Can monoisotopic mass and average mass be used interchangeably?

No. They are different calculations. Quote the basis the laboratory printed.

Is monoisotopic mass the labeled milligram size?

No. It is a molecular mass, typically in daltons. The shop milligram figure is a catalog fill size.

Glossary · 2026-09-24

Monoisotopic mass, laboratory definition

Monoisotopic mass is calculated from the most abundant isotope of each element in the formula. Average molecular weight uses the weighted natural mix of isotopes. The two numbers are close and easy to swap, which is why a peptide report should say which calculation it compared with the observed ion. If it does not say, do not choose one in the margin.

Salt form and adducts move the target again. Free peptide, acetate, and trifluoroacetate are different formulas. Read molecular weight and the COA guide before you file a match. Research-use only.

Frequently asked questions

Can monoisotopic mass and average mass be used interchangeably?: No. They are different calculations. Quote the basis the laboratory printed.
Is monoisotopic mass the labeled milligram size?: No. It is a molecular mass, typically in daltons. The shop milligram figure is a catalog fill size.

Research-use only. BlueNex Labs does not provide medical or veterinary advice. Confirm your institution’s policies before purchase.