Monoisotopic Mass?

The current IUPAC-recommended definition of the term "monoisotopic mass" of a chemical species is based on the most abundant isotopes of the constituent elements. It has even been proposed to constrain the definition to be based only on the atomic masses of the most abundant stable isotopes. Such an approach is flawed because in this way several elements and their compounds, in addition to isotopically enriched species, would not merit to be assigned a monoisotopic mass. Furthermore, for large molecules, such as proteins, the monoisotopic mass as currently defined loses its significance. Therefore, we propose to eliminate using the current definition altogether. Instead, the term isotopologue mass should be applied uniformly to every species denoted by a specific chemical formula.