Staircase voltage ramp

Square wave voltammetry achieves increased sensitivity and a derivative peak shape by applying a square wave superimposed on a staircase voltage ramp. With each cathodic pulse, there is a rush of analyte to be reduced at the electrode surface. During the anodic pulse, reduced analyte is reoxidized. The voltammogram is the difference between the cathodic and the anodic currents. Square wave voltammetry permits fast, real-time measurements not possible with other electrochemical methods. 

Pulse voltammetry — A technique in which a sequence of potential pulses is superimposed to a linear or staircase voltage ramp. The current is usually measured at the end of the pulses to depress the - capacitive (charging) current. Depending on the way the pulses are applied and the current is sampled we talk about - normal pulse voltammetry, reverse pulse voltammetry and - differential pulse voltammetry. Several other, less popular pulse techniques are offered in commercial voltammetric instrumentation. Some people consider - square-wave voltammetry as a pulse technique. 

Figure 17-12 Voltage profiles for voltammetry (a) linear voltage ramp used in vitamin C experiment (b) staircase profile for sampled current polarography. Inset (c) shows how faradaic and charging currents decay after each potential step.

Two recent developments in the measurement technique have resulted in a major reduction in the charging current. Firstly, with the introduction of digitally controlled instruments, the linear voltage ramp applied to the electrodes has been replaced with a stepped (staircase) waveform. The voltage... 

A relatively large square wave signal of amplitude A p = 50 mV is superimposed on a stepped voltage ramp (staircase) with voltage steps of about 10 mV. The duration of the square wave... 

---