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| Mass is a property of physical objects that reveals itself in two ways:
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| # as a resistance to change of velocity (inertia)
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| # as a force when exposed to a gravitational field
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| The symbol for the physical quantity mass is ''m''.
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| The SI unit for mass is '''kg'''. In mass spectrometry it is more common to use the [[Atomic Mass Unit|unified atomic mass unit]] '''u''', which is better called [[Dalton]] '''Da'''.
| | == Related Links == |
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| : ''m'' = n '''Da'''
| | [[Accurate Mass]] |
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| | [[Average Mass]] |
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| In spite of their name, [[Mass Spectrometer | mass spectrometers]] do not measure the mass of ions, but the [[Mass/charge Ratio| mass/charge]] ([[M/Q|m/q]]) of ions.
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| The mass of a particle (atom or molecule) is determined by the following components:
| | [[Exact Mass]] |
| # number of [[Wikipedia:nucleon|nucleons]] (protons and neutrons)
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| # number of electrons
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| # mass defect ([[Wikipedia:binding energy|binding energy]] of nucleons)
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| Because (1) protons and neutrons have simillar masses, and (2) the nucleons dominate the total mass, the total mass of particles is dominated by the number of nucleons. This has the effect that all particle masses are close integer numbers when measured in Dalton. Therefore another quantity has been useful in mass spectrometry, the quantity ''[[nominal mass]]''.
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| However, the term nominal mass is somewhat confusing since it is not clear if it just means a rounded mass or if it means the number of nucleons in a molecule.
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| : [[nucleon number]] ''N'' = n := number of nucleons in molecule
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| : [[Nominal Mass]] ''M'' = n '''Da''' := round(m)
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| : [[base mass]] := mass of the isotope's [[Base Peak|base peak]] = mass of the most abundant isotope
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| : [[Average Mass]] := average mass of isotopes weighted with their natural abundance
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| : [[Accurate Mass]] := same as ''mass'', is sometimes used to differenciate from ''nominal mass''
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| : [[Mass number]] := discontinued, same as ''nucleon number''
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| | [[Monoisotopic Mass]] |
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| | [[Nominal Mass]] |
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