Determinação in situ de analitos de interesse alimentício empregando tratamento de imagens digitais de spot tests

Abstract

In this work a simple, fast and inexpensive analytical method was developed to carry out in situ determinations of ethanol and sulfite ions in food samples. The method was based on digital images captured by cameras and / or mobile phones, using a proper device for this purpose. Indirect colorimetry was employed, where it was measured the intensity of the light reflected by the solution, employing the RGB color model. The quantification of the analytes was performed by calibration curve method, using image processing software to obtain the numerical values for each one of the three primary colors (red (R), green (G) and blue (B)). In the first procedure, it was determined the ethanol concentration in drinks, obtaining limits of detection (LOD) and quantification (LOQ) of 0.25 and 0.85 %, respectively, with a linear calibration curve in the range from 1 to 20 % v / v (r = 0.999), using the R channel due to better linearity and results in close agreement to the spectrophotometric method used as reference method, with a confidence level of 95 %. The recovery study was carried out in six commercial samples and the recovery percentage ranged between 85.0 and 106%. The sulfite ions were determined in wines, vinegars and juices samples, with limits of detection (LOD) and quantification (LOQ) of 3.3 × 10-5 mol L -1 and 1.0 × 10 -4 mol L-1, respectively, and with a linear calibration curve from 1.0 × 10-4 to 3.0 × 10-3 mol L1 (r = 0.997) using the B channel supplying a good linearity and results in close agreement to the iodometric titration method employed as reference method, at a confidence level of 95 %. The recovery percentage of sulfite in commercial samples ranged between 84.4 and 103%.