Deep eutectic solvents vs. Aqueous acids in metal extraction from animal tissues

This study is the first to thoroughly compare the efficiency of ultrasonic extraction of heavy metals (Cu, Cd, Co, Cr, Fe, Pb and Zn) from solid-phase food products using acidic deep eutectic solvents and saturated aqueous solutions of these acids (lactic, citric, tartaric, glycolic, malonic, malic). Atomic emission spectral analysis with inductively coupled plasma is used for the sensitive and selective determination of metals in extracts. The work shows that eutectic solutions more effectively extract all the studied metals compared to aqueous solutions of acids (extraction efficiency of 85-95 %), which is comparable to the results obtained with complete mineralization of the sample using microwave mineralization. However, the proposed procedure is much more environmentally friendly, since it does not require oxidizing mixtures and does not generate dangerous nitrogen oxides. The highest extraction efficiency is achieved when using lactic acid. Also, in the work, the extraction mechanism was studied for the first time, and the contribution of choline chloride to the extraction efficiency was demonstrated. The proposed method made it possible to determine metals at a level from 0.33 to 0.8 mg kg-1, and was used to analyze real samples of chicken meat and certified reference material of beef liver.