Talk:Thomson (unit)

References

For anybody out there who can actually dig up a real reference for this article, can you correct the references section? Brian Jason Drake 03:44, 9 June 2006 (UTC)

The reference is: Cooks, R. G. and A. L. Rockwood (1991). "The 'Thomson'. A suggested unit for mass spectroscopists." Rapid Communications in Mass Spectrometry 5(2): 93.

Online copy at [1] of course you must have access. It is a letter not an article (i.e. not peer reviewed). Here is selected quote of the most relevant portion:

"Second, that a unit of mass-to-charge ratio be adopted. After all, this is the quantity which all mass spectrometers measure; mass is a derived quantity requiring an independent measurement or knowledge of charge. Such a unit would be defined as the quotient of mass, in units of u* and the number of charges, z. The number of charges could be positive or negative, depending on the sign of the charge. The name Thomson suggests itself in view of J. J. Thomson’s contributions to measurement of this quantity and his preeminent role in the evolution of mass spectrometry. Using standard rules for abbreviation, we have 1 Th = 1 u/ atomic charge. For example, the molecular weight of the peptide myoglobin (isotopic average molecular weight 16950~) can be deduced from measurement3 of a peak at 998.O Th, provided it is known that the ion bears 17 charges. If this suggestion is accepted, other simplifications ensue. For example, the benzoate anion, mass 121 u and charge -1 atomic units, is -121 Thomson not m/z121. The latter is actually the mass-to-charge ratio of the corresponding (unstable) cation!"

No where in the article does it even mention m/q. Note that the other references given in this wikipedia article use m/z. See also The mass spectrometry wiki version of this article--Nick Y. 22:05, 21 July 2006 (UTC)

The important section of above article is: ... that a unit of mass-to-charge ratio be adopted. This clearly states that the thomson was meant to be a unit for mass-to-charge ratio. Many people incorrectly think that m/z is a symbol to express the mass-to-charge ratio. This, however is not true, since m/z is a dimensionless property and mass-to-charge ratio has the dimension mass/charge, as its name suggests. In other words: many people use m/z (the symbol for a physiscal property) in combination with the unit thomson because they are not aware that m/z is officially not a mass-to-charge ratio. When m/z is used according to the rules of IUPAC orange book then it is dimensionless and therefore, per definition, does not have any units.

Kehrli 16:14, 22 July 2006 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as stub, and the rating on other projects was brought up to Stub class. BetacommandBot 10:04, 10 November 2007 (UTC)

Article in Japanese

Anyone read Japanese? Only the abstract of this article is in English: "Comments on Abscissa Labeling of Mass Spectra". Journal of the Mass Spectrometry Society of Japan. 55 (1): 51–61. 2007. Retrieved 2007-12-05. {{cite journal}}: Cite has empty unknown parameter: |coauthors= (help) --Kkmurray (talk) 23:48, 5 December 2007 (UTC)

I was told by someone who reads Japanese that this editorial is supportive of the thomson unit, so I added the ref and some words to that effect to the article. --Kkmurray (talk) 15:59, 7 December 2007 (UTC)

Update

I updated the article and added some refs. Note that Rockwood specifically defines the unit in terms of z, not e as in the previous version of the article. --Kkmurray (talk) 04:08, 7 December 2007 (UTC)

POV and OR

I removed some POV and OR that had crept back into the article. --Kkmurray (talk) 23:42, 18 November 2010 (UTC)

More cleanup

It said, “For example, for the ion C₇H₇²⁺ has an exact mass of 91.0 Da.” I rewrote it as, “For example, the ion C₇H₇²⁺ has a mass of 91 Da.” 91.0 Da isn’t exact; atomic masses aren’t exact multiples of a dalton, the ion has lost two electron-masses, and there is a possibility of the ion being heavier than usual due to a deuterium or carbon-13. Okay?--Solomonfromfinland (talk) 22:20, 23 November 2014 (UTC)

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it seems to be all wrong

thomson cannot be a unit for m/z or so-called mass-to-charge ratio (relative molecular mass to charge number), as (not only) according to IUPAC, m/z is a dimensionless quantity, thus thompson [Th] per se also needs to be dimensionless unit. the whole confusion comes from rather misleading use of dalton [Da] as a synonym for atomic mass constant u and thus misinterpreting the relative molecular mass (m in the m/z term) with the molecular mass with u or Da as unit (M_r(¹²C) = 12 ~ m(¹²C) = 12 u or Da). followingly, next problem is a labslang use of the word charge, where we should use scientifically correct charge number. voilà, and here we are. in my professional opinion as a mass spectrometrist, Da and Th are just psychological issues (our brain likes to say "how much of what", not just plain numeral, it is more pleasing to say mass of 125 thompson than em-over-zet 125) rather than necessary units. Regis (talk) 11:55, 22 August 2018 (UTC)

You are right. It is all wrong. The underlying problem is that the definition of m/z as a "unitless" quantity is nonsensical at the outset. It makes no more sense to define m/z as unitless than it does to define the meter or the kilogram or one meter per second as unitless quantities. Mass is not a unitless quantity and charge is not a unitless quantity, so it makes no sense to define the mass to charge ratio as a unitless quantity. Therefore, to the extent that m/z is considered unitless it makes no sense to refer to it as a mass to charge ratio. In that sense any attempt to put m/z on a solid metrological footing is doomed to failure as long as it continues to be considered a unitless number. This creates a terrible mess of the terminology of mass spectrometry that would not pass muster in an introductory chemistry class.

To give one small example of the problems of a unitless m/z, one cannot substitute it into the equations of motion of an ion in an electrostatic or magnetic field and have the units come out correct in the answer.

A simple solution to this would be to re-define m/z as a number that has units, and specify the units to be unified atomic mass units per elementary charge. It also makes sense to give it a name, such as "Thomson" because "unified atomic mass units per elementary charge" is too much of a mouthful and therefore awkward to say or write.

A quick note on the proper way to report a measurement. A proper measurement consists of several parts. including 1) What type of quantity is being measured (mass, velocity, mass-to-charge ratio, etc.) 2) Specifically what is being measured (e.g. the mass of an individual named "Robert", the mass-to-charge ratio of the CO+ ion, etc.) 3) A number 4) Units

For example, one could say "The mass of Robert is 77 kg". Here we have the type of quantity being measured (mass), specifically what the measurement is being applied to (Robert), a numerical value (77), and the units of the measurement (kg). Any measurement that does not contain these four elements is not a scientifically correct measurement. For example, one could not say "The mass of Robert is 77." Unfortunately, the way mass spectrometrists report m/z does not conform to these rules and is therefore nonsense from a metrological point of view.

The paper by Cooks and Rockwood attempts to correct this, along with giving a convenient name to the mass to charge ratio on the atomic/molecular scale. Unfortunately, the mass spectrometry community seems to not care about these matters and refuses to use terminology that is metrologically correct and consistent. Massmanute (talk) 23:08, 11 December 2018 (UTC)