Pulsed differential voltammetry

Selectivity Selectivity in voltammetry is determined by the difference between half-wave potentials or peak potentials, with minimum differences of+0.2-0.3 V required for a linear potential scan, and +0.04-0.05 V for differential pulse voltammetry. Selectivity can be improved by adjusting solution conditions. As we have seen, the presence of a complexing ligand can substantially shift the potential at which an analyte is oxidized or reduced. Other solution parameters, such as pH, also can be used to improve selectivity. 

The difference between the various pulse voltammetric techniques is the excitation waveform and the current sampling regime. With both normal-pulse and differential-pulse voltammetry, one potential pulse is applied for each drop of mercury when the DME is used. (Both techniques can also be used at solid electrodes.) By controlling the drop time (with a mechanical knocker), the pulse is synchronized with the maximum growth of the mercury drop. At this point, near the end of the drop lifetime, the faradaic current reaches its maximum value, while the contribution of the charging current is minimal (based on the time dependence of the components). 

Differential-pulse voltammetry is an extremely useful technique for measuring trace levels of organic and inorganic species, hi differential-pulse voltammetry, fixed-magnitude pulses—superimposed on a linear potential ramp—are applied to the working electrode at a time just before the end of the drop (Figure 3-5). The current... 

FIGURE 3-5 Excitation signal for differential-pulse voltammetry. 

Molecular Characterization It has been repotted that o-qulnones oxidize ascorbic acid In homogeneous solutions (25). Surface qulnones have also been reported to exist on activated carbon surfaces (16). However, cyclic voltarammetry Is not sufficiently sensitive to allow an unambiguous Identification of the reversible wave ascribed to surface qulnones (16). Therefore, differential pulse voltammetry (DPV) and square wave voltammetry were employed. 

Figure 4, Differential pulse voltammetry of a freshly polished, activated glassy carbon surface (a) and a digital simulation of the DPV (b). The pulse frequency vas2 Hz with an amplitude of 10 mV. The DC scan rate was 2 mV s...

The redox potentials of the ITO electrodes modified with CgoN -MePH clusters were measured by cyclic voltammetry and differential pulse voltammetry in the absence and presence of magnetic processing. 

Differential pulse voltammetry has been widely used for in vivo electrochemical analysis This technique combines the linear sweep and pulsed potential... 

Differential pulse voltammetry provides greater voltammetric resolution than simple linear sweep voltammetry. However, again, a longer analysis time results from the more sophisticated potential waveform. At scan rates faster than 50 mV/sec the improved resolution is lost. Because it takes longer to scan the same potential window than by linear sweep, an even longer relaxation time between scans is required for differential pulse voltammetry. 

To increase the mass transfer rate, Tokuda et al. [7] carried out normal and differential pulse voltammetry at micropipettes and extracted the rate constant values within the... 

CSDPV Cathodic stripping differential pulse voltammetry... 

Tacussel and their application by Gonon et al.148 to differential pulse voltammetry (DPV) and differential normal pulse voltammetry (DNPV) in vivo, also called the biopulse technique the microelectrodes are implanted in the living animal brain and variations in the concentrations of some molecules can be followed via the Tacussel PRG 5 and BIPAD instruments (see also the selection of commercial models in Table 3.4). 

Phase-sensitive detection is not at all specihc for EPR spectroscopy but is used in many different types of experiments. Some readers may be familiar with the electrochemical technique of differential-pulse voltammetry. Here, the potential over the working and reference electrode, E, is varied slowly enough to be considered as essentially static on a short time scale. The disturbance is a pulse of small potential difference, AE, and the in-phase, in-frequency detection of the current affords a very low noise differential of the i-E characteristic of a redox couple. 

Competitive immunoassays may also be used to determine small chemical substances [10, 11]. An electrochemical immunosensor based on a competitive immunoassay for the small molecule estradiol has recently been reported [11]. A schematic diagram of this immunoassay is depicted in Fig. 5.3. In this system, anti-mouse IgG was physisorbed onto the surface of an SPCE. This was used to bind monoclonal mouse anti-estradiol antibody. The antibody coated SPCE was then exposed to a standard solution of estradiol (E2), followed by a solution of AP-labeled estradiol (AP-E2). The E2 and AP-E2 competed for a limited number of antigen binding sites of the immobilized anti-estradiol antibody. Quantitative analysis was based on differential pulse voltammetry of 1-naphthol, which is produced from the enzymatic hydrolysis of the enzyme substrate 1-naphthyl phosphate by AP-E2. The analytical range of this sensor was between 25 and 500pg ml. 1 of E2. 

The electrochemical response of analytes at the CNT-modified electrodes is influenced by the surfactants which are used as dispersants. CNT-modified electrodes using cationic surfactant CTAB as a dispersant showed an improved catalytic effect for negatively charged small molecular analytes, such as potassium ferricyanide and ascorbic acid, whereas anionic surfactants such as SDS showed a better catalytic activity for a positively charged analyte such as dopamine. This effect, which is ascribed mainly to the electrostatic interactions, is also observed for the electrochemical response of a negatively charged macromolecule such as DNA on the CNT (surfactant)-modified electrodes (see Fig. 15.12). An oxidation peak current near +1.0 V was observed only at the CNT/CTAB-modified electrode in the DNA solution (curve (ii) in Fig. 15.12a). The differential pulse voltammetry of DNA at the CNT/CTAB-modified electrode also showed a sharp peak current, which is due to the oxidation of the adenine residue in DNA (curve (ii) in Fig. 15.12b). The different effects of surfactants for CNTs to promote the electron transfer of DNA are in agreement with the electrostatic interactions... 

It has been demonstrated that the presence of CNTs greatly increases the oxidation peak current of 6-benzylaminopurine. The CNT-modified electrode is suitable for the determination of trace amounts of benzylaminopurine and has the advantages of high sensitivity, quick response, and good stability [86], Wang et al. have studied the electro-catalytic oxidation of thymine at a a-cyclodextrin incorporated CNT coated electrode in an alkaline media. A sensitive detection scheme for thymine has been further developed by using differential pulse voltammetry [87], The electrochemical determination... 

Other techniques that have been used include subtractive differential pulse voltammetry at twin gold electrodes [492], anodic stripping voltammetry using glassy-carbon electrodes [495,496], X-ray fluorescence analysis [493], and neutron activation analysis [494],... 

Electrochemical preconcentration can be achieved in the following two different ways, depending on whether differential pulse stripping voltammetry (differential pulse ASV) or adsorption differential pulse voltammetry has been applied. 

Sipos et al. [89] used subtractive differential pulse voltammetry at a twin gold electrode to determine total mercury levels in seawater samples taken from the North Sea. 

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