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Reading Material ●Skoog, Holler and Crouch: Ch. 22 (An Introduction to Electroanalytical Chemisty) ●See also Skoog et al. Chapters 23-25. ●Cazes: Chapters 16-19 ●For those using electroanalytical chemistry in their work, the following reference is recommended: nd A. J. Bard and L. R. Faulkner, “Electrochemical Methods”, 2 Ed., Wiley, 2001. Advantages of Electroanalytical Methods Matched against a wide range of spectroscopic and chromatographic techniques, the techniques of electroanalytical chemistry find an important role for several reasons: – Electroanalytical methods are often specific for a particular oxidation state of an element – Electrochemical instrumentation is relatively inexpensive and can be miniaturized – Electroanalytical methods provide information about activities (rather than concentration) History of Electroanalytical Methods Michael Faraday: the law of electrolysis – “…the amount of a substance deposited from an electrolyte by the action of a current is proportional to the chemical equivalent weight of the substance.” Walter Nernst: the Nernst Michael Faraday Walter Nernst equation (Nobel Prize (1791-1867) (1864-1941) 1920) Jaroslav Heyrovsky: the invention of polarography: (Nobel Prize 1959) Jaroslav Heyrovsky (1890-1967) Main Branches of Electroanalytical Chemistry Interfacial Bulk methods methods Dynamic Conductometry Static methods methods (G = 1/R) (I = 0) (I > 0) Based on Figure 22-9 in Skoog, Holler and Potentiometry Crouch, 6th ed. (E) Controlled Constant potential current Voltammetry Amperometric Electro- Coulometric (I = f(E)) titrations gravimetry titrations (I = f(E)) (m) (Q = It) Key to measured quantity: I = current, E = potential, R = resistance, G = conductance, Q = quantity of charge, t = time, vol = volume of a standard solution, m = mass of an electrodispensed species Main Branches of Electroanalytical Chemistry Potentiometry: measure the potential of electrochemical cells without drawing substantial current – Examples: pH measurements, ion-selective electrodes, titrations (e.g. KF endpoint determination) Coulometry: measures the electricity required to drive an electrolytic oxidation/reduction to completion – Examples: titrations (KF titrant generation), “chloridometers” (AgCl) Voltammetry: measures current as a function of applied potential under conditions that keep a working electrode polarized – Examples: cyclic voltammetry, many biosensors
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