Isotope Pattern
The distribution of molecular masses that the natural isotopic composition of the elements produces — the M, M+1, M+2 series a mass spectrum shows — together with the monoisotopic and average mass.
- You supply
- A chemical formula, in the same grammar every other page here uses. Whole atoms only: a pattern describes one molecule, so a fractional stoichiometry is refused rather than rounded. Write a charge into the formula (
SO4^2-,Na+) and every mass becomes m/z, electron mass included. - Reading it
- Abundances are relative to the tallest peak, which is not always the monoisotopic one — for tin or a polybrominated compound it is not. This is an exact combinatorial result, not a simulated spectrum: no resolution, no peak shape, no adducts and no fragmentation.
Worked examples: a nickel complex · dibromomethane · tin tetrachloride · a sulfate anion
Input
Results
| formula: | CH2Br2 |
|---|---|
| monoisotopic mass: | 171.85233 |
| average mass: | 173.8337 |
| base peak: | 173.8503 |
Pattern
| mass | nucleons | relative / % | abundance |
|---|---|---|---|
| 171.8523 | 172 | 51.40 | 25.414 % |
| 173.8503 | 174 | 100.00 | 49.444 % |
| 174.8537 | 175 | 1.10 | 0.546 % |
| 175.8482 | 176 | 48.64 | 24.049 % |
These are the relative abundances that follow from the natural isotopic composition of the elements — an exact combinatorial result, not a simulated spectrum. There is no instrument here: no resolution, no peak shape, no adducts and no fragmentation. Combinations with the same number of nucleons are shown as one peak at their abundance-weighted mass, which is what an instrument of ordinary resolving power sees; at high resolution several of these would split. Abundances are relative to the tallest peak, which is not always the monoisotopic one.