Auxiliary electrodes function

An additional electrolyte can also provide the auxiliary electrode function. For example, Na2CO3 can be used with NaP alumina [135-137], NASICON [138-146], or a sodium aluminosilicate glass [147] as the electrolyte for a CO2 sensor, in which case the Na2CO3 equilibrates with CO2 in the gas and Na in the electrolyte according to the following reaction ... 

Electrochemical measurements usually concern not a galvanic cell as a whole but one of the electrodes, the working electrode (WE). However, a complete cell including at least one other electrode is needed to measure the WE potential or allow current to flow. In the simplest case a two-electrode cell (Eig.l2.1a) is used for electrochemical studies. The second electrode is used either as the reference electrode (RE) or as an auxiliary electrode (AE) to allow current to flow. In some cases these two functions can be combined for example, when the surface area of the auxiliary electrode is much larger than that of the working electrode so that the current densities at the AE are low, it is essentially not polarized and thus can be used as RE. 

The Hewlett-Packard HP 1049A Electrochemical Detector cellbody (see Figure 3-9) functions as the auxiliary electrode thereby shielding cell inlet, outlet and reference electrode effectively against indirect influence of electric field changes via the liquid lines. 

Figure 6.18b depicts the classical three-electrode constant-current experiment. The counter electrode is now replaced by an auxiliary electrode and a reference electrode. The reference electrode enables one to monitor the working electrode potential as a function of time using a high-impedance (zero-cur-rent) measuring device. In many early experiments, carried out on a time scale... 

An electrochemical detector is destructive. It requires (1) a working electrode (where oxidation or reduction takes place), (2) an auxiliary electrode, and (3) a reference electrode (to regulate voltage and compensate for changes in background conductivity of the eluent). When an active substance flows into the electrochemical cell and a potential difference is applied between the working and reference electrodes, the electrolysis of the analyte yields a current (detector signal) that is a function of the applied potential. The three steps in the process are ... 

Figure 11.25. The polarization curve. The corroding iron is used as an electrode, a variable voltage is applied (against an auxiliary electrode), and the current density is measured as cl function of the electrode potential. The measured current density is composed of the cathodic and anodic current density, i, = At the open circuit,...

Electrochemical sensor potentials with lithium-ion conducting electrolytes and Li2C03-BaC03 auxiliary electrodes at 500°C as a function of the carbon dioxide concentration (Fergus, 2008). Numbers [24], [25], [27] and [30] refer to the following references 24, Park et at. (2003) 25, Noh etal. (2005) 27, Menil etal. (2005) 30, Satyanarayana etal. (2007). 

Optimisation of an HPLC system for a specific analysis can be a complex task and many additional factors must be considered when using EC detection. These can be divided into system dependent variables and analyte dependent variables. System dependent variables include the nature of the working, reference and auxiliary electrodes and associated electronics, and the applied potential as discussed in Chapters 2 and 3. In addition, there may be influences from the eluent (solvent composition, pH, ionic strength), temperature and flow-rate. Analyte-dependent variables are specifically the presence of one or more electroactive moieties or functional groups on the compound(s) of interest. With compounds which are not inherently electroactive it may be possible to derivatise them, or to chemically modify them in some other way, to impart electrochemical properties. 

A voltammetric measurement is accomplished by scanning the potential difference across an electrochemical cell containing a working electrode. a reference electrode and usually an auxiliary electrode separated from the sample solution with a diaphragma from one preset value to another and recording the cell current as a function of the applied potential. A curve so generated is known as a voltammogram. Amperometric meas-... 

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