In situ eutectic mixture combined with diluted organic acids for a greener ICP-OES elemental analysis of chocolate

Chocolate is a complex, highly-fat matrix, whose elemental analysis typically relies on microwave-assisted acid digestion (MW-AD) with concentrated HNO₃ and H₂O₂ under harsh conditions. In this study, a greener sample-preparation strategy was developed by combining thymol, a natural lipid extractor, with a diluted aqueous solution of methanesulfonic acid (MSA) for elemental extraction. The process involves the in situ formation of a deep eutectic phase between thymol and lipid constituents. After heating and centrifugation, a multiphase system forms, from which the aqueous phase containing the analytes was collected for ICP-OES determination. Experimental conditions were optimized using univariate and multivariate approaches, considering acid concentration, lipid extractor, sample mass, extraction time, temperature, acid volume, and thymol mass. Efficient extraction of Mg, Ca, Mn, Ni, Cu, and Zn was achieved using 1.0 g of sample, 1.5 g of thymol, and 3.0 mL of 0.5 mol L^-1 MSA solution at 80 °C for 30 min. For these analytes, no significant matrix effects were observed for white, milk, and dark chocolates, with recoveries ranging from 79 ± 2 to 111 ± 5%. In contrast, Fe showed lower recoveries (25 ± 1-72 ± 3%), indicating poor partition to the aqueous phase. Linear responses (r ≥ 0.998) were obtained by internal standardization with Ga and Y, with limits of detection ranging from 1 μg kg^-1 (Cd) to 280 μg kg^-1 (Ca). The results agreed with the reference MW-AD procedure at the 95% confidence level. AGREEprep = 0.59 and Analytical Eco-scale = 90, versus 0.28 and = 75 for MW-AD procedure, reflected the lower energy demand, reduced consumption of hazardous reagents, and lower waste generation.