Monoisotopic elements definition

Let us briefly repeat i) the isotopic mass is also the exact mass of an isotope it) the isotopic mass is very close but not equal to the nominal mass of that isotope Hi) accordingly, the calculated exact mass of a molecule or of a mono-isotopic ion equals its monoisotopic mass iv) due to the definition of our mass scale, the isotope represents the only exception from non-integer isotopic mass. As a consequence of these individual non-integer isotopic masses, almost no combination of elements in a molecular or ionic formula has the same calculated exact mass, or simply exact mass as it is often referred to, as any other one [36]. 

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