A multivariate optimization of a green ultrasound-assisted extraction method using a natural deep eutectic solvent...

This study presents the development of a green ultrasound-assisted extraction (UAE) method using a natural deep eutectic solvent (NADES) composed of malic acid and citric acid for the determination of Fe, Mn, and Zn in instant coffee samples by flame atomic absorption spectrometry (F AAS). The solvent ratio was previously optimized using a combination of factorial and Box-Behnken designs. A two-level full factorial design (2³) was employed to optimize the NADES-UAE method. Extraction was performed using 0.3 g of coffee, 5.0 mL of NADES, and 35 min of sonication. The method achieved detection limits of 0.26, 0.55, and 3.38 μg g^-1, for Zn, Mn, and Fe, respectively. Method accuracy was assessed using a certified reference material of green coffee, yielding recoveries ranging from 92.4 % to 112.3 %. The method was successfully applied to instant coffee samples, with metal concentrations ranging from 2.14 μg g^-1 (Mn) to 60.44 μg g^-1 (Fe).