...is a soft ionization method used for the detection of quasimolecular ions, hence one can calculate a molecular formula. Another useful approach is to study gas phase reactions or apply CI for structure elucidation purposes. See some interesting books. A CrossRef search on Chemical Ionization Mass spectrometry [Long] [Short].
One general problem with CI is the generally lower intensity of peaks observed compared to EI. Another problem is that no large spectral library exist (as the NIST DB for EI spectra) which makes identification a very unpleasant experience. But with tuning one can generate mixed spectra which contain EI and CI data, that can be (somehow) search in EI libraries. Only few labs use chemical ionization which was very popular in 1980s but there is a growing trend in CI because of sensitivity for certain chemicals in negative mode and of course the molecular ion detection.
There are several neat tricks which show the importance of chemical ionization for gas chromatography based structure elucidation. We outlined them in several talks using our Seven Golden Rules concept. As the detection of the molecular ion is the general enabler for all following interpretations and predictions (including substructures, retention indices) soft ionization techniques are of extremely importance. See my COSMOS slides [PDF].
Since large molecule databases are available (KEGG, PubChem, ChemSpider) it is also possible to download such molecules and perform molecular calculations which could help the chemical ionization structure elucidation process. One example is the prediction of proton affinities. One could for instance calculate what kine of molecular ion for certain substance classes can be expected (in case of CH4 as reaction gas a [M-H]+ will be observed in positive CI ionization for alkanes). Other approaches would be the prediction of other observed adducts.
So every metabolomics lab which is not only performing GC-MS based metabolite profiling, but is also is interested in discovery processes, should have at least one accurate mass, accurate isotopic abundance, fast scanning (10-20 spectra per second or better) chemical ionization mass spectrometer available.
Title | Construction and Use of a Versatile Chemical Ionization Manifold |
Source | James L. Little; Eastman Chemical Company users.charter.net/slittle/ |
DOI | - |
Short Review |
This script describes the installation of a manifold for 15 different gases for chemical ionization (CI). Volatile liquids (methanol, acetone) and deuterium labeled gases can be used. |
Title | Chemical Ionization |
Source | Mass Spectrometry - A Textbook Jürgen H. Gross www.ms-textbook.com/downloads/chap7.pdf |
DOI | 3-540-40739-1 |
Short Review |
This chapter from Mass Spectrometry - A Textbook by Jürgen H. Gross gives a short and comprehensive overview about chemical ionization for mass spectrometry. Gas phase chemistry topics are discussed and several examples and illustration round up this chapter. |
Title | Chapter 7 Chemical Ionization |
Source | Introduction to Mass Spectrometry, Fourth Edition (Fourth Edition) J. Throck Watson, O. David Sparkman |
DOI | dx.doi.org/10.1002/9780470516898.ch7 |
Short Review |
That chapter discusses many important aspects (proton affinities, gas-phase basicities, fragmentations) of chemical ionization. Several examples show the utility for pesticide and metabolite analysis. General fragmentation rules and many practical considerations make that chapter a very important read to generally understand CI. |
Title | |
Source | |
DOI | dx.doi.org/ |
Short Review |
Title | |
Source | |
DOI | dx.doi.org/ |
Short Review |