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{{DefName|The symbol ''m/z'' is used to denote the dimensionless quantity formed by dividing the mass number of an ion by its charge number. The symbol should consist of italicized lower case letters with no spaces.}}
{{Final
|acronym=
|def='''m/z'''
Deprecated: [[mass-to-charge ratio]], [[Thomson]].


{{Disc}}
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<sup>-1</sup>). 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'' &#61; 100.
:''Note 4'': The [[thomson]] (Th) unit is deprecated.
|rel=
|ref={{obgb}}
}}


<!-- Orange Book -->
{{orange|
''m/z'' ratio.
}}


== [[Orange Book]] Entry ==
<!-- Gold Book -->
{{gold|
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 C<sub>7</sub>H<sub>7</sub><sup>2+</sup>, ''m/z'' equals 45.5.
}}


''[[m/z]]'' ratio.


== [[Gold Book]] Entry ==
{{Moverz controversy}}


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 C<sub>7</sub>H<sub>7</sub><sup>2+</sup>, ''[[m/z]]'' equals 45.5.


==Wikipedia==
{{wplink}}


== Related Terms ==
==Bibliography==
 
*R.G. Cooks, A.L. Rockwood, The Thomson - A Suggested Unit For Mass Spectroscopists, 5 (1991) 93–93. {{doi}}10.1002/rcm.1290050210
[[Mass/Charge Ratio]]
*K. L. Busch, "Units in Mass Spectrometry" ''Spectroscopy'', '''16''', 28, (2001)[https://www2.chemistry.msu.edu/courses/cem832/units_of_mass.pdf]
 
*健. 吉野, 目から鱗のマススペクトロメトリー第7回「マススペクトルの横軸項目表記法」~Daは分子量の単位ではありません~ TI , ''Journal of the Mass Spectrometry Society of Japan''. '''55''' (2007) 51–62.{{doi}}10.5702/massspec.55.51
[[Thomson]]
*健. 吉野, 目から鱗のマススペクトロメトリー<br>第15回「<i>m</i>/<i>z</i> の単位?」<br>&sim;「マス」って何の単位ですか?&sim; TI , ''Journal of the Mass Spectrometry Society of Japan''. '''56''' (2008) 241–245.{{doi}}10.5702/massspec.56.241
 
[[Dalton]]
 


[[Category:Mass]]
[[Category:Mass]]
 
[[Category:acronym]]
[[Category:Units]]
[[Category:Units]]
{{DEFAULTSORT:MZ}}

Revision as of 18:28, 3 August 2019

IUPAC RECOMMENDATIONS 2013
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.

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

 




Orange Book

ORANGE BOOK DEFINITION

IUPAC. Analytical Division. Compendium of Analytical Nomenclature (the Orange Book). Definitive Rules, 1979 (see also Orange Book 2023)

M/z

m/z ratio.

IUPAC 1997 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



Past definitions and discussion regarding m/z

The 2013 IUPAC recommendations retain the use of m/z as the x-axis of a mass spectrum which has been in place since the early 1970s (see ASMS 1974 and Beynon 1978). Note that m is taken as the mass in u (per Price 1991; McLafferty 1993) rather than mass number (per Todd 1991; Todd 1995).

2013 IUPAC Comment

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.

ASMS 1997 Terms and Definitions Poster

The ASMS 1997 definition is similar to the McLafferty 1993 definition.

Mass-to-charge ratio (m/z)
Daltons/electronic charge.
Note from a reader: on Thomson - the fluid dynamics people have already used that one; it is listed in the CRC Handbook and IUPAC documents. ASMS should be doing things in addition to or clarifying points mentioned (or not) in IUPAC. However, we should be cautious about doing anything that actually opposes or conflicts with IUPAC documents.

Gold Book

The IUPAC Gold Book uses the mass number definition of Todd 1991. The IUPAC Orange Book definition is simply "m/z ratio".

http://goldbook.iupac.org/M03752.html

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..

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 1544

Todd 1995; Todd 1991

Todd uses the mass number definition of Beynon 1978.

m/z
This abbreviation 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 of the elementary (electronic) charge, e. The abbreviation m/e is, therefore, not recommended. Thus, for example, for the ion C7H72+, m/z = 45.5.

. . .

The number of charges carried by an ion should be indicated by the symbol z. The ratio of the mass number of an ion to the number of charges carried (commonly referred to as the mass-to-charge ratio) should be written m1/z, m2/z, etc. m/e should not be used to indicate this ratio, e (italic) being reserved for the charge upon the electron and e (Roman) for the electron itself when it appears in an equation.

McLafferty 1993

McLafferty uses mass rather than mass number and notes the proposed thomson unit (see ASMS 1991).

m/z
The mass of the ion in daltons divided by its charge (usually unity), a Thomson; m/e has also been used.

Price 1991

Price 1991 definition uses mass rather than mass number usage.

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

ASMS 1981

The 1981 ASMS meeting continues the mass number usage. ASMS Nomenclature Committee Workshops, Minneapolis, 1981 [5]

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

Beynon 1978

Beynon 1978 is the first published recommendation for m/z as opposed to m/e.

