Different methods of graphite electrode treatment and their effect on the electrochemical behavior of a small adsorbing biological molecule, 2,6-diamino-8-purinol

Abstract

30) ooeddel, D. V.; Heyneker, H. L.; Hozuml, T.; Arentzen, R.; Itakura. K.; Yansura. D. 0.; Ross, M. J.; Miozzari, G.; Crea, R.; Seeburg, P. H.Effect of the method of electrode treatment and the electrode material on the behavlor of the adsorbing small blologlcal molecule 2,6-dlamino-8-purinoi was evaluated. Electrochem lcal oxldatlon, polishlng, and laser activation were the methods of treatment that were compared and glassy carbon and rough pyrolytic graphite were the electrode materials. The results Indicate that effects such as chemlstry of the surface rather than microscopic surface area may determlne the b e havior of this adsorbing molecule.The chemistry and structure of graphite surfaces play a key role in heterogeneous electron transfer (I). Active surfaces, Le., surfaces at which kinetics of electron transfer are effec-tively catalyzed, can be produced by different methods. Improved electrochemical behavior is observed for compounds and at surfaces that are very different. This indicates that different mechanisms may be responsible for the effective catalysis (2). It has been suggested that a decrease in hydrophobicity of activated surfaces (2) may be the major factor in the observed catalytic behavior. It has also been proposed that activation follows desorption of impurities from the electrode surface (3, 4 ) .As a result of activation of glassy carbon electrodes by electrochemical treatment (5,6), polishing with alumina (3) and laser activation (4), background capacitance can increase. Increase in background capacitance has been related to an increase in adsorption (7). For example, when alumina-polished and heat-treated glassy carbon electrodes were com-

Electrochemical and XPS Characterization of Glassy Carbon Electrode Surface Effects on the Preparation of a Monomeric Molybdate(VI)-Modified Electrode

“…The surface excess of Mo(VI) ion, τ i , versus Q GC is reported in Figure , which indicates a gradual decrease in τ i with an increase in Q GC . This is strikingly in contrast to other systems investigated so far on GCE for their adsorption behavior, namely, catechol, ruthenium(III) and cobalt(III) hexamines, dopamine, nitrobenzene, 1,2,4-trihydroxybenzene, ruthenium bipyridine, and 2,6-diaminopurinol, all of which have shown enhanced adsorption with an increase in surface charge on GCE introduced by electrochemical oxidation pretreatment. It has been reported that an increase in adsorption is accompanied by an increase in the background current and an increase in the apparent electron-transfer rate. , These increases have been associated with the creation of active sites. , It must be mentioned here that all the previous studies on the question of GCE activation have shown that the oxidized surface alone facilitates adsorption and electron-transfer rates. ,,− The method of cathodic pretreatment has not been reported to activate the carbon electrodes toward any redox system except isopolymolybdic acid, but the origin for the enhanced activation remains unknown.…”

“…This is strikingly in contrast to other systems investigated so far on GCE for their adsorption behavior, namely, catechol, ruthenium(III) and cobalt(III) hexamines, dopamine, nitrobenzene, 1,2,4-trihydroxybenzene, ruthenium bipyridine, and 2,6-diaminopurinol, all of which have shown enhanced adsorption with an increase in surface charge on GCE introduced by electrochemical oxidation pretreatment. It has been reported that an increase in adsorption is accompanied by an increase in the background current and an increase in the apparent electron-transfer rate. , These increases have been associated with the creation of active sites. , It must be mentioned here that all the previous studies on the question of GCE activation have shown that the oxidized surface alone facilitates adsorption and electron-transfer rates. ,,− The method of cathodic pretreatment has not been reported to activate the carbon electrodes toward any redox system except isopolymolybdic acid, but the origin for the enhanced activation remains unknown. The immediate conclusion that is obvious from the results of Figure is that there is strong specific interaction between Mo(VI) and the functional groups on the GC surface introduced by cathodic treatment; this kind of favorable interaction is totally absent on anodized surface.

5 Dependence of adsorbed Mo(VI) surface excess on pretreated GC electrode surface charge ( Q GC ): peak C1 (○); peak C2 (▵); peak C3 (□).

…”

“…Studies have been carried out with polished GCE for comparison. The results show that monomeric molybdate(VI) adsorption is remarkably higher on the electrochemically reduced GCE surface, but there is no adsorption on the anodically pretreated electrode, unlike the other redox systems studied until now, ,,,,− which showed enhanced adsorption on electrochemically oxidized carbon electrodes.…”

“…To obtain a stable monomeric molybdate(VI) coating on GCE, the surface pretreatment method of GCE has to be formulated in the first place. Several pretreatment procedures specific for specific electrochemical reactions in solution − and adsorption and electron-transfer processes of adsorbable substrates ,,− have been proposed. These include electrochemical methods, − nonelectrochemical methods such as polishing, − vacuum heat treatment, ,,, laser irradiation, − fracturing, − and high-intensity ultrasonic treatment …”

Electrochemical impedance study and sensitive voltammetric determination of Pb(ii) at electrochemically activated glassy carbon electrodes

“…15 Various pretreatment (or activation) procedures, depending on the kind of analysis and nature of the redox system, have been adopted to achieve faster electron transfer rates and more reproducible results. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In the case of electrochemical activation, preanodization at very positive potentials has been accepted as the prime activating procedure, although other pretreatments, such as preanodization followed by short-time cathodization 16,[18][19][20][21] and exclusive precathodization, 27,28 have also been reported. Such pretreatments are believed to result in an increase of surface quinone and other functional groups, which can then catalyse the oxidation/ reduction of the analyte.…”