MARKET 1 Lecture Notes - Lecture 4: Mass Spectrum, Natural Abundance, Ethane
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Different masses: average atomic mass (standard atomic weight) not used in ms, exact atomic mass (relative atomic mass, nominal atomic mass, accurate mass, monoisotopic mass, mass considering the main isotopes. Examples: carbon, average: 12. 0107, nominal: 12, accurate exact: 12. 000 (12c, chlorine, average: 35. 45, nominal: 35 and 37, accurate exact: 34. 9689 (35cl) and 36. 9659 (37cl) The average mass of a molecule is obtained by summing the average atomic masses of the constituent elements. The monoisotopic mass is the sum of the masses of the atoms in a molecule using the unbound, ground-state, rest mass of the most abundant isotope for each element instead of the isotopic average mass. Monoisotopic mass is typically expressed in unified atomic mass units or daltons (da) The accurate mass (the measured accurate mass) is an experimentally determined mass that allows the elemental composition to be determined. For molecules with mass below 200 u, 5 ppm accuracy is often sufficient to uniquely determine the elemental composition.
