Sono-Voltammetry

A solution of 0.5 mM ferrocene (Fc) in acetonitrile was studied at a platinum electrode of diameter 3 mm in the presence and absence of ultrasound. The ultrasound was provided by a sonic horn positioned opposite to the electrode, which could provide power of up to 60 W cm .  

Under silent conditions, a peak-shaped voltammogram was obtained, whereas under sonication very much larger currents flowed and the voltammogram became sigmoidal and steady state in character, with some spiking seen on the limiting current plateau. 

Comment on this, and estimate the approximate diffusion layer thickness under insonation if a limiting current of 314/tA was observed in the sono-voltammogram. The diffusion coefficient of ferrocene in acetonitrile is 2.3 x 

In quiescent solution, a familiar peak-shaped voltammogram is seen as expected for a macro electrode under planar diffusion-only transport. In contrast, inso nation establishes a strong convective flow as a result of acoustic streaming such that mass transport to the electrode is enhanced significantly. Under the latter conditions, applying the simple Nernst diffusion layer model gives an expression for the limiting current  

This value is very small compared to the diffusion layer seen at macroelectrodes under silent conditions. 

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The properties and applications of microelectrodes, as well as the broad field of electroanalysis, have been the subject of a number of reviews. Unwin reviewed the use of dynamic electrochemical methods to probe interfacial processes for a wide variety of techniques and applications including various flow-channel methods and scanning electrochemical microscopy (SEM), including issues relating to mass transport (1). Williams and Macpherson reviewed hydrodynamic modulation methods and their mass transport issues (2). Eklund et al. reviewed cyclic voltammetry, hydrodynamic voltammetry, and sono-voltammetry for assessment of electrode reaction kinetics and mechanisms with discussion of mass transport modelling issues (3). Here, we focus on applications ranging from measnrements in small volumes to electroanalysis in electrolyte free media that exploit the uniqne properties of microelectrodes. 

Ekiund J C, Markem F, Waller D N and Compton R G 1996 Voltammetry in the presence of ultrasound, a novel sono-electrode geometry E/eofrooh/m. Aofa 41 1541... 

Eklund JC, Marken F, Waller DN et al (1996) Voltammetry in the presence of ultrasound a novel sono-electrode geometry. Electrochim Acta 41 1541-1547... 

Hardcastle JL, Compton RG (2001) The electroanalytical detection and determination of copper in heavily passivating media ultrasonically enhanced solvent extraction by N-benzoyl-N-phenyl-hydroxylamine in ethyl acetate coupled with electrochemical detection by sono-square wave stripping voltammetry analysis. Analyst 126 2025-2031... 

Associated with electrode damage, the cleaning or depassivation of electrode surfaces is an important aspect of sono-electrochemistry. This effect has heen documented for the depassivation of iron electrodes [35), the removal of deposits [45), and observed when polymer films are present at the electrode surface [46). It is also vital to sonoelectroanalytical methods (see Sect. 2.8.1.2). The oxidation of the carbonyl complex Cr(CO)6 is an example of an electrochemical system that is prone to electrode passivahon [42). In the presence of ultrasound, sustained voltammetric currents can be obtained, which suggested both depassivation and/or a suppression of precipitation this is in contrast with corresponding silent voltammetry in which these phenomena preclude clean voltammetry. 

Applications of Sono-adsorptive Stripping Voltammetry (Sono-AdSV)... 

Applications of Sono-cathodic Stripping Voltammetry (Sono-CSV)... 

Saterlay et al, investigated ultrasonicallyassisted cathodic stripping voltammetry (CSV) at a boron doped diamond electrode, for the detection of lead. [46]. Square wave sono CSV was employed to obtain a response for Pb2+ in river sediment. Additions of an aqueous lead standard were then performed. Extrapolation of the stripping currents resulting from the lead additionsr facilitated the quantification of lead in the acid digest, and hence a lead content of 187.1 mg/kg was calculated for the sediment sample. 

The limit of detection by square-wave voltammetry after a 20-s deposition time was found to be 0.1 mM and 1.0 mM with and without microwave activation, respectively. The Pb content in a water sediment sample detected by anodic stripping voltammetry at boron doped diamond electrodes is shown to be in good agreement with two other independent analytical procedures based on ICP mass spectroscopy and on sono-cathodic stripping voltammetry. 

Banks CE, Rees NV, Compton RG (2002) Sonoelectrochemistry understood via nanosecond voltammetry sono-emulsions and the measurement of the potential of zero charge of a solid electrode. J Phys Chem B 106 5810-5813... 

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