AMPEROMETRIC DETECTION WITH MEMBRANE-BASED SAMPLING FOR PERCENT-LEVELDETERMINATIONS OF ETHANOL

Ethanol present in solutions was determined by extracting ethanol vapo r 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 w as employed. Three- and four-step potential waveforms were evaluated f or use in quiescent solutions. Cyclic voltammograms and pulsed amperom etric detection calibration curves recorded with a platinum rotated di sk electrode at 0 and 400 rpm. were used to optimize potential wavefor ms. A four-step waveform was insensitive to solution hydrodynamics and was suited for ethanol detection in a thin, static solution layer beh ind a membrane. The four-step waveform was useful for detecting ethano l over a wide concentration range (0.02 mM to 1.7 M). The membrane's a bility to block transport of non-volatile species and the method's wid e detection range permitted the determination of ethanol directly from non-diluted samples of beer, pre-mixed cocktail, and wine.