Editing Electron ionization (section)

==== Analysis of biological fluids ====
The GC-EI-MS can be incorporated for the analysis of biological fluids for several applications. One example is the determination of thirteen synthetic [[pyrethroid]] [[insecticide]] molecules and their [[Stereoisomerism|stereoisomers]] in whole blood. This investigation used a new rapid and sensitive electron ionization-gas chromatography–mass spectrometry method in [[Gas chromatography–mass spectrometry|selective ion monitoring]] mode (SIM) with a single injection of the sample. All the pyrethroid residues were separated by using a GC-MS operated in electron ionization mode and quantified in selective ion monitoring mode. The detection of specific residues in blood is a difficult task due to their very low concentration since as soon as they enter the body most of the chemicals may get excreted. However, this method detected the residues of different pyrethroids down to the level 0.05–2&nbsp;ng/ml. The detection of this insecticide in blood is very important since an ultra-small quantity in the body is enough to be harmful to human health, especially in children. This method is a very simple, rapid technique and therefore can be adopted without any matrix interferences. The selective ion monitoring mode provides detection sensitivity up to 0.05&nbsp;ng/ml.<ref>{{Cite journal|last1=Ramesh|first1=Atmakuru|last2=Ravi|first2=Perumal Elumalai|date=2004-04-05|title=Electron ionization gas chromatography–mass spectrometric determination of residues of thirteen pyrethroid insecticides in whole blood|journal=Journal of Chromatography B|volume=802|issue=2|pages=371–376|doi=10.1016/j.jchromb.2003.12.016|pmid=15018801}}</ref> Another application is in [[protein turnover]] studies using GC-EI-MS. This measures very low levels of [[Phenylalanine|d-phenylalanine]] which can indicate the enrichment of [[amino acid]] incorporated into tissue protein during studies of human protein synthesis. This method is very efficient since both free and protein-bound d-phenylalanine can be measured using the same mass spectrometer and only a small amount of protein is needed (about 1&nbsp;mg).<ref>{{Cite journal|last1=Calder|first1=A. G.|last2=Anderson|first2=S. E.|last3=Grant|first3=I.|last4=McNurlan|first4=M. A.|last5=Garlick|first5=P. J.|date=1992-07-01|title=The determination of low d5-phenylalanine enrichment (0.002–0.09 atom percent excess), after conversion to phenylethylamine, in relation to protein turnover studies by gass chromatography/electron ionization mass spectrometry|journal=Rapid Communications in Mass Spectrometry|language=en|volume=6|issue=7|pages=421–424|doi=10.1002/rcm.1290060704|pmid=1638043|issn=1097-0231|bibcode=1992RCMS....6..421C}}</ref>