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Nominal mass is a term used in high level mass spectrometric discussions, it can be calculated using the mass number of the most abundant isotope of each atom, without regard for the mass defect. For example, when calculating the nominal mass of a molecule of nitrogen (N 2) and ethylene (C 2 H 4) it comes out as. N 2 (2*14)= 28 Da C 2 H 4
The exact mass of an isotopic species (more appropriately, the calculated exact mass [9]) is obtained by summing the masses of the individual isotopes of the molecule. For example, the exact mass of water containing two hydrogen-1 (1 H) and one oxygen-16 (16 O) is 1.0078 + 1.0078 + 15.9949 = 18.0105 Da.
Archaeological materials, such as bone, organic residues, hair, or sea shells, can serve as substrates for isotopic analysis. Carbon, nitrogen and zinc isotope ratios are used to investigate the diets of past people; these isotopic systems can be used with others, such as strontium or oxygen, to answer questions about population movements and cultural interactions, such as trade.
The term isotopes (originally also isotopic elements, [4] now sometimes isotopic nuclides [5]) is intended to imply comparison (like synonyms or isomers). For example, the nuclides 12 6 C, 13 6 C, 14 6 C are isotopes (nuclides with the same atomic number but different mass numbers [6]), but 40 18 Ar, 40 19 K, 40 20 Ca are isobars (nuclides with ...
Samples must be introduced to the mass spectrometer as pure gases, achieved through combustion, gas chromatographic feeds, [6] or chemical trapping. By comparing the detected isotopic ratios to a measured standard, an accurate determination of the isotopic make up of the sample is obtained. For example, carbon isotope ratios are measured ...
The relative isotopic mass (see section below) can be obtained by dividing the atomic mass m a of an isotope by the atomic mass constant m u yielding a dimensionless value. Thus, the atomic mass of a carbon-12 atom is 12 Da by definition, but the relative isotopic mass of a carbon-12 atom is simply 12.
The δ values and absolute isotope ratios of common reference materials are summarized in Table 1 and described in more detail below. Alternative values for the absolute isotopic ratios of reference materials, differing only modestly from those in Table 1, are presented in Table 2.5 of Sharp (2007) [1] (a text freely available online), as well as Table 1 of the 1993 IAEA report on isotopic ...
In a typical gas chromatography analysis, isotopic dilution can decrease the uncertainty of the measurement results from 5% to 1%. It can also be used in mass spectrometry (commonly referred to as isotopic dilution mass spectrometry or IDMS), in which the isotopic ratio can be determined with precision typically better than 0.25%. [5]