Biosensing Membrane Base on Ferulic Acid and Glucose Oxidase for an Amperometric Glucose Biosensor.

A biosensing membrane base on ferulic acid and glucose oxidase is synthesized onto a carbon paste electrode by electropolymerization via cyclic voltammetry in aqueous media at neutral pH at a single step. The developed biosensors exhibit a linear response from 0.082 to 34 mM glucose concentration, with a coefficient of determination R2 equal to 0.997. The biosensors display a sensitivity of 1.1 µAmM-1 cm-2, a detection limit of 0.025 mM, and 0.082 mM as glucose quantification limit. The studies reveal stable, repeatable, and reproducible biosensors response. The results indicate that the novel poly-ferulic acid membrane synthesized by electropolymerization is a promising method for glucose oxidase immobilization towards the development of glucose biosensors. The developed glucose biosensors exhibit a broader linear glucose response than other polymer-based glucose biosensors.

UV-visible spectroscopic and electrochemical study of the complex formation between Fe(II) and 5-amino-1,10-phenantroline (5-Aphen) in aqueous solution.

The system Fe(II)-5-Aphen-H(2)O was studied. The spectroscopic and electrochemical results show that only one stable complex between Fe(II) and 5-Aphen forms, having a 1:3 stoichiometric ratio. The spectrophotometry study allowed determination of the formation constant of the complex (logbeta(3)=23.42+/-0.06). Also, the stability of the complex was evaluated as a function of pH; it was found that it decomposed at low pH values depending on the concentration and a pseudo-first order kinetics constant associated with k'=0.011min(-1). The results are in agreement with the electrochemical behaviour observed in the system, which indicated that at pH 1.33 the destruction of the complex [Fe(5-Aphen)3](2+) took place as a function of time; however, when the experiments were carried out at pH 6.19 the complex was stable. The thermodynamic data obtained through the use of MEDUSA allowed construction of predominance zone diagrams of the system Fe(II)-5-Aphen-H(2)O under the experimental conditions used. The thermodynamic results represented in the PZD describe the experimental behaviour reported in this work.

Spectroscopy study of 5-amino-1,10-phenanthroline.

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry.

This work reports the use of alpha and beta-cyclodextrin-modified carbon paste electrodes (CPE(alpha-CD) and CPE(beta-CD)) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE(beta-CD )exhibited a better analytical response that the CPE(alpha-CD), while the detection limits obtained for Pb(II) were 6.3 x 10(-7) M for the CPE(alpha-CD) and 7.14 x 10(-7) M for the CPE(beta-CD), whereas for Cd(II) they were 2.51 x 10(-6) M for the CPE(alpha-CD) and 2.03 x 10(-6) M for the CPE(beta-CD).