Unified atomic mass unit

Orange Book Entry

This unit (u) is based on the standard that the mass of ¹²C is exactly 12 u. The older symbol, amu, using the standard based on the mass of ¹⁶O is no longer recommended. In biochemistry the term dalton, symbol Da, is sometimes used but is not here recommended.

Gold Book Entry

unified atomic mass unit

Non-SI unit of mass (equal to the atomic mass constant), defined as one twelfth of the mass of a carbon-12 atom in its ground state and used to express masses of atomic particles, u = 1.660 5402(10) x 10^{??????????????????????????27} kg.

IUPAC

Proposed New Entry

Non-SI unit of mass, defined as 1/12 of the mass of the carbon-12 atom in its ground state. The unified atomic mass unit has the symbol u and is not widely used in mass spectrometry, partly because of the clumsy name "unified atomic mass unit" which gets even worse when used with a SI prefix, e.g. "kilo unified atomic mass unit". Therefore it is recomendet to use the supplementary term Dalton. The Dalton is defined as

1 Da = 1 u = 1.660 5402(10) x 10^{??????????????????????????27} kg = 1/12 m(¹²C).

The dalton already is widely used in bio mass spec.

External Links

Wikipedia:Atomic mass