Voltammetric Sensor Based on the Poly(p-aminobenzoic Acid) for the Simultaneous Quantification of Aromatic Aldehydes as Markers of Cognac and Brandy Quality

Cognac and brandy quality control is an actual topic in food analysis. Aromatic aldehydes, particularly syringaldehyde and vanillin, are one of the markers used for these purposes. Therefore, simple and express methods for their simultaneous determination are required. The voltammetric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWCNTs) and electropolymerized p-aminobenzoic acid (p-ABA) provides full resolution of the syringaldehyde and vanillin oxidation peaks. Optimized conditions of p-ABA electropolymerization (100 µM monomer in Britton–Robinson buffer pH 2.0, twenty cycles in the polarization window of −0.5 to 2.0 V with a potential scan rate of 100 mV·s(−1)) were found. The poly(p-ABA)-based electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Electrooxidation of syringaldehyde and vanillin is an irreversible two-electron diffusion-controlled process. In the differential pulse mode, the sensor allows quantification of aromatic aldehydes in the ranges of 0.075–7.5 and 7.5–100 µM for syringaldehyde and 0.50–7.5 and 7.5–100 µM for vanillin with the detection limits of 0.018 and 0.19 µM, respectively. The sensor was applied to cognac and brandy samples and compared to chromatography.