Monitoring methods Electrochemical

Electrochemical On-Line Corrosion Monitoring On-line corrosion monitoring is used to evaluate the status of equipment and piping in chemical process industries (CPI) plants. These monitoring methods are based on electrochemical techniques. To use on-line monitoring effectively, the engineer needs to understand the underlying electrochemical test methods to be employed. This section covers many of these test methods and their applications as well as a review of potential problems encountered with such test instruments and how to overcome or avoid these difficulties. 

The enzyme immobilisation was carried out on 7,7,8,8-tetra-cyanoquinodimethane (TCNQ)-modified screen-printed electrodes. TCNQ allows the electrochemical oxidation of thiocholine, the product of the reaction between acetylthiocholine and the enzyme, at +100 mV (vs. Ag/AgCl) (Fig. 16.6). The enzymatic activity of the acetylcholinesterase can thus be monitored by electrochemical methods. 

Kurzweil P, Fischle HJ. A new monitoring method for electrochemical aggregates by impedance spectroscopy. Journal of Power Sources 2004 127 331-340. 

Andreescu, S. Sadik, O. A., Advanced electrochemical sensors for cell cancer monitoring, Methods 2005, 37, 84-93... 

Figure 1.1 Typical experimental setup used for the combined application of micro-optical and electrochemical methods along with in situ microscopic sample monitoring. The electrochemical cell is mounted on an x,y,z-stage and can be scanned with submicron resolution. Besides the nl-photoresistdroplet, the contact cell shown can also be used [39].

S. Hamyama and T. Tsum, A Corrosion Monitor Based on Impedance Method, Electrochemical Corrosion Testing, STP 727, F. Mansfeld and U. Bertocci, Ed., ASTM, 1981, p 167-186... 

For pesticide analysis, the potential of enzyme biosensors has been tested. In this field, biosensors based on the inhibition of acetylcholinesterases, acylcholinesterases, or butylrylchol-inesterases by organophosphorus compounds are widely used. Their specific activity can be monitored by electrochemical methods such as the ion-selective electrode and the ion-selective field effect transistor (ISFET). 

Electrochemical monitoring methods have also been developed for application on steel reinforcement in concrete. These methods include potential measurement on the concrete surface, linear polarization (LPR) and determination of polarization curves [9.17]. Electrical resistance probes (ER) and probes embedded in the concrete for measuring galvanic current have also been used. 

A number of experimental electrochemical methods are available. These include voltammetry under transient conditions (e.g. cyclic voltammetry) or under steady state conditions (e.g. rotating disk electrode), and spectroelectrochemistry (e.g. using UV-Vis spectroscopy to monitor an electrochemical process). We focus here on cyclic voltammetry. It is a readily available technique and information that can be gained includes ... 

Kihira et al. [118] applied EIS to investigate the condition of the rust film formed on the weathering steel, and proposed new corrosion monitoring method based on rust film resistance. Nishimura et al. [119] measured the electrochemical impedance of a carbon steel covered with rust film formed in a wet/dry environment containing chloride ions. They reported that the charge transfer resistance (/ p) increased with the wet-dry cycles of exposure. 

All above mentioned criteria are fulfilled by electrochemical methods. Electrochemical methods are attractive for ecological research also because they enable immediate measurement of changes in the component concentrations and because they can be frequently used for continuous monitoring and are suitable for field work, where the systematic error caused by transport and storage of the sample is avoided. It is true that there are a number of much more sensitive physical methods (X-ray electron difraction, neutron activation analysis, mass spectrometry, etc.) which, however, cannot be used in the field and are very expensive. 

MWCNT electrodes have been developed to monitor the electrochemical oxidation of insulin, a pancreas-produced hormone that plays a key role in the regulation of carbohydrates and fat metabolism in the body. This provides a possible method to evaluate the quality of pancreatic islets before their transplantation. By coating similar MWCNT electrodes with platinum microparticles, thiols containing amino acids can be detected in rat striatal that is the subcortical part of the fore-brain. CNT-based sensors can be incorporated into flexible biocompatible substrates to facilitate in vivo sensing. For instance, free cholesterol in blood can be measured using MWCNT electrodes placed on a biocompatible substrate whereas flexible pH sensors can be formed from polyaniline (a conductive polymer) and nanotube composites. ... 

HPLC elutes can also be monitored by electrochemical (EC) means, and HPLC-EC systems have been described for the measurement of vitamin D in a number of situations. While this is an interesting and potentially valuable means of measuring vitamin D metabolites, and it does appear that at the moment these procedures are sufficiently sensitive for the measurement of plasma or serum concentrations, there is only one published method applied to plasma analysis. Table 6 gives a list of such methods which have been published in the last 10 years. 

Electrochemical monitoring methods involve the determination of specific interface properties divided into three broad categories ... 

Haruyama S, Tsuru TA. Corrosion monitor based on impedance method electrochemical corrosion testing. In Mansfeld F, Bertocci U. eds. Computer Modeling in Corrosion [STP 727], Philadelphia, Pa. American Society for Testing and Materials. 1981 167-186. 

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