An acronym, abbreviation or invented jargon should only be used after a full explanation of its meaning has been given in the text.

. . .

The only exceptions, relating to mass spectroscopy, should be the following few commonly accepted initials that may be used freely and without amplification:

. . .

m/z meaning mass-to-charge ratio

. . .

The number of charges carried by an ion should be indicated by the symbol z. The ratio of the mass number of an ion to the number of charges carried (commonly referred to as the mass-to-charge ratio) should be written m1/z, m2/z, etc. m/e should not be used to indicate this ratio, e being reserved for the charge upon the electron and e- for the electron itself when it appears in an equation.

ASMS 1974

The 1974 ASMS meeting marks the m/e to m/z changeover.

Progress Report from ATSM Committee E-14 Subcommittee 10, presented at the Twenty-Second Annual Conference on Mass Spectrometry and Allied Topics, Philadelphia, Pennsylvania, May 19-24, 1974. pp. 545-561 [6]

. . .

Mass, mass-to-charge ratio, m/e, etc.

The major problem here, which has troubled many workers, lies in the symbol "m/e." As one of our group has stated the matter, in most of chemistry and physics, "m" means the mass in grams and "e" is the charge on the electron (or the electron itself when it is part of an equation). The use of 'M' for molecular mass in atomic mass units and that of "z" for the number of charges on an ion are established and unambiguous in physics and chcmistry(1,2). Thus, "M/z" would appear to be the preferred notation.

A minor problem centers about the term used to denote this same quantity. Not too many years back, the established term was "specific mass"(3), which perhaps merits revival. Such revival would not be in accord with the lUPAC recommended usage of the word "specific," preceding the name of an extensive physical quantity, to mean "divided by mass"(4). On the other hand, it would not be the only exception to this recommendation. For example, "specific ionization" is a well established term denoting the number of ion pairs produced per unit of distance along the track of an ionizing particle(5,6).

Incidentally, the lUPAC-recommended symbol for atomic mass units is "u" rather than "amu"(4).


1.1. Since m/e is such a well-established term, I think it should not be abandoned, especially since the meaning of m and e in this context is clear, After all, m has quite a number of meanings. M/z would apply only to M+ what about the other "m/e" values?


1.II. M/z is acceptable.


1.III. Very good. I agree that specific mass might well be an acceptable method of expressing mass to charge ratio.


1.IV. "z" would appear to be preferable to e as the number of charges on the ion but if M is used for the mass of any ion (as is done in the A.V.S. Standard)(7) it will conflict with the definition of M for the molecular ion. One could, of course, call the molecular ion P (molecular parent ion or primary ionised species) but the use of M is well established. If M is the molecular ion we must use m/z for the mass to charge ratio of ions other than M and ignore the fact that m is usually mass in grams. I do not like referring to an ion of mass m but can see no way out of it other than using M*, M[bar] or some other horrible device for the molecular ion. M is already used for the apparent mass of a metastable ion and M signifies an average). Mass units should be in line with IUPAC using "u", i.e. the loss of 28 u.


1.V. In order to say what we mean and have general scientific understanding, I favor "M/z" for mass-to-charge ratio and "µ" for atomic mass unit.


1.VII. 'M/z' indeed appears to be the preferred notation. It would not lead to great difficulties for those familiar with the symbol m/e. For atomic mass units 'u' is also preferable. To denote M/z, the term "specific mass", although not recommended by the IUPAC, is still better than "mass over charge" or "mass-charge ratio".


1.IX.

I whole-heartedly approve of the notation M/Z for mass-to-charge ratio. However, with respect to the term "specific mass", I cannot show any enthusiasm. I feel that the additional length of the term "mass-to-charge ratio" is worthwhile inasmuch as there is now a distinct difference between it and mass. The most important thing in this regard is for journals and referees to insist on mass-to-charge ratio for mass spectral scales and mass for whenever they mean mass. The term "specific mass" will probably be subjected to the same sloppy writing habits as its predecessor, but will not have any of the advantages in clarity.


Wikipedia

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

Bibliography

  • R.G. Cooks, A.L. Rockwood, The Thomson - A Suggested Unit For Mass Spectroscopists, 5 (1991) 93–93. http://dx.doi.org/10.1002/rcm.1290050210
  • K. L. Busch, "Units in Mass Spectrometry" Spectroscopy, 16, 28, (2001)[7]
  • 健. 吉野, 目から鱗のマススペクトロメトリー第7回「マススペクトルの横軸項目表記法」~Daは分子量の単位ではありません~ TI , Journal of the Mass Spectrometry Society of Japan. 55 (2007) 51–62.http://dx.doi.org/10.5702/massspec.55.51
  • 健. 吉野, 目から鱗のマススペクトロメトリー
    第15回「m/z の単位?」
    ∼「マス」って何の単位ですか?∼ TI , Journal of the Mass Spectrometry Society of Japan. 56 (2008) 241–245.http://dx.doi.org/10.5702/massspec.56.241