Quasi-molecular ion

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Quasi-molecular ion
This term is deprecated.
Related Term(s): protonated molecule
From Definitions of Terms Relating to Mass Spectrometry (IUPAC Recommendations 2013); DOI: 10.1351/PAC-REC-06-04-06 © IUPAC 2013.

Index of Recommended Terms


Gold Book


IUPAC. Compendium of Chemical Terminology, 2nd ed. (the Gold Book). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997).

Quasi-molecular ion


A protonated molecule or an ion formed from a molecular ion by loss of a hydrogen atom. The use of the term 'pseudo-molecular ion' is not recommended.

Source: PAC, 1991, 63, 1541 (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1550

IUPAC Gold Book
Index of Gold Book Terms

Orange Book


IUPAC. Analytical Division. Compendium of Analytical Nomenclature (the Orange Book). Definitive Rules, 1979.

Quasi-molecular ion

A term used to represent a protonated molecule or an ion formed from a molecular ion by loss of a hydrogen atom.

IUPAC 1997 Orange Book Chapter 12
Index of Orange Book Terms

External links

http://dx.doi.org/10.1002/jms.4700 "The term quasimolecular ion has been used to describe ions comprising a molecule and weakly bound positive or negative ion or an ion formed by the loss of a proton from a molecule. This term was used in mass spectrometry from the late 1960s after the development of chemical ionization but has been deprecated in recent terms recommendations due to what is perceived as its overly broad use. This letter argues that the term is well-defined and has a long history of use in mass spectrometry and other fields and should be considered as a recommended term."