Square wave pulse voltammetry

Besides these potentiometric-based methods, a series of electrochemical techniques can be applied to the detection of biomolecular interactions. Depending on the desired dynamic detection range and the specific properties of the system under study, techniques such as electrochemical impedance spectroscopy, voltage step capacitance measurements, amperometry, differential pulse voltammetry, square wave voltammetry, AC voltammetry, and chronopotentiomet-ric stripping analysis can be used for label-free detection of DNA, proteins, and peptides [1]. Often these techniques require the use of redox mediators. Electrochemical impedance spectroscopy (EIS), in particular, is a very promising technique for DNA biosensing [2,3]. 

The electrochemical sensors with chemical recognition applied to pesticides analyses take advantage of the analytical features of the differential pulse voltammetry, square-wave voltammetry, and stripping voltammetry [26-30], which allow pesticides detection at residues levels. Current efforts are directed toward sensitivity and selectivity improvement by chemical modification of the electrode surface by molecularly imprinted polymers and micro- and nanostructured materials [31]. 

Sampled Current Voltammetry Differential Pulse Voltammetry Square Wave Voltammetry ... 

Electroanalytical methods have been extensively applied in sensing and biosensing. Potentiometry, amperometry, cyclic voltammetry, linear voltammetry, differential pulse voltammetry, square-wave voltammetry, and electrochemical impedance spectroscopy (EIS) represent the most-used electrochemical techniques used for biosensor fabrication and detection. 

Stripping voltammetry involves the pre-concentration of the analyte species at the electrode surface prior to the voltannnetric scan. The pre-concentration step is carried out under fixed potential control for a predetennined time, where the species of interest is accumulated at the surface of the working electrode at a rate dependent on the applied potential. The detemiination step leads to a current peak, the height and area of which is proportional to the concentration of the accumulated species and hence to the concentration in the bulk solution. The stripping step can involve a variety of potential wavefomis, from linear-potential scan to differential pulse or square-wave scan. Different types of stripping voltaimnetries exist, all of which coimnonly use mercury electrodes (dropping mercury electrodes (DMEs) or mercury film electrodes) [7, 17]. 

Determined by direct electrochemistry at a glassy carbon electrode (cyclic, differential pulse, or square-wave voltammetry). 

To appreciate how the analytical sensitivity of polarography and voltammetry can be enhanced by sampling the current, or by pulsing the potential in normal pulse, differential pulse and square-wave pulse methods to attain a lower concentration limit of about 10 mol dm. ... 

Electrochemical Simulation Package (ESP) is a free program which allows a PC to simulate virtually any mechanism by the following pulse techniques, i.e. cyclic voltammetry, square-wave voltammetry, chronoamperometry and sample DC polarography. The program can also be used in conjunction for fitting experimental data at solid and DME electrodes. It is the only package to explicitly claim to be bug-free . 

The detection limit for TLV has been improved substantially by using differential pulse and square-wave voltammetry (Chap. 5). For example, detection limits in the 10 8 M range and below have been demonstrated in thin-layer cells requiring less than 100 /xL of sample [61,62]. One practical application of twin-electrode thin-layer cells is in the automatic electrochromic rearview mirror for automobiles. A cell with optically transparent electrodes is placed in front of a mirrored surface. At night, electrolysis in the cell to generate colored material can rapidly reduce glare from following vehicles. 

The charging current must decay to zero, or be otherwise accounted for, before the analytically useful Faradaic current that results from electron exchange with electroactive species in the sample can be measured and used for calibration. Because the double layer is chaiged by ions that must move through the solution, the time constant for charging is the product of its capacitance (a few JJ.F) and the resistance of the solution (typically 100 Q). Charging can therefore be very fast. This is an important consideration because there is a relationship between the speed with which a current can be measured and the precision and detection limit of the assay. Various pulse and square-wave techniques, eg, pulse voltammetry and square-wave voltammetry (10), are used to increase the rate of charging and therefore the precision, accuracy, and/or speed of the assay. 

Bond, A.M., Czerwinski, W.A. and Llorente, M. (1998) Comparison of direct current, derivative direct current, pulse and square wave voltammetry at single disc, assembly and composite carbon electrodes stripping voltammetry at thin film mercury microelectrodes with field-based instrumentation. Analyst, 123, 1333-1337. 

