2007 年 55 巻 1 号 p. 51-62
Mass spectrometers separate ions according to each mass/charge value, which is not a dimensionless quantity. However, the m/z value indicated in the abscissa of mass spectra is defined as a dimensionless quantity and not a numerical value the same as the mass/charge value in kilograms/coulombs (kg/C). The numerical value of m/z converted from the mass/charge value depends on the unified atomic mass unit, u (or dalton, Da) and the physical constant “elementary charge,” e that is also the atomic unit of charge. This conversion confuses many mass spectrometrists with regard to the abscissa labeling of mass spectra. To avoid this confusion, a new unit, “thomson” (unit symbol, Th), was proposed, and defined as 1 Th=1 u/atomic charge=1 Da/atomic charge. However, this unit is not yet well known and has been deprecated.