Editing Electron ionization (section)

==== Environmental analysis ====
GC-EI-MS has been successfully used for the determination of pesticide residues in fresh food by a single injection analysis. In this analysis 81 multi-class [[pesticide]] residues were identified in vegetables. For this study the pesticides were extracted with [[dichloromethane]] and further analyzed using gas chromatography–[[tandem mass spectrometry]] (GC–MS–MS). The optimum ionization method can be identified as EI or [[chemical ionization]] (CI) for this single injection of the extract. This method is fast, simple and cost effective since high numbers of pesticides can be determined by GC with a single injection, considerably reducing the total time for the analysis.<ref>{{Cite journal|last1=Arrebola|first1=F. J.|last2=Martı́nez Vidal|first2=J. L.|last3=Mateu-Sánchez|first3=M.|last4=Álvarez-Castellón|first4=F. J.|date=2003-05-19|title=Determination of 81 multiclass pesticides in fresh foodstuffs by a single injection analysis using gas chromatography–chemical ionization and electron ionization tandem mass spectrometry|journal=Analytica Chimica Acta|volume=484|issue=2|pages=167–180|doi=10.1016/S0003-2670(03)00332-5|bibcode=2003AcAC..484..167A }}</ref>