Editing Chemical ionization (section)

{{Short description|Technique in mass spectroscopy}}
{{Use American English|date = February 2019}}
[[File:Chemical Ionization.png|thumb|A schematic diagram of chemical ionization source]]
'''Chemical ionization''' ('''CI''') is a [[ionization|soft ionization]] technique used in [[mass spectrometry]].<ref name="pmid4569234">{{cite journal |vauthors=Fales HM, Milne GW, Pisano JJ, Brewer HB, Blum MS, MacConnell JG, Brand J, Law N |title=Biological applications of electron ionization and chemical ionization mass spectrometry |journal=Recent Prog. Horm. Res. |volume=28 |pages=591–626 |year=1972 |pmid=4569234 }}</ref><ref name=":5">{{Cite journal|last=Field|first=Frank H.|title=Chemical ionization mass spectrometry|journal=Accounts of Chemical Research|language=en|volume=1|issue=2|pages=42–49|doi=10.1021/ar50002a002|year=2002}}</ref> This was first introduced by Burnaby Munson and [[Frank H. Field]] in 1966.<ref name=":2">{{cite book|author=Alex. G. Harrison|title=Chemical Ionization Mass Spectrometry, Second Edition|url=https://books.google.com/books?id=HJ-j71b7yfIC&pg=PA1|date=15 June 1992|publisher=CRC Press|isbn=978-0-8493-4254-7|pages=1–}}</ref> This technique is a branch of gaseous ion-molecule chemistry.<ref name=":5" /> Reagent gas molecules (often methane or ammonia)<ref>{{Cite web |title=Mass Spectrometry Facility {{!}} CI |url=http://www.chm.bris.ac.uk/ms/ci-ionisation.xhtml |access-date=2022-04-30 |website=www.chm.bris.ac.uk |language=en}}</ref> are ionized by [[electron ionization]] to form reagent ions, which subsequently react with analyte molecules in the gas phase to create analyte ions for analysis by mass spectrometry. Negative chemical ionization (NCI), charge-exchange chemical ionization, [[atmospheric-pressure chemical ionization]] (APCI) and [[atmospheric pressure photoionization]] (APPI) are some of the common variants of the technique. CI mass spectrometry finds general application in the identification, [[structure elucidation]] and [[quantitation]] of organic compounds<ref name=":0">{{cite journal|last1=Hunt|first1=Donald F.|last2=McEwen|first2=Charles N.|last3=Harvey|first3=T. Michael.|title=Positive and negative chemical ionization mass spectrometry using a Townsend discharge ion source|journal=Analytical Chemistry|volume=47|issue=11|pages=1730–1734|doi=10.1021/ac60361a011|language=en|year=2002}}</ref> as well as some utility in biochemical analysis.<ref name=":0" /> Samples to be analyzed must be in vapour form, or else (in the case of liquids or solids), must be vapourized before introduction into the source.