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Sensitive and selective voltammetric sensors for the simultaneous quantification of natural phenolic antioxidants in cognac and brandy
* 1 , 2
1  Kazan Federal University, Kazan, Russia
2  Kazan Federal University
Academic Editor: Núria Serrano (registering DOI)

Aged distilled beverages namely cognac and brandy contain natural phenolic antioxidants to be considered as one of the quality markers. Different types of chromatography are usually applied for their quantification. Electrochemical sensors being simple, reliable and cost-effective could be an effective alternative tool for this purposes. The only problem of the electrochemical approaches is the low selectivity of phenolics determination due to the structural similarity of analytes. This limitation can be overcome using chemically modified electrodes. Novel voltammetric sensors based on the carbon nanotubes and electropolymerized pyrocatechol violet or p-aminobenzoic acid (ABA) have been developed for the simultaneous determination of phenolic antioxidants in cognac and brandy for the first time. Application of carbon nanotubes (polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes (f-SWNT/GCE) and multi-walled carbon nanotubes (MWNT/GCE)) as a substrate provide high surface area and conductivity while polymeric film provides structural similarity to the analytes and the porous structure leading to the increase of the determination sensitivity. Polymerization conditions of pyrocatechol violet and ABA in potentiodynamic mode has been optimized. Sensors has been characterized with SEM, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The polymeric films exhibit porous structure with the shape of particles and their aggregates deposited on the surface of carbon nanomaterials that confirms the successful electropolymerization. Statistically significant increase of the effective surface area and low charge transfer resistance of the sensors developed in comparison to GCE and GCE modified with carbon nanotubes have been obtained. Sensors developed have been applied for the simultaneous sensitive determination of gallic and ellagic acids as well as syringaldehyde and vanillin under conditions of differential pulse voltammetry. The analytical characteristics obtained are improved vs. other modified electrodes. The sensors selectivity in the presence of typical interferences and other natural phenolics has been obtained that is important advantage. The sensors developed have been successfully tested on the cognac and brandy samples. The results obtained agree well with chromatographic data confirming the accuracy of the sensors developed. Thus, the novel highly sensitive and selective voltammetric sensors for the simultaneous determination of structurally related phenolic antioxidants are characterized by simplicity of the fabrication, reliability, cost-efficiency and can be applied for the routine analysis as an alternative to chromatographic methods.

Keywords: Electrochemical sensors, carbon nanomaterials, electropolymerization, phenolic acids, phenolic aldehydes, aged distilled beverages