Determination of Trace Heavy Metal Elements in Litterfall by Inductively Coupled Plasma Optical Emission Spectrometry after Extraction Using Choline Chloride-Based Deep Eutectic Solvents

Abstract

Developing a green, safe and accurate sample preparation method for the determination of trace metal elements in environmental samples is of great importance. Here, choline chloride-based deep eutectic solvents (DES) were used to extract the heavy metal elements from litterfall, and the target analytes were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). During the optimisation step, we investigated factors such as the type, ratio, dosage, extraction time, and extraction temperature of deep eutectic solvents. The DES system based on choline chloride and maleic acid presented the highest extraction efficiency of 92% for Cd, Cu, Zn, and Fe. The proposed method was validated for accuracy using GBW10087. The certified and indicated values were in good statistical agreement at a 95% confidence level. Excitingly, the method showed an extremely low detection limits of litterfall and the excellent repeatability. For comparison, the analytes were also treated with traditional acid digestion. According to T-test, there were no significant differences in the analysis results at a 95% confidence level. Furthermore, the method developed has an energy consumption that is only one-eighth of that required by the acid digestion method. Our works not only we present an environmentally friendly method for the determination of trace element concentrations in environmental samples, but also deepen the understanding of the DES systems.

Keywords: Deep eutectic solvent, ICP-OES, Heavy metal element, Litterfall