Monoisotopic mass determination of macromolecules via mass spectrometry

A method for determining the monoisotopic mass MMono of a macromolecule having a mass of at least 105 Da from a mass Mmono spectrometry spectrum of said macromolecule, the spectrum comprising a set or plurality of isotopic peaks representing an isotope distribution of said macromolecule, comprising the steps of:

• (a) deriving the most abundant mass MMostAb from the set or plurality of isotopic peaks;
• and
• (b) determining the monoisotopic mass MMono from the most abundant mass MMostAb, using the following model
• MMono=α+βMMostAb+ε;
• wherein α+ε is an intersect and β is a scalar slope obtainable by fitting the slope of the plot of the monoisotopic mass in function of the most abundant mass for a plurality of macromolecules from a macromolecule database;
• and ε is a scalar residue of the form ε=εint+εfrac, εint being an integer selected from the group consisting of −2, −1, 0, 1, and 2, and εfrac being a sawtooth function of MMostAb, wherein εfrac=ε−round(ε), with round(ε) being the round function of ε.