Signal staircase

Potential-excitation signals and voltammograms for (a) normal pulse polarography, (b) differential pulse polarography, (c) staircase polarography, and (d) square-wave polarography. See text for an explanation of the symbols. Current is sampled at the time intervals indicated by the solid circles ( ). 

This method was developed further by superimposing the square-wave signal onto a staircase signal [20,21]. Some of the possible potential-time waveforms are shown in Fig. 1.7. Usually, each square-wave cycle occurs during one stair-... 

Fig. 1.8 Scheme of the square-wave voltammetric excitation signal, st starting potential, Esv, pulse height, AE potential increment, t staircase period, to delay time and 7f and 4 denote the points where the forward and backward currents are sampled, respectively... 

This chapter analyzes the subtractive techniques Differential Multipulse Voltammetry (DMPV), Differential Staircase Voltammetry (DSCVC), and Square Wave Voltammetry (SWV). Of these, the most employed SWV will be analyzed in more detail. Interesting alternatives to DSCVC and SWV are Differential Staircase Voltcoulometry (DSCVC) and Square Wave Voltcoulometry (SWVC), which are based on the analysis of the difference of converted faradaic charge signals obtained between two successive potential pulses when a staircase potential or a square wave potential is applied [4, 5], which is very useful for the study of surface-confined redox species. There exists, however, a book in this series devoted entirely to the theory and application of SWV [6], so in some of the reaction mechanisms analyzed, the reader will be directed to this title for a more thorough treatment of the SWV response. 

The VCD calculated for this model polymer is shown in Figure 3, and resembles that observed for the decamer sequence d(CG)5, both in overall spectral appearance and signal magnitude (cf. Section 5). Thus, the simplistic "spiral staircase" model appears to be a good starting point for the qualitative interpretation of the experimental data. 

Current step— The excitation signal used in controlled current techniques in which the potential is measured at a designated time [i]. See also - chronopotentiometry, -> cyclic chronopotentiometry, - staircase voltammetry. Ref. [i] Heineman WR, Kissinger PT (1984) In Kissinger PT, Heine-man WR (eds) Laboratory techniques in electroanalytical chemistry. Marcel Dekker, New York, pp 129-142... 

Technique applied to measure the chemical diffusion coefficient of the intercalating species within insertion-host electrode materials with the help of an electrochemical cell, followed by the current response on the staircase potential signal that is recorded as currenttime curve [i]. The theory of this technique is based on... 

The signal from staircase voltammograms can be further analyzed by - Fourier transformation and analysis of the frequency domain data [iv]. 

Figure 23-21 Generation of a square-wave voltammetry excitation signal. The staircase signal in (a) is added to the pulse train in (b) to give the square-wave excitation signal in (c). The current response At is equal to the cuirent at potential I minus that at potential 2.

In linear potential scan (LSV) and cyclic (CV) voltammetries, a potential varying linearly with time is applied between an initial potential, usually at a value where no faradaic processes occur, and a final potential (LSV) or cycled between two extreme (or switching) potential values at a given potential scan rate v (usually expressed in mV/sec). In other techniques, such as normal and differential pulse voltammetries (NPV and DPV, respectively), or square-wave voltammetry (SQWV), the excitation signal incorporates potential pulses to a linear or staircase potential/time variation. 

---