Cooks and Rockwood proposed the unit thomson (Th) for the phyiscal quantity mass-to-charge ratio: Sir Joseph John Thomson Sir Joseph John Thomson (18 December 1856 – 30 August 1940), often known as J. J. Thomson, was an English physicist, the discoverer of the electron. ... For usage in mass spectrometry see mass spectrum. ...

The thomson is 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⁺, m/q = 45.5 Th or m/q = 45.5 Da/e.

The name refers to Joseph John Thomson who measured the mass-to-charge ratio m/Q of electrons and ions. The thomson has the symbol Th and is used by some scientists in mass spectrometry. The thomson is not a SI unit, nor is it currently accepted by IUPAC. However, the thomson complies better to the international standards about quantities and units as described in ISO 31 and the IUPAC green book than the m/z that is often used for labeling mass spectra. Sir Joseph John Thomson Sir Joseph John Thomson (18 December 1856 – 30 August 1940), often known as J. J. Thomson, was an English physicist, the discoverer of the electron. ... For usage in mass spectrometry see mass spectrum. ... The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ... International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide. ... Title: Quantities, Units and Symbols in Physical Chemistry Content: the IUPAC green book establishes standards for nomenclature in chemistry. ... It has been suggested that this article or section be merged into Mass_spectrometry. ... The Mass spectrum of any substance is the distribution of matter according to atomic and molecular masses that can be found when a sample of the substance is tested. ...

Today, the thomson is used by some authors of scientific papers, as can be seen in the following examples:

• ASMS
• m/z (Th)
• m/z (Th)
• m/z (Th)
• m/z (Th)
• Mass Spectrometry, Principles and Applications, E. De Hoffmann, J. Charette, V. Stroobant, ISBN0-471-96696-7

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.