Milli mass unit
Encyclopedia
The milli mass unit or is used as a unit of mass by some scientific authors even though this unit is not defined by the IUPAP red book nor by the IUPAC green book
. It is a short form of the tongue-breaking but formally more correct "milli unified atomic mass unit" (mu) and equivalent to 1/1000 of the unified atomic mass unit (u). A more modern name is the millidalton (mDa)
since the "unified atomic mass unit" is more and more displaced by the unit dalton. (1 Da = 1 u)
Since 1961 the unified atomic mass unit "u" has been defined as 1/12 the mass of 12C. Before that the atomic mass unit "amu" was defined as 1/16 the mass of 16O (physics) and as 1/16 the mass of O (chemistry). Thus the publication date in literature ought to be heeded when reading about the milli mass unit as its name does not reveal whether it refers to the old amu or the newer u.
The mass excess
is usually indicated in mu or mmu.
In mass spectrometry
the mass accuracy of a mass analyzer is often indicated in mu, even though a more correct unit would be mTh since mass spectrometers measure the mass-to-charge ratio
, not the mass. The relative mass accuracy is often indicated in ppm, even though this is no longer supported by the IUPAC green book
which suggests using units like μTh/Th instead of ppm.
IUPAC green book
right|thumb|Front cover of the Green BookQuantities, Units and Symbols in Physical Chemistry Third Edition , also known as the Green Book, published in Aug 2007 by IUPAC is based on the most up to date sources for fundamental constants, data and nomenclature in the field of chemistry and physics...
. It is a short form of the tongue-breaking but formally more correct "milli unified atomic mass unit" (mu) and equivalent to 1/1000 of the unified atomic mass unit (u). A more modern name is the millidalton (mDa)
since the "unified atomic mass unit" is more and more displaced by the unit dalton. (1 Da = 1 u)
Since 1961 the unified atomic mass unit "u" has been defined as 1/12 the mass of 12C. Before that the atomic mass unit "amu" was defined as 1/16 the mass of 16O (physics) and as 1/16 the mass of O (chemistry). Thus the publication date in literature ought to be heeded when reading about the milli mass unit as its name does not reveal whether it refers to the old amu or the newer u.
The mass excess
Mass excess
The mass excess of a nuclide is the difference between its actual mass and its mass number in atomic mass units. It is one of the predominant methods for tabulating nuclear mass. The mass of an atomic nucleus is well approximated by its mass number, which indicates that most of the mass of a...
is usually indicated in mu or mmu.
In mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
the mass accuracy of a mass analyzer is often indicated in mu, even though a more correct unit would be mTh since mass spectrometers measure the mass-to-charge ratio
Mass-to-charge ratio
The mass-to-charge ratio ratio is a physical quantity that is widely used in the electrodynamics of charged particles, e.g. in electron optics and ion optics. It appears in the scientific fields of lithography, electron microscopy, cathode ray tubes, accelerator physics, nuclear physics, Auger...
, not the mass. The relative mass accuracy is often indicated in ppm, even though this is no longer supported by the IUPAC green book
IUPAC green book
right|thumb|Front cover of the Green BookQuantities, Units and Symbols in Physical Chemistry Third Edition , also known as the Green Book, published in Aug 2007 by IUPAC is based on the most up to date sources for fundamental constants, data and nomenclature in the field of chemistry and physics...
which suggests using units like μTh/Th instead of ppm.