Derivative Fourier transform infrared spectrometric determination of ethanol in alcoholic beverages

Abstract

A derivative Fourier transform infrared (FT-TR) spectrometric procedure was developed for the direct determination of ethanol in alcoholic beverages, from beers to spirit samples. The method is based on first-order derivative FT-IR measurements between the peak at 1052 cm −1 and the valley at 1040 cm −1, which are present in aqueous solutions and alcoholic beverages, by using a micro flow transmittance cell with ZnSe windows and a spacer of 0.029 mm. The method involves the accumulation of ten scans and provides accurate results in the determination of ethanol in alcoholic beverages without requiring any previous chemical treatment of the sample or a previous separation or extraction step. The limit of detection corresponds to 0.025% (v/v) and results obtained in the analysis of real samples of beer, wine, vodka, gin and whisky agree with those found by different reference procedures. For the determination of ethanol in beverages containing high concentrations of sugars, it is necessary previously to determine the sugar content by measuring the derivative value between 1164 and 1147 cm −1 and subsequently to correct the negative interference of sugars on the determination of ethanol between 1052 and 1040 cm −1.