Potentiometric analysis constant current

Thus, classical electrochemical stripping analysis (ESA) had spawned an offspring—adsorptive stripping voltammetry (AdSV) that became soon one of the most frequent techniques in electrochemical trace determination of metals (see, e.g., reference (113) and references therein). The determinations by AdSV and the related potentiometric method, constant current (adsorptive) stripping analysis, CCSA, are characterised by high selectivity which can be yet improved in the open-circuit arrangement and/or medium exchange.AdSV also offers remarkable detection capabilities down to the nanomolar level (see Table 5.2 and references (94, 97, 108, 110)). 

Huang HE, Jagner D, Renman L (1988) Flow potentiometric and constant-current stripping analysis for silver(I) with carbon-fiber and platinum-fiber electrodes. Anal Chun Acta 207 27-35... 

Scale of Operation Coulometric methods of analysis can be used to analyze small absolute amounts of analyte. In controlled-current coulometry, for example, the moles of analyte consumed during an exhaustive electrolysis is given by equation 11.32. An electrolysis carried out with a constant current of 100 pA for 100 s, therefore, consumes only 1 X 10 mol of analyte if = 1. For an analyte with a molecular weight of 100 g/mol, 1 X 10 mol corresponds to only 10 pg. The concentration of analyte in the electrochemical cell, however, must be sufficient to allow an accurate determination of the end point. When using visual end points, coulometric titrations require solution concentrations greater than 10 M and, as with conventional titrations, are limited to major and minor analytes. A coulometric titration to a preset potentiometric end point is feasible even with solution concentrations of 10 M, making possible the analysis of trace analytes. 

Two distinctly different coulometric techniques are available (1) coulometric analysis with controlled potential of the working electrode, and (2) coulometric analysis with constant current. In the former method the substance being determined reacts with 100 per cent current efficiency at a working electrode, the potential of which is controlled. The completion of the reaction is indicated by the current decreasing to practically zero, and the quantity of the substance reacted is obtained from the reading of a coulometer in series with the cell or by means of a current-time integrating device. In method (2) a solution of the substance to be determined is electrolysed with constant current until the reaction is completed (as detected by a visual indicator in the solution or by amperometric, potentiometric, or spectrophotometric methods) and the circuit is then opened. The total quantity of electricity passed is derived from the product current (amperes) x time (seconds) the present practice is to include an electronic integrator in the circuit. 

Tip/MWCNT/AuSPE Trp Constant current potentiometric stripping analysis and EIS 4.9xl0 mol per L/1.0xl0- -1.0xl0-4mol per L Majidi et al. (2016)... 

Figure 2.36. Experimental set-up for constant-current stripping analysis (also chronopoten-tiometric stripping or potentiometric stripping analysis (PSA))...

New instrumental techniques have been developed simultaneously with new applications to make possible more rapid and convenient methods of analysis. A commercial constant-current source covering a current range of 4.82 to 193.0 ma is used in conjunction with an automatic potentiometric end-point detection device designed specifically for this purpose. It does not require a predetermined end-point potential and requires only two preliminary adjustments prior to titration. A re-... 

Amperometry is a voltammetric method in which a constant potential is applied to the electrode and the resulting current is measured. Amperometry is most often used in the construction of chemical sensors that, as with potentiometric sensors, are used for the quantitative analysis of single analytes. One important example, for instance, is the Clark O2 electrode, which responds to the concentration of dissolved O2 in solutions such as blood and water. 

Reference to Table 4.1 indicates that olefins can be determined by the electrochemical generation in situ of halogens. Bromine is effective for both olefins and sulfur compounds and is the basis for an automatic coulometric titrator for continuous analysis of petroleum streams.17 The basic principle of this instrument is a potentiometric sensing system that monitors bromine concentration in a continuously introduced sample stream. The bromine in the solution reacts with the sample components and causes a decrease in the concentration of bromine. When this decrease is sensed by the potentiometric detection electrodes, the electrolysis current producing bromine adjusts itself to maintain the bromine concentration. Because the sample is introduced at a constant rate, the electrolysis current becomes directly proportional to the concentration of the sample component. Thus, the instrument records the electrolysis current as concentration of sample component and provides a continuous monitor for olefins or sulfur in petroleum streams. 

Three broad classifications of electrochemical methods are used in this chapter. Po-tentiometric methods include zero-current potentiometry and methods in which current of controlled magnitude is apphed to the working electrode, such as in potentiometric stripping analysis (PSA). Amperometric methods consider all techniques in which current is measured these include constant-potential amper-ometry and amperometric measurements made in response to a variety of applied potential waveforms in voltammetric methods. Impedimetric methods comprise a final classification in these methods, faradaic currents are generally absent, and impedance, conductance, or capacitance is the measured property. 

Potentiometric stripping analysis is carried out in several stages. After electrochemical generation of the mercury film on a graphite substrate, the elements to be determined are accumulated by electrolysis at constant potential. The next stage is the oxidation of the deposited elements by the oxidant present in the. solution. For this, the current circuit is disconnected. The deposited analytes are stripped in the order of their electrochemical jxitentials. Anodically deposited precipitates can similarly be stripped by chemical reduction. In all cases, potential - time curves with transition times proportional to concentration result [39]-[41]. 

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