Thomson (unit)
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The unit Thomson is a unit that has appeared infrequently in scientific literature relating to the field of mass spectrometry as a unit of m/z. It was never widely used and is not accepted by most journals in the field. It has also been proposed within IUPAC that the unit be specifically rejected and deprecated after years of simply not being accepted by IUPAC or any other standards body.
Cooks and Rockwood proposed the unit thomson (Th) for the physical quantity mass-to-charge ratio defined by:
- 1 Th == 1 u/e == 1 Da/e.
where u represents the atomic mass unit, Da represents the unit dalton, and e represents the atomic charge unit.
For example, for the ion C7H72+ an ion will be observed at 45.5 m/z Th
An interesting part of their proposal allowed for negative values for negatively charged ions. The name refers to Joseph John Thomson who measured the mass-to-charge ratio of electrons and ions. The thomson is not a SI unit, nor is it currently accepted by IUPAC. The thomson complies better to the international standards about quantities and units as described in ISO 31 and the IUPAC green book than the unitless m/z that is almost universally used for labeling mass spectra.
Today, the thomson is used by some authors of scientific posters and papers, as can be seen in the following examples:
[edit] References
- Cooks, R. G. and A. L. Rockwood (1991). "The 'Thomson'. A suggested unit for mass spectroscopists." Rapid Communications in Mass Spectrometry 5(2): 93.
