The determination of pesticides in tea samples followed by magnetic multiwalled carbon nanotube-based magnetic solid-phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry

A simple, rapid, and efficient method regarding ultrasound-assisted extraction combined with magnetic solid-phase extraction (UA-MSPE) by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was set up for the simultaneous determination of metalaxyl, napropamide and epoxiconazol in tea leaf samples. Magnetic amino modified multi-walled carbon nanotubes (m-MWCNTs-NH2) were successfully synthesized, and were characterized by using Fourier transform infrared spectrometry, scanning electron microscopy and vibrating sample magnetometry. In this experiment, the pesticides in the tea leaves were firstly extracted with acetonitrile under ultrasonic assistance, and were then subjected to MSPE for purification. Various experimental parameters such as the amount of adsorbent, extraction time, type and volume of desorption solvent, desorption time, pH and salt concentration were systematically optimized. Under the optimal conditions, both the method detection limit (0.02-0.05 ng g(-1)) and the limit of quantification (0.05-0.10 ng g(-1)) were satisfactory with high sensitivity. The recoveries of the three pesticides in distinct tea samples ranged from 75.1% to 101.2% and the relative standard deviation did not exceed 13.5%. In addition, the method has been successfully applied for the determination of pesticides in actual samples with satisfactory results.