This work describes the development of a voltammetric methodology based on a carbon paste electrode enriched with multiwalled carbon nanotubes and TiO2 nanoparticles, for the electrochemical quantification of diclofenac. All stages of the methodology were optimized by a Box-Behnken experimental design. The electrochemical behavior of diclofenac was studied by cyclic voltammetry. Results showed that the oxidation of diclofenac is favored by the presence of both MWCNT and TiO2 nanostructures since a considerable increase in the anodic peak current is observed when compared to a that obtained with a bare carbon paste electrode. Under the optimal values found and with the appropriate statistical analysis, a LOD of 0.33 μM, a LOQ of 1.11 μM, a linear concentration range from 1.1 × 10−6 to 5 × 10−3 M (R2 = 0.9958), and a sensitivity of 0.487 μA.μM−1 were found. The electrode’s response was precise as the reproducibility resulted to be 4.39% (%RSD). Finally, a study of possible interferences was performed, along with the quantification of diclofenac in pharmaceutical samples by the proposed voltammetric methodology. The voltammetric method was validated by comparing the results with those obtained with the UV–vis spectrophotometric method.

In literature, studying the effect of the working electrode's surface morphology on the electrochemical kinetics for various molecules has increased. An important parameter related to these studies is the electroactive area of the electrode. Generally, a model molecule such as ferro/ferricyanide is used to calculate the electroactive area by cyclic voltammetry at different scan rates and using the Randles-Sevcik equation. However, since the electrochemical phenomena depend on the electrode's nature and the transformed molecule, it is can be assumed that the electroactive area calculated with the ferro/ferricyanide molecule will not be representative when another molecule is transformed or another electrode is used. Therefore, in this work, a comparative study of the electroactive area of five different carbon-based electrodes is performed calculated considering the anodic or cathodic processes of different molecules (diclofenac, ferro/ferricyanide and ascorbic acid), and with the results obtained, establish possible differences and similarities when calculating the electroactive area of each electrode.

In this work we present the development of an optimized methodology based on differential pulse voltammetry for diclofenac quantification, using electrochemically activated carbon paste electrodes and multi-walled nanotubes carbon paste electrodes. Under the optimized experimental conditions, diclofenac presented linear response over the range of 10 -10 to 10 -4 M for both electrodes. The lower detection limits found were 0.001 and 0.29 μM for the paste electrodes with and without nanotubes respectively. The effect of common interferences on diclofenac current response was investigated. Finally the proposed methodology was validated comparing the results obtained measuring the concentration of diclofenac in pharmaceutical samples with those obtained with the reference methodology.

Aflatoxins are high-toxic secondary metabolites of Aspergillus fungus, which contaminate food at trace levels. Promising voltammetric methods were developed using mercury electrodes, however, they have negative effects on the environment. This work proposes the development and optimization of a differential pulse voltammetric methodology for the quantification of Aflatoxin B1 through bismuth film electrodes by the reduction of aflatoxin. Aflatoxin B1 reduction is controlled by its diffusion towards the electrode’s surface. Optimal conditions for the preparation of the bismuth film and differential pulse voltammetry were obtained by Box-Behnken experimental designs, considering the maximization of the Aflatoxin B1 cathodic peak current. The LOD and LOQ resulted to be 11.2 ng l−1 and 37.3 ng l−1 respectively. The values for the reproducibility and repeatability as %RSD, using a 38.46 ng l−1 solution of Aflatoxin B1 for the measurements, were 5.3% and 4.6%, respectively. The proposed methodology was statistically validated using certified Aflatoxin B1 standard solutions and milk samples successfully analyzed, demonstrating that the proposed methodology represents a novel, low-cost, environmentally-friendly approach for the quantification of Aflatoxin B1.

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