A digital image-based method employing a spot-test for quantification of ethanol in drinks

Abstract

A low-cost analytical method for quantification of ethanol in drinks based on the combination of a colorimetric spot-test and a digital image-based (DIB) method is proposed. The digital images from spot-test reactions were captured using a digital camera in a portable plastic chamber designed with internal lighting control. The images were decomposed by a RGB approach using freely available software. The R channel showed the best linearity, with two linear ethanol concentration ranges: from 1.0% to 20.0% v/v (r = 0.999) and from 25.0% to 50.0% v/v (r = 0.980), with limits of detection and quantification of 0.25% and 0.85% v/v, respectively, for the first analytical curve. The developed method was applied to quantification of ethanol in alcoholic drink samples with results in close agreement with those obtained using a spectrophotometric method at a confidence level of 95%, and with low waste generation (835 μL/spot-test). Thus, we believe that the DIB method can be useful with regard to environmental and social impacts, once the method has a low waste generation and uses an easily available instrumentation with potential for in situ determination during the alcoholic beverage production and its quality control.