Fast-scan voltammetry

In this example, the rate of a fast cleavage reaction was determined by a combination of low-temperature and fast-scan voltammetry [24]. Upon insertion of an electron into a v/c-dinitro compound, the resulting radical anion undergoes rapid C-N bond cleavage to form nitrite ion and a p-nitroalkyl radical, which in turn undergoes further reduction. 

The addition of an electromagnetic shield to the body of the tip can greatly reduce the stray capacitance. This is particularly useful for fast-scan voltammetry [54] and high frequency impedance experiments [55],... 

These considerations highlight the fact that microdialysis and voltammetry, particularly fast-scan cyclic voltammetry, estimate two quite different aspects of DA transmission characterized by different temporal and spatial constants. Microdialysis estimates steady-state levels of extracellular DA and changes in these levels taking place on a minute scale away from DA release sites. Fast-scan voltammetry estimates changes in DA-like signals taking place on a subsecond scale near DA release sites. 

A recent study by Xi et al. (1998) utilized single carbon fiber instead of multiple fiber electrodes and a fast-scan voltammetry instead of chronoamperometry. An additional difference was that the rats were first trained to acquire stable rates of heroin selfadministration and then were implanted with the electrodes. Under these conditions 60% of the rats responded to self-injection of 0.06A).l mg/kg of heroin with a monophasic increase, 20% with a biphasic increase/decrease and 20% with a biphasic decrease/ increase of the electrochemical signal (Xi et al., 1998). Only monophasic increases were observed with doses of 0.2 mg/kg of heroin. Tonic monophasic increases in signal were observed also by chronoamperometry with stearate-coated electrodes in a comparative study of cocaine and amphetamine self-administration in parallel with microdialyis (Di Ciano et al., 1995). From this study, however, it appears that, although the effect of drug self-injection on dialysate DA and on the tonic voltammetric signal is qualitatively... 

Robinson DL, Venton BJ, Helen MLAV, Wightman RM. Detecting sub-second dopamine release with fast-scan voltammetry in freely moving rats. CUn Chem 2003 49 1763-73. 

Electroanalyhcal techniques (also in combination with other techniques, e.g., ophcal techniques such as photometry and Raman spectrometry) can be employed to inveshgate many functional aspects of proteins and enzymes in particular. It is possible to study the biocatalytic process with respect to the chemistry of the active site, the interfacial and intramolecular ET, slow enzyme achva-tors or inhibitors, the pH dependence, the transport of tlie substrate, and even more parameters. For example, slow scan voltammetry can be used to determine the relation of ET rates or of protonation and ligand binding. In contrast, fast scan voltammetry allows the determination of rates of interfacial ET. In addition, it is also possible to investigate chemical reactions that are coupled to the ET process, such as protonation. The use of direct ET for mechanistic studies of redox enzymes was recently reviewed by Leger and Bertrand [27]. Mathemahcal models help to elucidate the impact of different variables on the enhre current signal [27, 75, 76]. 

Fast scan voltammetry, in particular on microinterfaces, can be used for determination of charge-transfer rate constants. Impedance analysis can be used not only in analytical applications, but also to obtain a better understanding of surface phenomena (48) and adsorption (32). Microinterfaces, with their high own resistance, are well suited for impedance analysis derived from measurements of noise generated by electrochemical systems (49, 50). Understanding the phenomena peculiar to microinterfaces is essential to future studies of the electrochemistry of small domains. 

Quantitative investigations of the kinetics of these polymerization a-coupling steps have been performed by fast-scan voltammetry on ultramicroelectrodes in order to estimate the lifetime of the transient species. The rate constants for the dimerization of thiophene are greater than 10 M s, while the lifetime of oligothiophene radical cations increases with chain length the rate constant for unsubstituted thiophene tetramer is close to 10 and that of the pentamer is below 10 M s [18]. These studies have... 

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]. 

Fast-scan voltammetry has largely been developed for biological applications [50,52], and employs scan rates up to kV s . It has also been used for the detection of various anions and cations on submillisecond timescales [32, 53-56]. 

Hsueh, C.C. Brajter-Toth, A. (1993). Fast-scan voltammetry in aqueous solutions at carbon fiber ultramicroelectrodes with on-line iR compensation. Analytical Chemistry, 65, 1570-1575. 

The standard reduction potential, the heterogeneous rate constant, and the transfer coeiUcient obtained from the CVFIT program are shown in Table 6-1. For repetitive experiments, and for different scan rates, the fitted parameters show only small variations. This is a good indication both that the mechanism is correct and that the parameters obtained are meaningful and not the result of local minima. Furthermore, the reduction potential is consistent with that measured under similar conditions by fast scan voltammetry. It is also... 

Baur JE, Kristensen EW, May LJ, Wiedemaim DJ, Wightman RM (1988) Fast-scan voltammetry of hiogenic amines. Anal Chem 60 1268-1272. 

Electrochemical detection is generally carried out in one of two modes fast-scan voltammetry or constant potential amperometry [3]. The characteristic voltammograms of different neurotransmitters obtained by fast-scan voltamme-... 

---