Avaliação de sensores ópticos de baixo custo para aplicação em determinações fotométricas ambientais empregando dispositivos IoT’s portáteis

Abstract

The development of increasingly smaller devices with greater processing power represents undeniable technological advancement in current times. Such a movement points towards facilitated and widespread access to tools, components, and items specially designed for independent and creative development, at a high level of customization. Analytical chemistry finds great value in such advances by instituting the Internet of Analytical Things (IoAT). Given the variety of available options, studying each component, its limitations, and functionalities is necessary. The objective of this work was to evaluate light sensors for applications in low-cost colorimetric devices; thus, different photodiodes and a photoresistor were evaluated, highlighting their spectral ranges of best applicability. Some analytes of environmental interest were assessed, and the obtained figures of merit were compared to those obtained by UV-vis spectrophotometry. Using a portable photometer, a procedure for sulfide determination in samples obtained from water treatment stations in the Triângulo Mineiro region was applied, and the analytical characteristics obtained, such as linear range: 0.26 to 3,00 mg/L; Detection limit of 0.09 mg/L, and coefficient of variation of 4.77 for mid-point measures, considered comparable to those obtained by the official method. The developed system has 18 hours of battery autonomy, a microcontroller with an integrated screen and buttons for user operation, a LED (635 nm), and an LTR-329 sensor for absorbance measurements. Another system tested for colorimetric determinations consists of implementing the sensor to replace the detector of the traditional spectrophotometer. The applicability was demonstrated in urea determinations in liquid reducing agent samples, with the system achieving a CV = 3.34 and DL of 0,06% (w/v) reaching statistically equivalent determinations to the reference spectrophotometric method with 95% confidence in concentrations with linear responses between 0,2 and 3,0%.