Solid microparticles, immobilized

F. Scholz, B. Meyer, Voltammetry of solid microparticles immobilized on electrode surfaces in Electroanalytical Chemistry, A Series of Advances (Eds. A. J. Bard, I. Rubinstein), Marcel Dekker, New York, 1998, p. 1, Vol. 20. 

Refs. [i] Scholz F, Nitschke L, Henrion G (1989) Naturwissenschaften 76 71 [ii] ScholzF, Meyer B (1998) Voltammetry of solid microparticles immobilized on electrode surfaces. In Bard A], Rubinstein I (eds) Elec-troanalytical chemistry, vol. 20. Marcel Dekker, New York [iii] Scholz F, Schroder U, GulaboskiR (2005) Electrochemistry of immobilized particles and droplets. Springer, Berlin... 

Voltammetry of Solid Microparticles Immobilized on Electrode Surfaces, Fritz Scholz and Birgit Meyer... 

Scholz F, Meyer B (1998) Voltammetry of solid microparticles immobilized on electrode surfaces. In Bard AJ, Rubinstein I (eds) Electroanalytical chemistry, a series of advances 20 1... 

In studies which focus on the redox properties of immobilized microparticles, electrode preparation and electrolyte composition are to be carefully considered. Almost any kind of solid electrode may be applied in order to investigate the redox properties of immobilized solid microparticles. However, attention must be drawn to possible catalytic properties of the electrode with respect to the reactions to be studied, and reactions of the electrolyte, which may or may not accompany the reactions of the solids. The surface hardness of the particular electrode should be kept in mind as well. For example, a hard electrode will allow soft or flake-like solids to be... 

Once solid microparticles of a compound have been immobilized on the surface of a suitable electrode, the electrochemical behavior can be studied. When a voltammetric method is used, the starting potential should be carefully set to a value where no reaction is expected. Alternatively, one may start at the open circuit potential, which either has been predetermined or which is measured by the instrument before commencing the scan. In principle, one can record the oxidation and the reduction response of the compound. In many cases it is useful to perform a pre-electrolysis of the compound, either a reduction or oxidation, followed by recording the response of the reverse processes. Thus metal sulfide or metal oxide particles can be converted to metal particles, which are oxidized in a follow-up scan to yield metal-specific signals, very much like in stripping voltammetry of solutions. Practically, there is no limitation with respect to electrochemical measurements that can be carried out with immobilized particles. 

The SWV of microparticles of the lipid-lowering drug simvastatin is shown in Fig. 3.8 [188]. The electrode reaction is totally irreversible, as indicated by the backward component of the response. The net peak potential is a linear function of the logarithm of SW frequency, as can be seen in Fig. 3.9. From the slope of this relationship (79 mV/d.u.) the product an = 0.75 was calculated [188]. These examples show that SWV can be used for the characterization of electrode reactions of microparticles immobilized on solid electrodes. 

Fig. 31 (A) Principle of a sandwich immunoassay using FDA particulate labels. The analyte is first immobilized by the capture antibody preadsorbed on the solid phase (a) and then exposed to antibody-coated microparticle labels (b). Every microparticle contains 108 FDA molecules. High signal amplification is achieved after solubilisation, release, and conversion of the precursor FDA into fluorescein molecules by the addition of DMSO and NaOH (c). (B) Calibration curves of IgG-FDA microcrystal labels with increasing surface coverage of detector antibody (a-d) compared with direct FITC-labeled detector antibody (e). The fluorescence signals increase with increasing IgG concentration. FDA microcrystals with a high IgG surface coverage (c,d) perform better than those with lower surface coverage (a,b). (Reprinted with permission from [189]. Copyright 2002 American Chemical Society)...

