Pulsed potential

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

Methods employing individual linear or triangular pulses (potential-sweep, triangular pulse and cyclic voltammetry, sometimes also called... 

Determination of lead in 70 pL samples of whole blood can be carried out in a few minutes by a procedure including treatment with a matrix-modifying solution containing hydrochloric acid, Hg(II) ions, Triton X-100 and Bi(III) as internal standard. After deposition of lead amalgam on a glassy carbon electrode by a pulsed potential cycle, analysis... 

A study was made of RP-HPLC with constant-potential (1.2 V vs SCE) and pulsed-potential amperometric detection using platinum or gold electrodes, of the derivatives of the common amino acids, obtained from phenyl and methyl isothiocyanates. All the thiohydantoins (98) were oxidized at both electrodes LOD was less than 0.2 pM for lysine and glycine, for 50 pL injection268. 

It is used in IC systems when the amperometric process confers selectivity to the determination of the analytes. The operative modes employed in the amperometric techniques for detection in flow systems include those at (1) constant potential, where the current is measured in continuous mode, (2) at pulsed potential with sampling of the current at dehned periods of time (pulsed amperometry, PAD), or (3) at pulsed potential with integration of the current at defined periods of time (integrated pulsed amperometry, IPAD). Amperometric techniques are successfully employed for the determination of carbohydrates, catecholamines, phenols, cyanide, iodide, amines, etc., even if, for optimal detection, it is often required to change the mobile-phase conditions. This is the case of the detection of biogenic amines separated by cation-exchange in acidic eluent and detected by IPAD at the Au electrode after the post-column addition of a pH modiher (NaOH) [262]. 

Hoogvliet et al. [9] have proposed a pulsed-potential pretreatment procedure, which allows one to decrease, in a reproducible manner, surface roughness of mechanically polished polycrystalline gold electrodes by a factor of 2. 

Once the differences between both types of potential perturbation are clarified, a question arises about the nature of potential-controlled techniques attending to the nature of the perturbation, are they pulse potential or step potential techniques If the pulse definition is applied in a strict sense, only Single Pulse Voltammetry is a true pulse technique (see Scheme 2.1), whereas the rest of double and multipotential techniques are indeed multistep techniques (see Sects. 4.1, 5.1 and 7.1). 

Eqs. (5.12)—(5.15) show that the boundary value problem has the same general form for any pulse potential p, whatever the geometry of the electrode. 

In this section, the current-potential curves of multi-electron transfer electrode reactions (with special emphasis on the case of a two-electron transfer process or EE mechanism) are analyzed for CSCV and CV. As in the case of single and double pulse potential techniques (discussed in Sects. 3.3 and 4.4, respectively), the equidiffusivity of all electro-active species is assumed, which avoids the consideration of the influence of comproportionation/disproportionation kinetics on the current corresponding to reversible electron transfers. A general treatment is presented and particular situations corresponding to planar and nonplanar diffusion and microelectrodes are discussed later. 

Amperometric 1 x10-9g 2 x 104 Responds to -OH functionalities Used for alphatic and aromatic -OH compounds, amines, and indoles pulsed potential units are most sensitive, can be used with gradient elution and organic mobile phases senses compounds in oxidatitive or reductive modes mobile phases must be highly pure and purged of 02... 

Analytical glow discharges have conventionally operated with a constant negative dc potential applied to the cathode. There is no reason, however, that they can t be operated through the application of a pulsed potential, an applied rf potential, or a positive potential applied to the cathode. Many variations have been tried alone and in combination with one another. Perhaps the most interesting among these (because of the unique capabilities that it provides) is the radio-frequency-powered discharge. The analysis of nonconductors is covered extensively in a later chapter, but a brief overview is in order here. 

Other forms of voltammetry are as follows (1) fast-scan cyclic voltammetry useful in neuroelectrochemistry (2) nanosecond voltammetry for a 5-pm disk working microelectrode with RC < 1 gs, scan rates of 2.5 MV/s allow for fast kinetics measurements (3) differential-pulse voltammetry with staircase pulses, potential resolutions of 0.04 V and detection limits of 10 8M can be attained (4) anodic (cathodic) stripping voltammetry traces... 

Based on cathodic electrodeposition of Ti02 and W03 films, de Tacconi and coworkers (2003) provided a method to cathodically electrodeposit Ti02/W03 composite films via the control of a pulsed deposition potential. By mixing the deposition baths for both Ti02 and W03, the authors applied a pulsed potential... 

Fig. 18.4 Contrast between TiC /WCE composite films electrodeposited by (a) pulsed-potential deposition in a single deposition bath and (b) sequential deposition in different baths [reprinted from Somasundaram et al. (2006), copyright (2006), with permission from Elsevier]...

The detector can be made to function in two ways either a constant potential is applied across the sensor electrodes (the DC mode) or a pulsed potential is used (the pulsed mode). In the DC mode, a constant electrode potential of a few volts is employed that is just sufficient to collect all the electrons that are produced and provide a small standing current. If an electron capturing molecule (for example a molecule containing a halogen atom which has only seven electrons in its outer shell) enters the sensor, the electrons are captured by the molecules and the molecules become charged. The mobility of the captured electrons are much reduced compared with the free electrons and, furthermore, are more likely to be neutralized by collision with any positive ions that are also generated. As a consequence, the electrode current falls dramatically. 

In the pulsed mode of operation, which is usually the preferred mode, a mixture of methane in argon is usually employed as the carrier gas. Pure argon can not be used very effectively as the carrier gas as the diffusion rate of electrons in argon is ten times less than that in a 10% methane-90% argon mixture. The period of the pulsed potential is adjusted such that relatively few of the slow negatively charged molecules reach the anode, but the faster moving electrons are all collected. 

In the case of silver deposition, the OCP was —680 mV versus SCE after deposition, the nucleation pulse potentials Ej and the deposition time tj and t2 were varied. The growth pulse potential E2 was -700 mV versus SCE. The averaged diameter of the silver cluster deposited was about 200 nm. The samples with particles were taken from the preparation bath and carefully washed and dried in a desiccator. 

The electrodeposition of gold was made in an acidic electrolyte of 0.005 M HAUCI4 per liter. The open circuit potential (OCP) after deposition was +820 mV versus SCE. The pulse potentials were varied between +800 and +600 mV versus SCE. Particles between 10 and 500 nm diameter were prepared. 

The electropolymerization of ferrocene/thiophene conjugates [65] was conducted by oxidation on a Pt electrode and led to the deposition of a monolayer of poly (thiophene). The electropolymerization was performed from several solution systems, such as tetrabutylammonium hexafluorophosphate/acetonitrile and lithium perchlorate/acetonitrile, at a concentration of 0.1 M. Constant potential experiments (+ 2.0 V) for a definite time were used to effect polymerization. Polymerization was also attempted using cyclic voltammetry (repeatedly sweeping from 0.0 to + 2.5 V) and pulse potential (potential stepped from 0.0 to 2.0 V and back to 0.0 V). 

Pulsed amperometry in a three-electrode detector cell is carried out in a non-flowing solution, in which solute ions are dissolved in the supporting electrolyte. A pulsed potential is applied and is increased stepwise after each pulse. The resulting current... 

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