant difference is kept between the initial and the interlevel potential. The value of the current before and after the pulse are sampled and their differences are plotted versus potential.
