Desenvolvimento de plataforma portátil e de baixo custo para determinação de sulfeto em águas utilizando smartphones e impressão 3D

Abstract

The presence of the sulfide anion (S2-) in several types of water is undesirable due to its high toxicity and corrosive proprieties. Besides, its characteristic unpleasant odor - due to the formation of H2S - can be perceived in a concentration of 0.05 mg L-1 and when reaching the concentration of 100 mg L-1 is no longer perceptible due to fatigue of the olfactory system sensitive. Several analytical methods have been developed to quantify sulfide in solutions (S2-), however due to its high reactivity it is preferable that portable and low-cost methods are used to enable quantification in situ, reducing analytical errors related to sampling steps and transport to the laboratory. Here, a modular platform built with 3D printing was developed for in situ determination of sulfide in waters using the phenomenon of fluorescence and treatment of digital images. The analytical method is based on the generation of gaseous H2S through the addition of H3PO4 in the solution containing sulfide followed by the diffusion of the gas through a porous membrane and collected by the reagent Mercury fluorescein acetate (FMA). The reaction between FMA and sulfide causes suppression of fluorescence with maximum emission at 535 nm (green color) when excited at 470 nm (blue region). LED with maximum emission at 470 nm was used as a radiation source and a smartphone was properly positioned to acquire digital images of the fluorescent reagent. The optimized conditions resulted in a linear relationship for sulfide in the range of 0.5 to 5.0 µmol L-1 with an analysis time of 20 minutes and 25ºC (room temperature) and 10 mL of sample. Recoveries between 98.0 and 107.4% were obtained. Although AFM has already been used for sulfide determination, the combination of the vapor generation approach with a reduced amount of reagent and digital imaging has been demonstrated for the first time.