Editing Electron ionization (section)

=== Ion trap mass spectrometry ===
Ion trap EI MS can be incorporated for the identification and quantitation of nonylphenol polyethoxylate (NPEO) residues and their degradation products such as nonylphenol polyethoxy carboxylates and carboxyalkylphenol ethoxy carboxylates, in the samples of river water and sewage effluent. Form this research, they have found out that the ion trap GC- MS is a reliable and convenient analytical approach with variety of ionization methods including EI, for the determination of target compounds in environmental samples.<ref>{{Cite journal|last1=Ding|first1=Wang-Hsien|last2=Tzing|first2=Shin-Haw|date=1998-10-16|title=Analysis of nonylphenol polyethoxylates and their degradation products in river water and sewage effluent by gas chromatography–ion trap (tandem) mass spectrometry with electron impact and chemical ionization|journal=Journal of Chromatography A|volume=824|issue=1|pages=79–90|doi=10.1016/S0021-9673(98)00593-7|pmid=9818430}}</ref>