Amperometric detection with membrane-based sampling for percent-level determinations of ethanol

Ethanol present in solutions was determined by extracting ethanol vapor through an expanded poly(tetrafluoroethylene) (e-PTFE) membrane into a small volume of aqueous electrolyte (0.1 M H2SO4) and detecting the analyte amperometrically. A pulsed electrochemical detection scheme was employed. Three- and four-step potential waveforms were evaluated for use in quiescent solutions. Cyclic voltammograms and pulsed amperometric detection calibration curves recorded with a platinum rotated disk electrode at 0 and 400 rpm. were used to optimize potential waveforms. A four-step waveform was insensitive to solution hydrodynamics and was suited for ethanol detection in a thin, static solution layer behind a membrane. The four-step waveform was useful for detecting ethanol over a wide concentration range (0.02 mM to 1.7 M). The membraneʹs ability to block transport of non-volatile species and the methodʹs wide detection range permitted the determination of ethanol directly from non-diluted samples of beer, pre-mixed cocktail, and wine.