What is the Difference Between Monoisotopic Mass and Average Mass?
🆚 Go to Comparative Table 🆚The main difference between monoisotopic mass and average mass lies in the way they are calculated and the assumptions they make about the isotopic composition of a compound:
- Monoisotopic Mass: This is the mass of the isotopic peak whose elemental composition comprises the most abundant isotope of the constituent element. It assumes that every element is present in the most abundant isotope. Monoisotopic mass can be calculated using the atomic masses of the isotopes. It is particularly useful for high-resolution mass spectrometry (HRMS), as it allows for the discrimination of monoisotopic masses.
- Average Mass: This is the weighted average of the isotopic masses, weighted by the isotopic abundances. It is calculated considering all the abundant isotopes of a particular chemical element. The average mass can be calculated using the atomic weights of the elements. It is suitable for low-resolution mass spectrometry (unit mass), as it takes into account the average distribution of isotopes in nature.
In summary, monoisotopic mass is calculated considering a single isotope, while average mass is calculated considering all the abundant isotopes of a particular chemical element.
Comparative Table: Monoisotopic Mass vs Average Mass
Monoisotopic mass and average mass are important parameters in mass spectrometry, which deals with the atoms of particular chemical elements. Here is a table comparing the two:
| Parameter | Monoisotopic Mass | Average Mass |
|---|---|---|
| Definition | The mass of a single isotope of an element | The weighted average of the isotopic masses of an element, weighted by their abundances |
| Calculation | Calculated using the atomic masses of the isotopes | Calculated using the atomic weights of the elements |
| Mass Spectrometry | Relevant for small molecules, where the base peak corresponds to the monoisotopic ion ([M+H]+ or [M -H]-) | Relevant for larger molecules, such as peptides, where the monoisotopic mass may not be the base peak |
| Base Peak | Monoisotopic mass is the base peak for most small molecules | Average mass does not appear in the spectrum and is not the base peak for larger molecules |
In summary, monoisotopic mass is calculated considering a single isotope, while average mass is calculated considering all the abundant isotopes of a particular chemical element. Monoisotopic mass is relevant for small molecules, where the base peak corresponds to the monoisotopic ion, while average mass is relevant for larger molecules, such as peptides, where the monoisotopic mass may not be the base peak.
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