Analysis of the Composition of Water–Alcohol Mixtures Using the Infrared Absorption Spectra of their Vapor

The IR absorption spectra of the saturated vapor of alcohols and alcohol-containing mixtures in the region of 1.5–1.3 μm were investigated. A method based on multiple linear regression was developed for quantitative determination of the composition of water–alcohol mixtures. The range of methanol concentrations in which the nonlinear dependence of the concentration of alcohols in the saturated vapors over the liquid mixture on the concentration of alcohols in the liquid mixture does not significantly affect the results of analysis of the composition of the mixture was established. A method was proposed and developed for the selection of wavelengths for multiple linear regression based on minimization of the mean-square error of determination of the concentration. By the developed methods it is possible with relatively inexpensive and accessible spectroscopic apparatus to determine small amounts (<1%) of methanol against a background of large amounts of ethanol and water