Improvement in the performance of an electrochemical sensor for ethanol determination by chemical treatment of graphite

The present work describes the preparation and characterization of chemically treated graphite by different strategies and its use for the construction of nickel-based electrochemical sensors for ethanol determination. Chemical treatment of graphite powder was carried out under three different conditions: with nitric acid, with piranha solution (98% sulfuric acid and 30% hydrogen peroxide in the ratio of 70:30) and by the Hummers method. Treated and untreated graphite samples were characterized by scanning electron microscopy techniques (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FFIR), x-ray diffraction (XRD) and thermogravimetry (FO). Surface chemical groups were estimated by Boehm titration. Carbon paste electrodes were constructed using untreated and treated graphite and evaluated for adsorption of nickel ions. After that, exploring the catalytic proprieties of redox pair Ni(II)/Ni(III) the device was applied towards ethanol oxidation. From all chemical treatments evaluated, samples of graphite treated by the Hummers method presented the best analytical performance. Using the best set of experimental conditions, it was observed a linear dynamic range (LDR) between 50 and 1000 mu mol L-1. with a sensitivity of 42.1 mu A L mmol(-1) and limit of detection (LOD) and quantification (LOQ) of 15 and 50 mu mol L-1, respectively. The electroanalytical application of the sensor was performed for ethanol quantification in four distilled beverage samples (vodka, cachaca, pisco and whiskey) using amperometry. The obtained results agree with a comparative method at a confidence level of 95%. Repeatability studies for five different electrodes showed an RSD of less than 10%.