Electrochemical methods applications

The electrical parameters that are measured are current and voltage (amperometric, potentiometric or voltammetric), impedance, and conductivity. In this section, we discuss electrochemical methods applicable to LOC devices. 

Bard A J and Falkner L R 1980 Electrochemical Methods—Fundamentals and Applications (New York Wiley)... 

The majority of FI A applications are modifications of conventional titrimetric, spectrophotometric, and electrochemical methods of analysis. For this reason it is appropriate to evaluate FIA in relation to these conventional methods. The scale of operations for FIA allows for the routine analysis of minor and trace analytes and for macro-, meso-, and microsamples. The ability to work with microliter injection volumes is useful when the sample is scarce. Conventional methods of analysis, however, may allow the determination of smaller concentrations of analyte. 

Cathodic Protection This electrochemical method of corrosion control has found wide application in the protection of carbon steel underground structures such as pipe lines and tanks from external soil corrosion. It is also widely used in water systems to protect ship hulls, offshore structures, and water-storage tanks. 

Anodic Protection This electrochemical method relies on an external potential control system (potentiostat) to maintain the metal or alloy in a noncorroding (passive) condition. Practical applications include acid coolers in sulfuric acid plants and storage tanks for sulfuric acid. 

The reduction of dimensions also reduces volumes which are accessible to the detector. Thus, detection principles related to geometric dimensions of the detector cell ai e not ideally suited for coupling to microsystems, whereas surface sensitive principles, such as electrochemical methods or optical methods utilizing the evanescent field of a waveguide, or methods which can be focussed on a small amount of liquid, such as electrochemiluminescence (ECE), ai e better suited. This is why electrochemiluminescence detectors ai e combined to microsystems. Moreover ECE has found wide applications in biochemistry because of its high sensitivity, relatively simplicity and feasibility under mild conditions. 

The measurement of transport numbers by the above electrochemical methods entails a significant amount of experimental effort to generate high-quality data. In addition, the methods do not appear applicable to many of the newer non-haloalu-minate ionic liquid systems. An interesting alternative to the above method utilizes the NMR-generated self-diffusion coefficient data discussed above. If both the cation (Dr+) and anion (Dx ) self-diffusion coefficients are measured, then both the cation (tR+) and anion (tx ) transport numbers can be determined by using the following Equations (3.6-6) and (3.6-7) [41, 44] ... 

A. J. Bard and L.R. Faulkner, Electrochemical Methods Fundamentals and Applications , 2" edition, John Wiley Sons, Inc., 2001, ISBN 0-471-04372-9. S. Takahashi, K. Akimoto, I. Saeki, Hyomen Gijutsu 1989, 40, 134. 

A detailed and well-referenced account of electrochemical methods of testing has been written by Dean, France and Ketcham in a section of the book by Ailor. ASTM G5 1987 outlines standard methods for making potentiostatic and potentiodynamic anodic polarisation measurements and ASTM G3 1974 (R1981) gives conventions applicable to electrochemical measurements in corrosion testing. 

A J Bard and L R Faulkner Electrochemical Methods Fundamentals and Applications, J. Wiley and Sons, New York, 1980... 

Pleischmann and Fletcher, 1969, 1971 Lund, 1967 Mann and Barnes, 1970 Peover, 1967, 1971 Wawzonek, 1967 Weinberg and Weinberg, 1968) and in spite of the fact that reactive intermediates may readily be produced from inert starting materials, electrochemical methods have still not found general application. 

Bard, AJ, and Faulkner, LR (1980), Electrochemical, Method, Fundamental and Application, Wiley, New York, p 142. 

The Volta potential is defined as the difference between the electrostatic outer potentials of two condensed phases in equilibrium. The measurement of this and related quantities is performed using a system of voltaic cells. This technique, which in some applications is called the surface potential method, is one of the oldest but still frequently used experimental methods for studying phenomena at electrified solid and hquid surfaces and interfaces. The difficulty with the method, which in fact is common to most electrochemical methods, is lack of molecular specificity. However, combined with modem surface-sensitive methods such as spectroscopy, it can provide important physicochemical information. Even without such complementary molecular information, the voltaic cell method is still the source of much basic electrochemical data. 

Bard, A., and L. Faulkner, Electrochemical Methods Fundamentals and Applications, Wiley, New York, 2001. 

Electrochemical methods of protection rest on different precepts (1) electroplating of the corroding metal with a thin protective layer of a more corrosion-resistant metal, (2) electrochemical oxidation of the surface or application of other types of surface layer, (3) control of polarization characteristics of the corroding metal (the position and shape of its polarization curves), and (4) control of potential of the corroding metal. 

It is the purpose here to briefly review the state of the art of the most important electrochemical methods for medical applications, and report on the status and viability of currently emerging research. To accomplish this, electrochemical methods have been divided into four basic categories. The first two categories (Sect. 2 and 3) represent the relatively mature contribution of electrochemistry to medical diagnostics. Sections four and five deal largely with developments in electrochemistry which have not yet achieved commercialization, but which have the greatest likelihood of future success. There are, of course, some minor areas of research which have been intentionally omitted because of space limitations. Much of this work can be found in the references provided in the text. 

Other important alternate electrochemical methods under study for pCO rely on measuring current associated with the direct reduction of CO. The electrochemistry of COj in both aqueous and non-aqueous media has been documented for some time 27-29) interferences from more easily reduced species such as O2 as well as many commonly used inhalation anesthetics have made the direct amperometric approach difficult to implement. One recently described attempt to circumvent some of these interference problems employs a two cathode configuration in which one electrode is used to scrub the sample of O by exhaustive reduction prior to COj amperometry at the second electrode. The response time and sensitivity of the approach may prove to be adequate for blood ps applications, but the issue of interfering anesthetics must be addressed more thorou ly in order to make the technique a truly viable alternative to the presently used indirect potentiometric electrode. 

Electroorganic Synthesis by Indirect Electrochemical Methods New Applications of Electrochemical Techniques ... 

Application of electrochemical methods as analytical tools for the detection as well as the concentration and activity determination of biologically active compounds in bioanalysis and medicine ... 

Bard, A. J. Faulkner, L. R. Electrochemical Methods, Fundamentals and Applications Wiley, New York, 1980. 

Only few applications have been reported to determine antioxidants in rubbers or polymers by using electrochemical methods [927,928]. Sawada et al. [929] reported successful separations by coupling the antioxidants with p-diazobenzene sulfonic acid before electrophoresis. Amine AOs were coupled in acetic acid and phenolic AOs in NaOH-ethanol were analysed by CE methods. MEKC separation of the four major food grade antioxidants (PG, BHA, BHT, TBHQ) was completed within 6 min with pmole amount detection using UV absorption [930]. RPLC was not as efficient and required larger sample amounts and longer separation times. 

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