Determination of Residual Concentration of Ionic Liquids with Different Anions and Alkyl-Chain Lengths in Water and Soil Samples.

Considering the wide synthesis and application of ionic liquids (ILs), the toxicity of ILs has recently gained growing attention. However, few studies focused on IL determination methods in environmental samples. In the present study, we implemented the determination methods for the 12 ILs with different chemical structures using high-performance liquid chromatography (HPLC) and ultraviolet (UV) spectrophotometry. The optimum conditions for extraction of ILs from soil samples were also obtained by single-factor experiments and response surface methodology (RSM). The instrument detection limits (IDLs) reached 10(-10) g. Compared to the use of UV, HPLC had the standard curve with stronger correlation (R(2) ≥ 0.999) and lower detection limit. We therefore used HPLC to detect the contents of ILs in water and soil samples. A standard adding method was used for the reliability test of the above methods. The average recovery in water samples was 90.46%-108.83%, and the coefficient of variation (CV) was 0.51%-9.07%. The method detection limits (MDLs) were below 0.1 mg/L. The optimized IL extraction conditions in soil samples were as follows: The ratio of methanol and saturated ammonium chloride was 90:10, the ultrasonic time was 50 min, and the power was 350 W. The average recovery in soil samples was 70.39%-85.30%, and the CV was 0.50%-9.99%. The MDLs were below 1 mg/kg. These results using the aforementioned methods met the standards of residue analysis. The present study can provide scientific analysis methods and a basis for evaluation of the study of IL residues in environmental samples.