Talk:Thomson (unit)

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[edit] 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 It is a letter not an article (i.e. not peer reviewed).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)