Determination of Residues of 4 Fungicides in Fruit Juice by High Performance Liquid Chromatography with Dispersion Solid Phase Extraction Based on Magnetic Carbon Nanotubes Modified with Deep Eutectic Solvent

A method for the determination of residues of 4 fungicides by high performance liquid chromatography (HPLC) with dispersion solid phase extraction based on magnetic carbon nanotubes modified with deep eutectic solvent (DES) was proposed. Choline chloride and glycol were mixed at the molar ratio of 1∶2, which was heated by vortex with a magnetic agitator until the transparent DES was obtained. Magnetic carbon nanotubes modified with DES were prepared with 2 mL of DES and 0.4 g of magnetic carbon nanotubes. 5 mL of water was taken and placed in a centrifuge tube, and 200 μL of fruit juice sample and 16 mg of magnetic carbon nanotubes modified with DES were added. The mixture was extracted by ultrasound for 10 min and precipitated for 30 min under external magnetic field. The upper liquid was removed and 1 mL of ethanol was added. After vortex for 2.5 min, the mixture was passed through a 0.22 μm filter membrane. Four fungicides, including iprodione, fenarimol, myclobutanil, and kresoxim-methyl, in the filtrate were determined by HPLC. As shown by the results, linear relationships between values of mass concentration of 4 fungicides and the corresponding peak area were found in the range of 0.5-5.0 mg·L^-1, with detection limits (3S/N) of 0.04 mg·L^-1 for iprodione, 0.11 mg·L^-1 for fenarimol, 0.15 mg·L^-1 for myclobutanil and 0.16 mg·L^-1 for kresoxim-methyl, respectively. Test for recovery was made by the standard addition method, giving results in the range of 81.5%-98.9%, with RSDs (n=6) of the determined values less than 7.0%.