Analytical method for 44 pesticide residues in spinach using multi-plug-filtration cleanup based on multiwalled carbon nanotubes with liquid chromatography and tandem mass spectrometry detection.

Spinach is one of the most commonly planted vegetables worldwide. A high chlorophyll content makes spinach a complicated matrix in pesticide residue analysis. In this study, a rapid clean-up method was developed for the analysis of pesticide multi-residues in spinach followed by liquid chromatography with tandem mass spectrometry. A modified QuEChERS method with multiwalled carbon nanotubes and carbon material was adopted in the multi-Plug Filtration Cleanup procedure. This method was validated for 44 representative pesticides spiked at two concentration levels of 10 and 100 μg/kg. The pesticides of different physicochemical properties were registered on spinach in China. The recoveries were between 76 and 114% for major pesticides with relative standard deviations of less than 15%, except for quizalofop-P-ethyl, pyrimethanil, and carbendazim. Matrix-matched calibration curves were performed with the coefficients of determination higher than 0.995 for the studied pesticides for concentration levels of 10-500 μg/kg. The limits of quantitation ranged from 2 to 10 μg/kg. The developed method was successfully applied to determine pesticide residues in Chinese market spinach samples.