The determination of ethanol in wine by voltammetry with an internal standard

A rapid method for the electroanalysis of ethanol is presented that incorporates flow extraction at room temperature, with voltammetric detection and potassium ferrocyanide [K₄Fe(CN)₆] as internal standard. In 0.1 M NaOH electrolyte, ethanol was oxidised at a platinum comb-shaped working electrode at −300 mV (vs. a Ag/AgCl reference electrode) and K₄Fe(CN)₆ was oxidized at +180 mV. The ratio of the anodic peak currents was linear with ethanol concentration in the range of 0.1 to 8.0% (v./v.), and the detection limit (calculated as 3 σ background) was 0.012 % (v./v.) for Osteryoung square wave voltammetry (OSWV) and 0.023 %(v./v.) for cyclic voltammetry (CV). The average extraction efficiency of ethanol from aqueous solutions, at 20 ± 1°C, was 8.5%. The repeatability was in the range of 2.5 to 3.3% RSD (n = 8), and accuracy was in the range of 95.2 to 104.7% for the determination of wine samples. Application to wines compared well with GC and HPLC methods and the nominal ethanol concentration determined by gravimetry. Analytical parameters in CV and OSWV are optimized, and the dependence of the extraction efficiency with temperature and nitrogen gas flow is presented.