DIRECT DETERMINATION OF ETHANOL AND METHANOL IN LIQUID SAMPLES BY MEANS OF VAPOR PHASE-FOURIER TRANSFORM-INFRARED SPECTROMETRY

A FTIR procedure is proposed for the direct determination of methanol and ethanol in liquid samples, such as alcoholic beverages and eau-de- cologne, based on vapor generation from small injected volumes of untr eated samples into a heated Pyrex glass reactor in which, at a tempera ture of 80 degrees C, ethanol and methanol are volatilized and introdu ced into a long-path IR gas cell by means of a N-2 carrier flow. The I R spectra obtained present two characteristic ethanol bands (1050 and 880 cm(-1)) and a single characteristic methanol band (1030 cm(-1)). T he measurement of the area of the transient recording obtained for the wavenumber range between 1025-950 and 950-820 cm(-1) allows us the de termination of ethanol and methanol in the same sample by using a simp le proportional equations approach. The limit of detection values foun d for an injection volume of 1 mu l were 0.21% v/v for ethanol and 0.0 4% v/v for methanol and the relative standard deviation values were be tween 0.5 and 1.4% for five analyses of samples containing between 30- 80% v/v of ethanol and 0.5-3.5% v/v of methanol. Acetone, ethyl acetat e, 1-propanol and 2-propanol do not interfere with this determination at concentration levels about those of methanol. (C) 1997 Elsevier Sci ence B.V.