Carbon nanotube-based QuEChERS extraction and enhanced product ion scan-assisted confirmation of multi-pesticide residue in dried tangerine peel†
A sorbent package consisting of a combination of multiwalled carbon nanotubes (MWNTs) and a primary secondary amine (PSA) has been used for a modified quick, easy, effective, rugged, and safe (QuEChERS) extraction of 104 pesticides from dried tangerine peel samples. MWNTs and graphitized carbon black (GCB) have been compared in terms of purification efficiency and recovery; the best results were achieved with MWNTs. The pesticides were quantified on a liquid chromatography tandem mass spectrometry (LC-MS/MS) system in scheduled multiple reaction monitoring mode, and identified on the basis of product ion abundance ratios as well as characteristic fragments in enhanced product ion spectra. Calibration curves for most of the analytes showed correlation coefficients better than 0.9916. Detection limits ranged from 0.2 to 40 μg kg−1. Good precision was achieved with relative standard deviations of less than 20%. Results of accuracy in spiked samples were in the range 71.1–117.6%, except for pesticides such as thiabendazole, teflubenzuron, hexaflumuron, and methomyl. The proposed method has been applied to 57 dried tangerine peel samples from the Chinese market; 16 pesticides were detected, including carbendazim, chlorpyrifos, isoprothiolane and methidathion, at levels that exceeded the recommended maximum residue limits in some samples. The newly established method has advantages of good recovery and a rapid clean-up procedure, showing enhanced product ion scan-assisted confirmation to be a useful tool for obtaining reliable results.