title: [Determination of acetanilide herbicide residues in tea by gas chromatography-mass spectrometry with two different ionization techniques].
abstract: An analytical method of solid phase extraction-gas chromatography-mass spectrometry with two different ionization techniques was established for simultaneous determination of 12 acetanilide herbicide residues in tea-leaves. Herbicides were extracted from tea-leaf samples with ethyl acetate. The extract was cleaned-up on an active carbon SPE column connected to a Florisil SPE column. Analytical screening was determined by the technique of gas chromatography (GC)-mass spectrometry (MS) in the selected ion monitoring (SIM) mode with either electron impact ionization (EI) or negative chemical ionization (NCI). It is reliable and stable that the recoveries of all herbicides were in the range from 50% to 110% at three spiked levels, 10 microg/kg, 20 microg/kg and 40 microg/kg, and the relative standard deviations (RSDs) were no more than 10.9%. The two different ionization techniques are complementary as more ion fragmentation information can be obtained from the EI mode while more molecular ion information from the NCI mode. By comparison of the two techniques, the selectivity of NCI-SIM was much better than that of EI-SIM method. The sensitivities of the both techniques were high, the limit of quantitative (LOQ) for each herbicide was no more than 2.0 microg/kg, and the limit of detection (LOD) with NCI-SIM technique was much lower than that of EI-SIM when analyzing herbicides with several halogen atoms in the molecule.
authors.affiliation: Laboratory of Food, Jiangsu Entry-Exit Inspection and Quarantine Bureau, Nanjing 210001, China. swj9722418@yahoo.com.cn
authors.forename: Weijian
authors.initials: W
authors.lastname: Shen
authors.forename: Jinzhong
authors.initials: J
authors.lastname: Xu
authors.forename: Wenquan
authors.initials: W
authors.lastname: Yang
authors.forename: Chongyu
authors.initials: C
authors.lastname: Shen
authors.forename: Zengyun
authors.initials: Z
authors.lastname: Zhao
authors.forename: Tao
authors.initials: T
authors.lastname: Ding
authors.forename: Bin
authors.initials: B
authors.lastname: Wu
mesh_terms: D000083:Acetanilides / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006540:Herbicides / Q000032:analysis*; D057230:Limit of Detection; D013662:Tea / Q000737:chemistry*
chemical_list: D000083:Acetanilides; D006540:Herbicides; D013662:Tea; C508827:acetanilide