Determination of pesticide residues in tobacco by gas chromatography. negative chemical ionization/electron impact ionization. time of flight mass spectrometry coupled with microwave assisted extraction

A method was developed for the analysis of 24 pesticide residues in tobacco based on gas chromatography. time of flight mass spectrometry (GC-TOF MS) under negative chemical ionization (NCI) and electron impact ionization (EI) modes coupled with microwave-assisted extraction. The tobacco samples were extracted with 10 mL dichloromethane-n-hexane (3 : 1, v/v) for 10 min at 100 degrees C by microwave-assisted extraction, and cleaned up by a florisil solid phase extraction cartridge, then detected by GC-TOF MS. For GC-NCI-TOF MS and GC-EI-TOF MS, the linear correlation coefficients (r(2)) were both better than 0.99, the relative standard deviations (RSD) were less than 8.6% and 9.1%, the limits of quantification ranged from 0.3 mu g/kg to 6.9 mu g/kg and 10.2 mu g/kg to 44.9 mu g/kg, and the recoveries ranged from 75.2% to 94.8% and 75.0% to 95.1% at three spiked levels, respectively. Comparison of the total ion chromatograms and mass spectra under NCI and EI modes, the NCI modes have the advantages of higher selectivity with better matrix interference resistance and simpler spectrogram. The detection limits in NCI mode were lower by more than one order of magnitude than those in EI mode, GC-NCI-TOF MS method was superior in analyzing low level of pesticide residues and complex matrix.