Chrono potentiometry

These results are plausible since according to Sand a two-fold concentration of a component yields a four-fold transition time. Now, these features show, in contrast to the net separation and pure additivity of polarographic waves and their diffusion-limited currents as concentration functions, that in chrono-potentiometry the transition times of components in mixtures are considerably increased by the preceding transition times of any other more reactive component, which complicates considerably the concentration evaluation of chronopotentiograms. 

Within these broad categories two principal classes may be distinguished, depending on whether current or voltage is the controlled parameter. The individuals in each class are often described by an operational nomenclature consisting of an independent-variable part followed by a dependent-variable part (i.e., volt-ammetry, chrono-potentiometry) with some system-specific modifiers (i.e., rotating disk voltammetry). Unfortunately, the whims of history have left the electrochemical nomenclature in a rather confused state. The operational approach has been only partially adopted but seems to be gaining popularity. 

The product ix1/2 is a significant diagnostic parameter in chrono-potentiometry. It is apparent from the Sand equation that the quantity ixI/2 is a constant for a given concentration of electroactive species. The application of... 

The simulation of other electrochemical experiments will require different electrode boundary conditions. The simulation of potential-step Nernstian behavior will require that the ratio of reactant and product concentrations at the electrode surface be a fixed function of electrode potential. In the simulation of voltammetry, this ratio is no longer fixed it is a function of time. Chrono-potentiometry may be simulated by fixing the slope of the concentration profile in the vicinity of the electrode surface according to the magnitude of the constant current passed. These other techniques are discussed later a model for diffusion-limited semi-infinite linear diffusion is developed immediately. 

As indicated at the beginning of this chapter, the methodology of chrono-potentiometry is straightforward. Some care is necessary to ensure that the electrode configuration and placement are such as to cause the electrolysis to be limited by semiinfinite linear diifusion. Chapter 5 indicates a number of indicator-electrode designs that are appropriate for such performance. As in... 

For decades the electrochemical techniques, i.e., potential, current, or charge step methods such as - chronoamperometry, - chronocoulometry, - chrono-potentiometry, coulostatic techniques were consid-... 

Verfahren I Mikrocoulometrie. — II , Linear-sweep -Voltammetrie. — III Potentiostatische Verfahren. — IV Chrono-potentiometrie. — V Oscillopolarographie ((dEfdt — /( )). — VI Square-wave-Polarographie. 

Delahay P (1963) Chronoamperometry and chrono-potentiometry. In Kolthoff IM, Elving PJ and Sandell EB, eds. Treatise on analytical chemistry. Part I (Theory and practice), Vol 4, section D-2, Electrical methods of analysis (Reilley CN, section advisor), pp. 2233—2268. John Wiley Sons, New York. 

Table 2. Rate constants data for chronoamperometry and chrono potentiometry...

To study the actuation properties of Ni-doped MFR IPMCs, first the current and displacement in response to an applied voltage were measured in range from —3V to 3V. Due to the oxidation of Ni, the charging process starts at 0.8 V and electric breakdown takes place at 1.8 V. However, after the first cycle of operation, the cmrent density and the displacement remained rather imchanged (see Fig. 3.5). The actuation performance is shown in Fig. 3.6. The displacement of Ni-doped MFR IPMCs was mea-smed when a square pulse was applied using chrono-potentiometry with 2 s pulse dmation and controlled current. The results indicate that the actua-... 

In our previous investigation [1] we used equation (8) for determination of E c,(iiiycr(n)- For more precise calculation of values E cr(iiiycrai),coefficients of diffusion Cr(III), Cr(II) by methods of linear sweep voltammetry (LVA) and reversive chrono-potentiometry... 

M. St astny and P. Lepsi. Systematic and random error suppression in instrumentation for stripping (chrono) potentiometry. Review of Scientific Instruments 70 3439-3446,1999. 

For decades the electrochemical techniques, i.e., potential, current, or charge step methods such as chronoamperometry, -r chronocoulometry, chrono-potentiometry, coulostatic techniques were considered as fast techniques, and only with other pulse techniques such as temperature jump (T-jump) introduced by Eigen [i] or flash-photolysis method invented by Norrish and Porter [ii], much shorter time ranges became accessible. (For these achievements Eigen, Norrish, and Porter shared the 1964 Nobel Prize.) The advanced versions of flash-photolysis allow to study fast homogeneous reactions, even in the picosecond and femtosecond ranges [hi] (Zewail, A.H., Nobel Prize in Chemistry, 1999). Several other techniques have been elaborated for the study of rapid reactions, e.g., flow techniques (stopped-flow method), ultrasorhc methods, pressure jump, pH-jump, NMR methods. 

Both linear sweep voltammetry (oscillographic polarography, stationary electrode polarography, chronoamperometry with linear sweep) and chrono-potentiometry have been extensively applied for studies in molten salts. The advantages of linear sweep voltammetry include (1) extensively developed theory enabling the experimentalist to interpret the mechanisms of relatively complex electrode reactions (2) well-defined mass transfer conditions, particularly when faster scan rates ( 1 V/sec) are employed (3) the decrease of the faradaic charge with the square root of the scan rate and the resulting decrease of any modifications of the solid electrode caused by the faradaic process. Chronopotentiometry, 29) related electroanalytical... 

Scrosati determined the solubility of PdO in the melt by chrono-potentiometry. The results, which are in good agreement with those obtained by potentiometry, indicated that PdO is completely dissociated in the melt. The diffusion coefficient for Pd - was reported. Schmidt et studied the reduction of Bi +, Pd +, Pt +, and Sb - voltammetrically with an inter-mittenly polarized platinum electrode. The shape of the current-voltage curves for Pd + and Pt was described by the Kolthoff-Lingane equation, whereas for Bi + and Sb + the Heyrovsky-Ilkovic equation was valid. The diffusion coefficients for the species were reported. 

Sakakura studied the electrodeposition of zirconium by chrono-potentiometry. A well-defined one-step chronopotentiogram corresponding to Zr + + 2e Zr was obtained for ZrClg. No interpretation of the chrono-potentiograms of ZrCl4 was attempted. The diffusion coefficients for Zr - " and Zr + were reported. 

The early methods for assessment of such metal fractions had employed mainly voltammetric techniques, later supplemented or also altered by stripping (chrono)potentiometry. " " The corresponding procedures were designed as more or less uniform schemes combiuing the identification and determination of... 

Van Leeuwen HP, Town RM (2003) Electrochemical metal speciation analysis of chemically heterogeneous samples the outstanding featirres of stripping chrono-potentiometry at scatmed deposition potential. Environ Sci Technol 37 3945—3952... 

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