M/z

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IUPAC RECOMMENDATIONS 2013

K. K. Murray, R. K. Boyd, M. N. Eberlin, G. J. Langley, L. Li and Y. Naito, Pure Appl. Chem., 2013, 85, 1515-1609, 10.1351/PAC-REC-06-04-06.

M/z
m/z

Deprecated: mass-to-charge ratio, Thomson.

Abbreviation representing the dimensionless quantity formed by dividing the ratio of the mass of an ion to the unified atomic mass unit, by its charge number (regardless of sign). The abbreviation is written in italicized lowercase letters with no spaces.

Note 1: Mass-to-charge ratio is deprecated. Mass-to-charge ratio has been used occasionally for the horizontal axis in a plot of a mass spectrum, although the quantity measured is not the ion’s mass divided by its electric charge (SI units kg C–1). However, m/z is recommended as an abbreviation to represent the dimensionless quantity that is used almost universally as the independent variable in a mass spectrum.
Note 2: The abbreviation m/z should not be used as a variable in a mathematical equation. Instead, the variables m (in kg) and q (in C) should be used to denote mass and charge.
Note 3: The equal sign should not be used to denote a m/z value, for example, use m/z 100 and not m/z = 100.
Note 4: The thomson (Th) unit is deprecated.
Related Term(s):
Reference(s):

IUPAC. Analytical Division. Compendium of Analytical Nomenclature (the “Orange Book”). Definitive Rules, 1979. Compiled by J. Inczédy, T. Lengyel, A. M. Ure. Blackwell Scientific Publications, Oxford (1997). On-line corrected version: http://www.iupac.org /publications/analytical compendium (2000).

IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins.

Definitions of Terms Relating to Mass Spectrometry (IUPAC Recommendations 2013); DOI: 10.1351/PAC-REC-06-04-06 © IUPAC 2013.


Index of Terms

 




Orange Book

ORANGE BOOK DEFINITION

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

M/z

m/z ratio.

IUPAC Orange Book Chapter 12
Index of Orange Book Terms


Gold Book

GOLD BOOK DEFINITION

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

M/z

The abbreviation m/z is used to denote the dimensionless quantity formed by dividing the mass number of an ion by its charge number. It has long been called the mass-to-charge ratio although m is not the ionic mass nor is z a multiple or the elementary (electronic) charge, e. The abbreviation m/e is, therefore, not recommended. Thus, for example, for the ion C7H72+, m/z equals 45.5.

IUPAC Gold Book
Index of Gold Book Terms


m/z issues

QUOTED TEXT FROM IUPAC RECOMMENDATIONS 2013
The labeling of the x-axis of a mass spectrum engendered the most discussion during the creation of this document; however, in spite of a general desire for a better way to label the x-axis of mass spectra, there was no broad consensus for any of the proposed changes. Therefore, this document continues the use of the definitions of the Gold Book [1] and the similar definitions in the Orange Book [2]. The Gold Book recommendation is for the use of m/z as an abbreviation for mass-to-charge ratio, a dimension- less quantity obtained by dividing the mass number of an ion by its charge number [3].

The thomson unit, defined as the quotient of mass in units of u and the number of charges (z), was proposed nearly two decades ago [4], but has not been widely adopted and is therefore not recommended. Labeling the x-axis of a mass spectrum with any unit of mass such as dalton (Da), atomic mass unit (amu), or unified atomic mass unit (u) is strongly discouraged due to the confusion that would result when reporting spectra of multiply charged ions. The quantity plotted on the x-axis of a mass spectrum is a function of both the mass and charge of the ion. Furthermore, the use of amu in place of u is strongly discouraged in all cases; it has been used to denote atomic masses measured relative to the mass of a single atom of 16O, or to the isotope-averaged mass of an oxygen atom, or to the mass of a single atom of 12C

From Definitions of Terms Relating to Mass Spectrometry (IUPAC Recommendations 2013); DOI: 10.1351/PAC-REC-06-04-06 © IUPAC 2013.


External links

WIKIPEDIA ARTICLE
This term has a corresponding Wikipedia article: M/z