Green and Efficient Determination of Iron(III) in Gasoline Using Microemulsion-Based Extraction and Digital Image Analysis

Iron-(III) contamination in gasoline, originating from production or storage, compromises fuel quality and engine performance by catalyzing oxidation reactions, promoting gum and sediment formation, and accelerating engine wear. Accurate monitoring of this contaminant is, therefore, essential for ensuring fuel stability and extending engine lifespan. Conventional analytical methods, such as Atomic Absorption Spectroscopy, although highly reliable, demand sophisticated instrumentation and labor-intensive sample preparation. In this study, a sustainable and innovative approach is proposed by combining extraction induced by microemulsion breaking (EIMB) with digital image analysis (DIA) for the determination of iron in gasoline. Exploiting the ethanol naturally present in Brazilian gasoline, microemulsions are formed without the use of surfactants, thereby simplifying the procedure and minimizing reagent consumption. Experimental conditions were optimized through a complete 2⁴ factorial design, leading to the use of isopropanol as a dispersing agent, 1.0 mol L^-1 HCl, an 8 min extraction time, and a breaking volume of 500 μL. Quantification was performed using smartphone-based DIA, achieving a linear range of 0.3-10 mg L^-1 and a detection limit of 0.3 mg L^-1. Recovery tests on spiked gasoline samples confirmed the method's reliability, with recovery rates ranging from 97.4% to 116.2%. By reducing reagent use, eliminating toxic surfactants, and enabling low-cost, accessible analysis, the proposed EIMB-DIA strategy aligns with Green Chemistry principles and represents a significant advance in sustainable analytical methodologies for complex fuel matrices.