Rapid and effective sample clean-up based on magnetic multiwalled carbon nanotubes for the determination of pesticide residues in tea by gas chromatography-mass spectrometry.

In this work, amine-functionalised magnetic nanoparticles and multiwalled carbon nanotubes (MNPs/MWCNTs) composites were synthesised by a simple method and applied as an adsorbent for rapid clean-up of acetonitrile extracts of tea samples prior to analysing eight pesticide residues by gas chromatography-mass spectrometry. Several parameters affecting the sampling and treatment efficiency were investigated, including extraction solvent, sonication time, weight ratio of MWCNTs to MNPs in the composites, amount of adsorbent, clean-up time and washing solution. Under the optimised conditions, the recoveries obtained for each pesticide ranged from 72.5% to 109.1% with relative standard deviations lower than 12.6%. Limit of quantification ranged from 0.02 to 0.08 mg kg⁻¹. The established method was successfully applied to the analysis of pesticide residues in real tea samples. The results indicated that the use of MNPs/MWCNTs composites allowed the simple and expeditious clean-up of complex tea samples for subsequent determination of pesticide residues.