Electrochemical noise statistical analysis

Analysis methods for electrochemical noise data can be separated into three categories, (1) deterministic, (2) statistical, and (3) spectral. Deterministic methods involve the use of mixed potential theory to explain the oscillations that occur. For example, if the ZRA current increases suddenly while the potential difference between the two current electrodes and the potential electrode increases, localized corrosion has likely initiated on one of the current electrodes. A common pitfall in such a measurement is that if a nominally identical reference electrode is used, it could pit as well, leading to no change in potential versus the coupled electrodes. Due to the need for careful interpretation, deterministic methods are not widely used. 

The theoretical treatment of electrochemical noise is not complete. There does not yet seem to be consensus on which signal analysis techniques are most useful. It is fairly clear, however, that understanding of ENM requires a good working knowledge of statistics anyone setting out to master the technique must steel themselves to hear of kurtosis, skewness, and block averages rather frequently. 

The quantitation of enzymes and substrates has long been of critical importance in clinical chemistry, since metabolic levels of a variety of species are known to be associated with certain disease states. Enzymatic methods may be used in complex matrices, such as serum or urine, due to the high selectivity of enzymes for their natural substrates. Because of this selectivity, enzymatic assays are also used in chemical and biochemical research. This chapter considers quantitative experimental methods, the biochemical species that is being measured, how the measurement is made, and how experimental data relate to concentration. This chapter assumes familiarity with the principles of spectroscopic (absorbance, fluorescence, chemi-and bioluminescence, nephelometry, and turbidimetry), electrochemical (poten-tiometry and amperometry), calorimetry, and radiochemical methods. For an excellent coverage of these topics, the student is referred to Daniel C. Harris, Quantitative Chemical Analysis (6th ed.). In addition, statistical terms and methods, such as detection limit, signal-to-noise ratio (S/N), sensitivity, relative standard deviation (RSD), and linear regression are assumed familiar Chapter 16 in this volume discusses statistical parameters. 

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