Electrochemical oxidation mechanism of eugenol on graphene modified carbon paste electrode and its analytical application to pharmaceutical analysis.

Electrochemical properties of eugenol were investigated on a graphene modified carbon paste electrode (CPE) by using voltammetric methods, which exhibited a well-defined irreversible peak at about 0.7V vs Ag/AgCl, NaCl (3M) in Britton-Robinson buffer at pH 2.0. Mechanism of the electrochemical reaction of eugenol was studied by performing density functional theory (DFT) computations and mass spectroscopic analysis. (CPCM:water)-wB97XD/aug-cc-PVTZ//(CPCM:water)-wB97XD/6-31G(d) level calculations predicted that the formation of product P2, possessing a para-quinoid structure, is preferred rather than the product P1, suggested in the literature, having an ortho-quinoid system. Determination of eugenol in a pharmaceutical sample was realized in the light of the electrochemical findings, and a validated voltammetric method for quantitative analysis of eugenol in a pharmaceutical formulation was proposed. The differential pulse voltammogram (DPV) peak currents were found to be linear in the concentration range of 1.0 × 10-7 to 1.7 × 10-5M. The limit of detection (LOD) and the limit of quantification (LOQ) were obtained to be 7.0 × 10-9 and 2.3 × 10-8, respectively.

Voltammetric determination of nitrite in meat products using polyvinylimidazole modified carbon paste electrode.

A simple and sensitive voltammetric method was developed to determine the amount of nitrite by using Carbon Paste Electrode (CPE) which is modified with polyvinylimidazole (PVI). A buffer solution of phosphate with a pH 4 value was used in the experiments. The amount of the nitrite-ion was determined by cyclic voltammetry (CV). The electro-chemical behaviour of nitrite-ion was investigated by using CV on the PVI modified CPE. A well-defined oxidation peak was obtained at 0.83 V against a reference Ag/AgCl electrode. Differential pulse voltammetry (DPV) was applied for the calibration plot and for the detection limit. The optimisation procedure was done in two steps: using a two-level factorial design for preliminary evaluation of the contributing factors, and the Box-Behnken Design (BBD) to assess the optimal experimental conditions. These are done with the analysis of 3 different factors in 15 runs of DPV. The optimum conditions are obtained within a linear response range of 5×10(-7)-1×10(-4) mol L(-1). Regression analysis is performed within this range showed the linear equation of y=0.028x+3.93×10(-7) with r(2)=0.9982, and for n=7. Limit of Detection (LOD) was 9×10(-8) mol L(-1) with S/N=3, and Limit of Quantification (LOQ) was 3×10(-7) mol L(-1) with S/N=10. The procedure was used successfully to detect the amount of nitrite in meat products.