Digital image method based on smartphone assisted by hydrophobic natural deep eutectic solvent for Iron quantification in dietary supplements

Abstract

Quality control in dietary supplements is necessary to ensure its safety and effectiveness due to its wide consumption. Conventional methods often include the use of toxic solvents, complex, high power consumption and expensive instrumentation, limiting their applicability for on loco analysis and imputing low green metrics. In this work, an innovative and environmentally friendly analytical method was developed and validated, combining hydrophobic natural deep eutectic solvents (NADES) and digital colorimetric detection via smartphone. The NADES, formulated with menthol and dodecanoic acid precursors with a molar ratio of 1:1 was enabled selective and efficient extraction of Fe³⁺ using an ion-pair complex SDBS-MB (Sodium Dodecylbenzenesulfonate-Methylene Blue) colorimetric reagent, eliminating complex steps and hazardous compounds. This reaction mechanism, assisted by a hydrophobic NADES, has not been previously reported for Fe quantification. Under optimized conditions (10 min / 15 mL), the method achieved a limit of detection (LOD) of 31 µg L⁻¹, and a limit of quantification (LOQ) of 103 µg L⁻¹, with recoveries ranging from 92.0% to 106%. Statistical tests indicated equivalence in variance and average from analysis of total Fe in dietary supplements when compared to UV-Vis spectrophotometry methods. In addition, the method reached a green score of 0.84, demonstrating to be a green analytical method. This portable and cost-effective approach represents a significant advancement for green methods, useful for quality control of supplements, as well as potential application to other matrices. In fact, the method presents a high selectivity for Fe in presence of several inorganic and organic compounds with a good sensitivity and selectivity.