DEVELOPMENT AND VALIDATION OF ANALYTICAL METHODOLOGY BASED ON DIGITAL IMAGES OF SPOT TEST FOR DETERMINATION OF ETHANOL IN CACHAÇA

Abstract

In this work it is carried out the development, optimization and validation of analytical methodology for determination of ethanol in cachaça samples. The method was based on digital image analysis spot test performed with the analyte of interest, captured by a camera in a system built for this purpose. The principle of the method is measurement of tones obtained after the occurrence of the colorimetric reaction employing the RGB color model, color components which varies in proportion to the analyte concentration. For the determination of ethanol, it was employed the reaction of redox in which chromium (VI) is reduced to chromium (III) or chromium (II) and the ethanol is oxidized to acetaldehyde, generating change in the yellow-orange color to blue-green. By determining the ethanol content, a linear calibration curve in the range from 10 to 70% v/v ethanol was obtained, with a coefficient of determination r² = 0.9910 and limits of detection and quantification respectively equal to 1.72 % v/v and 5.74% v/v. Comparison of results for the cachaça samples analysis using the developed method and the reference method showed no significant differences between both methods, which were analyzed using the paired t-test, 95% confidence. The analysis of six cachaça samples showed that three of them had ethanol content outside the range permitted by law. Besides the image capture system is versatile and robust and can be used in situ analysis.