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Many electrochemical conversions of solid compounds and materials, including for example the corrosion of metals and alloys or the electrochemical conversions of most battery materials, take place within a liquid electrolyte environment, with the classic approach to investigation comprising macro-sized electrodes. However, in order to obtain a comprehensive understanding ofthe mechanism ofthese solid-state electrochemical reactions, the simple technique of immobilizing small amounts of a solid compound/material on an inert electrode surface provides an easy, yet sometimes exclusive, access to their study. In this chapter is presented a survey of the recent developments of this approach, which is referred to as the voltammetry of immobilized microparticles (VIM). Attention is also focused on progress in the field of theoretical descriptions of solid-state electrochemical reactions. 

The voltammetric behavior of surface-immobilized microparticles of redox active solid materials has been extensively studied by the groups of Scholz (Greifswald, Germany), Bond (Melbourne, Australia), Grygar (Rez, Czech Republic), Komorsky-Lovric and Lovric (Zagreb, Croatia), Domenech-Carbo (Valencia, Spain), Marken (Bath, UK), and others. Theoretical aspects, however, have been addressed only in some reports. Recently, the Compton group (Oxford, UK) made several reports on the theory of microparticle-modified electrodes, and these will mainly be discussed at this point. 

Metal oxide and hydroxide systems serve many functions, including roles as pigments, in mineralogy, and also in catalysis. The classic techniques used in such investigations have included diffraction (especially X-ray diffraction XRD), thermal analysis, transmission electron microscopy, Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy (see also Chapters 2 and 4). Until the introduction of voltammetry in the analysis of immobilized microparticles, electrochemical studies had been confined to solid electrolyte cells (Chapter 12), normally functioning at elevated temperatures. Unfortunately, these studies proved to be inapplicable for analytical characterization, and consequently a series of systematic studies was undertaken using immobilized microparticles of iron oxides and oxide-hydrates (for reviews, see... 

Kovanda et al. [67] have employed not only the voltammetry of immobilized microparticles but also several solid-state analytical techniques when studying the thermal behavior of a layered Ni-Mn double hydroxide. The important advantage of these electrochemical experiments was that they proved the presence of substantial amounts of amorphous compounds. Moreover, distinct signals could be identified for the reductive dissolution of the different phases. 

The organic and organometallic complexes of transition metals are especially important in catalysis and photovoltaics, on the basis of their redox and electron-mediating properties. Whilst most complex compounds can be studied in (organic) solution-phase experiments, their solid-state electrochemistry (often in an aqueous electrolyte solution environment) is in general also easily accessible by attaching microcrystalline samples to the surface of electrodes. Quite often, the voltammetric characteristics of a complex in the solid state will differ remarkably from its characteristics monitored in solution. Consequently, chemical, physical or mechanistic data are each accessible via the voltammetry of immobilized microparticles. 

Methods describing the electrochemical investigation of solid compounds and materials have significantly expanded to new possibilities over the last two decades. This chapter focuses on the use of a fairly new and straightforward method referred to as voltammetry of immobilized microparticles (VIM). Detailed reviews of the method are available elsewhere [la-c]. Beside applications in fundamental studies, this method proved to be especially valuable for the analysis of solid materials studied in archeometry [Id]. 

Figure II.8.3 gives two examples, one for the dependence of a voltammetric peak potential of copper reduction on the composition of copper sulfide-selenide solid solutions, and one for the dependence of the formal potentials (mid-peak potentials from cyclic voltammetry) of mixed iron-copper hexacyanoferrates on the composition of these compounds. The copper sulfide-selenides behave in very nonideal fashion, whereas the solid solution hexacyanoferrates give, within the limit of experimental errors, an almost linear dependence. These and other examples [18-21] are well suited to show that by voltammetric measurements of immobilized microparticles it is extremely facile to answer the two questions, is it a solid solution or not, and what is its composition.

Barbante GJ, Hogan CF, Hughes AB (2009) Solid state spectroelectrochemistry of microparticles of ruthenium diimine complexes immobilized on optically transparent electrodes. J Solid State Electrochem 13 599-608... 

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