Vapour generation–Fourier transform infrared direct determination of ethanol in alcoholic beverages

Abstract

A procedure is proposed for the direct determination of ethanol in alcoholic beverages. The method is based on the injection of small volumes of untreated samples into a heated Pyrex glass reactor in which, at a temperature between 80 and 100 °C, the ethanol is volatilized and introduced by means of a nitrogen carrier flow into a gas cell of an FTIR spectrometer. The measurement of the area of the flow injection recording, obtained from the absorbance of the transient signals, in the wavenumber range between 1150 and 950 cm^–1, allows the direct quantification of ethanol without water background problems and free from interferences from sugars, providing a limit of detection of 0.02% v/v and typical RSDs between 0.11 and 0.5% for five analyses of the same sample containing between 5 and 30% v/v ethanol. The sampling frequency of the method is 51 h^–1 and accurate results were obtained for different types of alcoholic beverages, from low-alcohol beers to wines and spirits.