Search

A highly sensitive electrode for sensing glucose has been fabricated by electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole on a solid carbon paste substrate, and subsequent electrodeposition of multi-layer stacked copper particles as an outer surface. The individual copper particles are characterized by a large number of edges and corners of crystallites. Their preferred orientation {111} is parallel to the electrode surface. The conductive polymer interlayer results in an increase of the particle nucleation density and a further decrease of the polarization overpotential for direct (enzyme-free) oxidation of glucose in 0.1 M NaOH solution. A well-shaped voltammetric peak can be observed at around 0.3-0.5 V (vs. SCE, depending on scan rate) that is due to glucose oxidation. This potential is much lower than the one required for Cu(III) formation. A bulk electrolysis experiment using a thin-layer electrochemical cell confirmed the assumption that that glucose undergoes 2-electron oxidation. The mechanism of glucose oxidation in the absence of Cu(III) is discussed. The electrode exhibits a very high sensitivity (slope) of 3.31 mA cm mM, and the detection limit is 2 μM (at an SNR of 3). Features of the new sensor include the ease of fabrication, its high stability and good selectivity. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] Phytate greatly inhibits corrosion of brass in NaOH. [•] Eight cyclic voltabsorptometry peaks correspond to reactions of various ions. [•] Phytate can suppress formation of various zinc and cupric ions. [•] A spectroelectrochemical cell allows its light path length to be changed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new coupling of thin-layer electrolysis with capillary electrophoresis (CE). [•] Rapid electrolysis, direct sampling followed by online CE separation. [•] At least 13 products of quercetin oxidation were separated. [•] Thermodynamic and kinetic parameters were determined from CE peak areas. [ABSTRACT FROM AUTHOR]

Abstract: Raloxifene is a selective estrogen receptor modulator that may produce toxic oxidative species in metabolism. The oxidation mechanism of raloxifene with different pH values was studied by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), in situ UV–vis spectral analysis and cyclic voltabsorptometry based on a long optical-path thin-layer electrochemical cell. Time-derivative cyclic voltabsorptograms were obtained for comparative discussion with the corresponding cyclic voltammograms. Raloxifene was initially oxidized to reactive phenoxyl radicals, followed by a series of transformation steps leading to different final products in different pH media. A parallel-consecutive reaction mechanism was proposed for the pH-dependent formation of 7-hydroxyraloxifene, raloxifene 6,7-o-quinone and two raloxifene dimers, each pathway following a complex electrochemical-chemical mechanism. Both raloxifene diquinone methide and its N-oxides were not detected by in situ UV–vis spectroscopy and XPS analysis. This work provides an electrochemical viewpoint and comparable information for better understanding of the oxidative metabolism and chemical toxicology of raloxifene under physiological conditions in vivo or in vitro. [Copyright &y& Elsevier]

Abstract: The ability to in situ monitor the formation and transition of soluble corrosion products generated during metal electrochemical processes is important for elucidating the corrosion mechanism. The combination of cyclic voltammetry and cyclic voltabsorptometry allows simultaneous measurements of the potential-dependent current and absorbance, the latter of which corresponds to the characteristic wavelength of each light-absorbing species. For this purpose, a long-optical-path thin-layer electrochemical cell (LTE-cell) was fabricated to study the corrosion inhibition of copper by phytate in alkaline media. A conventional electrochemical cell was also used for common cyclic voltammetry and impedance spectroscopy. The morphology of the corroded copper surfaces was characterized using field-emission scanning electron microscopy. A high corrosion inhibition efficiency (ca. 90%) of phytate on copper was achieved in 0.1moldm−3 NaOH solution. Phytate was shown to promote the formation of the soluble intermediate cuprous ions and hinder the generation of the cupric ions from pitting corrosion of the initially deposited cuprous oxide layer. The integrity of the cuprous passive layer was therefore maintained, which strongly suppressed further formation of various cupric corrosion products. The results of this study indicate that cyclic voltabsorptometry based on a LTE-cell is an effective method for studying metal corrosion processes that involve light-absorbing ions. [Copyright &y& Elsevier]

Abstract: This paper describes a novel method of obtaining cyclic voltammograms (CVs) from optical signals. The obtained CVs correspond to the various specific species involved in the electrode process, which give more detailed information on the system under investigation than the common CV. For this purpose cyclic voltabsorptometry was used to investigate the successive oxidation processes of rutin on a graphite-wax electrode by using a long optical-path thin-layer electrochemical cell. The dynamic UV spectra of rutin showed the information on the structures of the oxidation products at different potentials. Cyclic voltabsorptiograms (CVAs) were measured in three potential ranges at the characteristic absorption wavelengths of rutin, 346, 254 and 296nm, respectively. The CVs of three species in solution (rutin and its two products) were obtained from the derivative cyclic voltabsorptiograms (DCVAs). Based on this the redox mechanisms of rutin in different CV peaks were discussed. [Copyright &y& Elsevier]