Chronoamperometry with linear sweep

Both linear sweep voltammetry (oscillographic polarography, stationary electrode polarography, chronoamperometry with linear sweep) and chrono-potentiometry have been extensively applied for studies in molten salts. The advantages of linear sweep voltammetry include (1) extensively developed theory enabling the experimentalist to interpret the mechanisms of relatively complex electrode reactions (2) well-defined mass transfer conditions, particularly when faster scan rates ( 1 V/sec) are employed (3) the decrease of the faradaic charge with the square root of the scan rate and the resulting decrease of any modifications of the solid electrode caused by the faradaic process. Chronopotentiometry, 29) related electroanalytical... 

The majority of measurements for electroanalysis with microelectrodes are recorded under steady-state conditions by using either chronoamperometry (CA), linear sweep voltammetry (LSV) or cyclic voltammetry (CV) [1,2, 9,10]. Moreover, to solve problems related to the selectivity between species with similar redox potentials, pulsed techniques such as differential pulse voltammetry (DPV) [1, 7, 43 5] and square-wave voltammetry (SWV) [1, 45-49] have been employed. The use of the latter technique also minimizes the influence of oxygen in aerated natural samples [47]. In order to enhance sensitivity in these measurements, fast-scan voltammetry (FSV) [50] or the accumulation of analytes onto an electrode surface has also been performed, in conjunction with stripping analysis (SA) [51]. 

The simple linear-sweep voltammetry (LSV) or linear potential sweep chronoamperometry (of which polarography with a dropping Hg electrode is the earliest example) can be understood simply if one looks at just the first rise to a peak in Fig. 11.70. 

The cyclic voltammogram (CV) of (C5gN)2 showed three overlapping pairs of reversible one-electron reductions within the solvent window ( i = -997 mV, E2 = -1071 mV, 3 = -1424 mV, 4=-1485 mV, E = -1979 mV, g = -2089 mV ferrocene/ferrocenium couple, internal standard) [7]. A combination of linear sweep voltammetry and chronoamperometry estabUshed that all overlapping waves were two-electron reductions [ 120]. There was also an irreversible two-electron oxidation with a peak potential at -i- 886 mV, that is 0.2 V more negative (easier to oxidize) than Cgo [121]. The appearance of closely spaced pairs of waves in the CV was interpreted in terms of two (identical) weakly interacting electrophores, similar to the dianthrylalkanes [122]. After the third double wave, the process is irreversible, this was interpreted as irreversible cleavage of the dimer bond. 

Differential pulse voltammetry (DPV) is essentially an instrumental manipulation of chronoamperometry. It provides very high sensitivity because charging current is almost wholly eliminated. More important for CNS applications, it often helps to resolve oxidations which overlap in potential. The method combines linear potential sweep and square-wave techniques. The applied signal is shown in Fig. 16A and consists of short-duration square-wave pulses (<100 msec) with constant amplitude (typically 20 or 50 mV) and fixed repetition interval, superimposed on a slow linear potential scan. The Fapp waveform can be generated with a laboratory-built potentiostat, but most DPV work is done with a commercial pulse polarograph (see Appendix). The inset of Fig. 16A shows an enlargement of one pulse. The current is measured just before the pulse... 

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