Ultra-fast microwave-assisted digestion in choline chloride-oxalic acid deep eutectic solvent for determining Cu, Fe, Ni and Zn in marine biological samples

A green and very fast method for digestion of biological marine samples in choline chloride-oxalic acid deep eutectic solvent under microwave radiation was developed. These samples were then used for the determination of Cu, Fe, Ni, and Zn by inductively coupled plasma-optical emission spectrometry (ICP-OES). Key parameters that influence analyte recovery were investigated and optimized using the fish protein certified reference material (DORM-3). Features of the sample preparation method include: (a) microwave assisted dissolution of the samples in deep eutectic solvent at atmospheric pressure in just 20 s, (b) addition of 7.0 mL HNO3 (2.0 M) to the cooled solution, and (c) centrifugation, filtration and dilution of the solution to a predetermined volume before being subjected to analysis by ICP-OES. The Student's t-test (P = 0.05) showed excellent agreement between the obtained results and the certified values, the recovery of all the elements being greater than 96.1%. The proposed method was successfully applied in the determination of analytes in marine samples (fish muscle and liver tissues, and macroalgae). For comparison, a conventional acid digestion method was also used. The simplicity of the procedure, high extraction efficiency, short analysis time, absence of concentrated acids and oxidizing agents, and the use of safe and inexpensive components describe the high potential of the proposed method for routine trace metal analysis in biological samples.