Potassium ferricyanide ([Fe(CN)6]3-) reduction and ferrocenemethanol (Fc-OH) oxidation at a β-cyclodextrin (β-CD)-modified gold electrode were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) in phosphate buffer pH 7. CV and SECM experiments demonstrated that the surface of the modified electrode represents an insulating substrate for ferricyanide and a conductor substrate for Fc-OH. This difference is explained by the fact that Fc-OH can enter into the β-CD cavity forming an inclusion complex; on the other hand, ferricyanide is larger than the cavity of β-CD and so it cannot form an inclusion complex. Using the high sensitivity of the electron transfer of ferricyanide to the modification of the gold surface with β-CD, we selected this reaction as a probe to study the different modification stages at this modified electrode. When the electrode was partially modified, it was possible to obtain an adequate microscopic discrimination by using approach curves at different tip positions showing a nonhomogeneous surface. SECM images obtained from bare and partially and totally modified electrodes show very good resolution with different topography or null according to the extent of modification. When the modification was total, a homogeneous current with a regular topography was found, but when the modification was intermediate the topography was very irregular. To our knowledge, this is the first electrochemical study of a thiolated β-CD layer adsorbed on a gold electrode by SECM, and taken together, these results demonstrate that while the CV experiments give overall information about the studied surface, the SECM experiments permit microscopic characterization of the layer.

Artículo de publicación ISIA new, sensitive, reproducible and easy-to-use flow-injection method for determining nifuroxazide based on adsorptive stripping linear sweep voltammetry over screen-printed carbon electrodes is presented. The presented method is the first report of Nifuroxazide determination using a screen printed electrode and FIA and it is useful for pharmaceutical quality control, specifically, it could be adopted as an effective portable tool for on the shelf quality control at pharmacies.Limits of quantification (LOQ) and detection (LOD) as low as 42 and 10 ng/mL, respectively, were found. An average recovery of 100.7%, and a standard deviation of 2.5 % indicates acceptable accuracy and precision validating the proposed method.FONDECYT (Grant No. 1090120), the AIQB Chair at the University of Huelva and PAIDi from Junta de Andalucí

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The electrochemical reduction of a series of b-nitrostyrene and b-methyl-b-nitrostyrene derivatives by tast and differential pulse polarography and cyclic voltammetry over a wide pH range was studied. The reduction potentials are sensitive to the electronic properties of the para-substituent and to the substitution at Cb. An increase in the electron-donor properties of the substituent at the para position makes the reduction potential more negative. On the other hand, the reduction potential shifts several tens of millivolts towards more negative potentials on going from b-nitrostyrene to b-methyl-b-nitrostyrene derivatives, due to the decrease in conjugation with the increase in the C1-Ca torsion angle. A linear correlation between the calculated electronic barrier and the half-wave potential was observed. Furthermore, a linear correlation between the Hammett | p substituent constant and the half-wave potential also was observed, demonstrating that the electrochemical behaviour of these derivatives depends primarily on molecular structure and electron density distribution in a way similar to rates and equilibrium of homogeneous chemical reaction. The b-nitrostyrenes studied illustrate nicely the effects of steric and electronic effects on electrochemical reactions.