Estratégia de pré-concentração em papel para determinação de ferro em etanol combustível

Abstract

Among the organic and inorganic contaminants inserted in the composition of fuel ethanol, transition metals, such as iron, have great catalytic power in the peroxidation of hydrocarbons present in gasoline or even in the oxidation of engine components, which may compromise the its efficiency even at low concentrations. The officially employed in the control of these contaminants require specialized analysts or even the application of separation and preconcentration methods such as solid phase extraction (SPE). Thus, the search for simple, portable, sensitive and low-cost methods is important to facilitate the monitoring of inorganic contaminants present in trace concentrations in fuels. The present work describes an alternative in-paper preconcentration procedure for the determination of Fe3+ in fuel ethanol. The preconcentration strategy was based on the sequential addition of Fe3+ aliquots in the hydrophilic zone of paper-based microfluidic analytical devices (μPADs), which were constantly heated using a heating system for evaporation of volatile sample components. The detection and quantification of the analyte were based on the colorimetric reaction between Fe3+ and SCN-, obtaining a characteristic red complex. The images were captured by a smartphone, 10 minutes after the start of the reaction, and the data were analyzed in the RGB scale through the ImageJ program, being related the concentration of Fe3+. In the preconcentration stage, the diameter of the μPAD used (20 mm), the number and the volumes of the added Fe3+ and SCN-aliquots (40 aliquots of 25 μL and 1 aliquot of 25 μL, respectively) were optimized and the temperature of the heating system (T = 90 ° C). A linear response in the range of 5 to 30 mg L-1 of Fe3+ was observed, with a coefficient of determination of 0.9937, a coefficient of variation of 1.89%, a visual detection limit of 5 mg L-1 and a preconcentration factor of 33.6. With these characteristics, the procedure presented advantages such as low reagent and sample consumption, and consequently, reduction of generated waste, besides portability (which facilitates the application in remote areas) and the reduced cost.