RGB color sensor for colorimetric determinations: Evaluation and quantitative analysis of colored liquid samples

In this work, a red, green, blue (RGB) color sensor was used for quantitative optical analysis of colored solutions. The capability of the sensor to respond to different colored solutions was critically evaluated to better understand which spectral bands are filtered and processed by each sensor channel. The effective capability of the RGB sensor, defined as its ability to illuminate and detect electromagnetic radiation reflected by the samples, was observed in the range of 415-564, 440-600 and 510-750 nm for blue, green and red channels, respectively. These results can help understand the interaction between the light emitted by the sensor and the signals obtained by the RGB channels for different quantitative determinations. In order to investigate the interaction between the RGB sensor and colored substances, and thereafter achieve quantitative optical analysis, different colored dyes were chosen to evaluate the RGB sensor capability, thus covering a wide range of colors. The analytical performance of the RGB sensor yielded a linear range of 5.0-50.0 μmol L^-1 for dye solutions. The accuracy of this sensor was demonstrated by the thiocyanate method for colorimetric determination of iron in soil and supplement samples. Such RGB sensor achieved analytical performance similar to that obtained with the commercial spectrophotometer, without requiring the use of computers for image processing so as to gather RGB values. Additionally, this sensor also contributes to meeting the requirements of Internet of Analytical Things (IoAT) for the quantitative analysis of colored solutions.