Indirect Determination of Liquor Alcohol Content Based on Near-Infrared Spectrophotometry

Alcohol is a key technical indicator of liquor, a favorite of consumers as a daily drinking. A simple and fast detection method for ethanol in liquor can help to improve the efficiency of a liquor inspection. Spectroscopy with the advantages of rapid and non-destructive can provide help for the analysis of ethanol content. Based on the good absorption effect of water molecules on infrared light, this paper explored the feasibility of indirect analysis of ethanol content in liquor by near-infrared spectrophotometry. By studying the effect of the optical path on the UV-VIS-NIR absorption spectra of water and ethanol, it is found that water molecules have an independent absorption peak at 1 448 nm. This absorption peak has a mutational point under the optical path of 10 mm. However, when the optical path is reduced to 1 mm, the shape of the absorption peak becomes symmetric and smooth, bringing the possibility of quantitative analysis. The absorption peak of aqueous ethanol solution in the range of 1 000 similar to 1 800 nm regularly decreases with the increase of ethanol content. It shows that the force between ethanol and water molecules do not affect their absorption spectrum. The linear equation between absorbance and alcohol content is obtained: A=1. 38-0.013m% (R-2 =O. 996 7) by extracting the absorbance at 1 448 nm. However, the fitting effect has a large relative deviation when the alcohol content is lower than 20% or higher than 80%. A better linear fitting equation with an excellent fitting effect is obtained; A=1. 40-0. 014m% (R-2 =0. 999 3) after adjusting the fitting range to 20%similar to 80%. The reliability of this method was tested through some purchased bulk and brand liquors. The results obtained by this method show a small relative deviation with the alcohol content marked on brand bottles, which is within the allowable error range of absorption spectrum analysis. Moreover, there are large relative deviations in the test measurement results of part of bulk liquors, which may be caused by the weaker quality control of bulk liquor. To some extent, this method has good accuracy and precision in detecting the alcohol content of liquor. This method has the advantages of convenience, rapid, no auxiliary reagent and wide linear range. It can be used as a test method for quickly analyzing the alcohol content of liquor.