There are some simpler strategies that might do, and are easier to program. If an experiment such as double pulse or square wave voltammetry is simulated, the sharp changes occur at predictable times, and simple sequences of time intervals, such as exponentially expanding intervals, can be satisfactory, repeating the sequence at the onset of each pulse. 

Potentiodynamictechniques— are all those techniques in which a time-dependent -> potential is applied to an - electrode and the current response is measured. They form the largest and most important group of techniques used for fundamental electrochemical studies (see -> electrochemistry), -> corrosion studies, and in -> electroanalysis, -+ battery research, etc. See also the following special potentiodynamic techniques - AC voltammetry, - DC voltammetry, -> cyclic voltammetry, - linear scan voltammetry, -> polarography, -> pulse voltammetry, - reverse pulse voltammetry, -> differential pulse voltammetry, -> potentiodynamic electrochemical impedance spectroscopy, Jaradaic rectification voltammetry, - square-wave voltammetry. 

Separation of the cathodic and anodic components of the net current (measured at the end of forward and backward pulses) in square-wave voltammetries (SQWVs) provided only anodic components for PTA Y electrodes immersed into BU4NPI ),/ MeCN, as depicted in Figure 8.15. In contrast, SQWVs display well-developed anodic and cathodic components for PTA Y electrodes in contact with LiClO4/ MeCN. This feature, indicative of reversible electron transfer processes, was found to be more pronounced on decreasing square-wave frequency. 

Under optimized conditions, using differential pulse or square-wave voltammetries, linear peak current vs. dopamine concentration plots can be obtained in the 1-200 pM dopamine concentration range in the presence of 0.1 mM ascorbate, with detection limits (S/N= 3) of ca. 0.3 pM. 

The measurement of formal potentials allows the determination of the Gibbs free energy of amalgamation (cf Eq. 1.2.27), acidity constants (pATa values) (cf. Eq. 1.2.32), stability constants of complexes (cf. Eq. 1.2.34), solubility constants, and all other equilibrium constants, provided that there is a definite relationship between the activity of the reactants and the activity of the electrochemical active species, and provided that the electrochemical system is reversible. Today, the most frequently applied technique is cyclic voltammetry. The equations derived for the half-wave potentials in dc polarography can also be used when the mid-peak potentials derived from cyclic voltammograms are used instead. Provided that the mechanism of the electrode system is clear and the same as used for the derivation of the equations in dc polarography, and provided that the electfode kinetics is not fully different in differential pulse or square-wave voltammetry, the latter methods can also be used to measure the formal potentials. However, extreme care is advisable to first establish these prerequisites, as otherwise erroneous results will be obtained. 

Voltammetric techniques that can be applied in the stripping step are staircase, pulse, differential pulse, and square-wave voltammetry. Each of them has been described in detail in previous chapters. Their common characteristic is a bell-shaped form of the response caused by the definite amount of accumulated substance. Staircase voltammetry is provided by computer-controlled instruments as a substitution for the classical linear scan voltammetry [102]. Normal pulse stripping voltammetry is sometimes called reverse pulse voltammetry. Its favorable property is the re-plating of the electroactive substance in between the pulses [103]. Differential pulse voltammetry has the most rigorously discriminating capacitive current, whereas square-wave voltammetry is the fastest stripping technique. All four techniques are insensitive to fast and reversible surface reactions in which both the reactant and product are immobilized on the electrode surface [104,105]. In all techniques mentioned above, the maximum response, or the peak current, depends linearly on the surface, or volume, concentration of the accumulated substance. The factor of this linear proportionality is the amperometric constant of the voltammetric technique. It determines the sensitivity of the method. The lowest detectable concentration of the analyte depends on the smallest peak current that can be reliably measured and on the efficacy of accumulation. For instance, in linear scan voltammetry of the reversible surface reaction i ads + ne Pads, the peak current is [52]... 

Cyclic voltammetry Square-wave voltammetry Staircase voltammetry Linear-sweep voltammetry Fast cyclic voltammetry Rotating disc voltammetry Stripping voltammetry Hydrodynamic voltammetry Direct current (d.c.) polarography Alternating current (a.c.) polarography Pulse polarography... 

Notes Only a small fraction of a complete applied potential waveform scan is shown for differential pulse and square wave voltammetry. The entire measured signal for a single analyte is shown. 

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