Um método quimiluminescente baseado em imagens digitais para determinação de Cr (VI) em águas usando um sistema fluxo batelada.

Abstract

In this work, it is proposed a digital image-based chemiluminescent (DIB-CL) method that employs a flow-batch analyzer (FBA) for the determination of Cr (VI) in water. The proposed DIB-CL-FBA (Digital Image-Based Chemiluminescent Flow-Batch Analyser) system uses a webcam with CCD sensor for acquisition of digital images generated according to the RGB (Red-Green-Blue) colour system. In Cr (VI)determination, this specie is quantitatively reduced to Cr (III) by using hydrogen peroxide in acid medium. After, the produced chromium (III) actuates as catalyst effect on oxidation of the luminol by hydrogen peroxide in alkaline medium, yielding chemiluminescence radiation. The emitted light is captured by webcam generating a digital image, in which a region is delimited in order to retrieve the values of the R, G and B individual components of each pixel. These values are used to define a position vector in RGB three-dimensional space. The vector norm is adopted as the RGB-based value (analytical response), which is linearly related o the analyte concentration. A linear response range for implementing the Cr (VI) determination was from 7.36 to 150.00 μg L−1.The linear analytical curve was validated through ANOVA, F-test for lack of fit and graphical analysis of the residue left by the model. The limits of detection and quantification estimated were 2.20 and 7.36 μg L-1, respectively, and sampling rate was found as 40 h-1. The results of applying the DIBFBA- CL method were compared with those obtained using a spectrophotometric method used as reference. It was verified that there is no statistically significant systematic difference between the results by applying the paired t-test at a confidence level of 95%.