Mass spectrometry precursor ion selection
AssigneeShimadzu Research Laboratory (Europe) Ltd.
InventorsMichael May, JingWen Yao
Life of this patent
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Abstract
The present invention is concerned with methods for the selection of precursor ions of a sample polypeptide for fragmentation in mass spectrometry, together with methods for determining at least one putative amino acid sequence for a sample polypeptide, apparatus and computer programs for same.
Claims9
A method for selecting a precursor ion of a soft ionisation mass spectrum of a partially degraded sample polypeptide for fragmentation, said soft ionisation mass spectrum comprising a set of m/z peaks of ion species obtained from said partially degraded sample polypeptide, said method comprising the steps of:
- (i) with at least two candidate m/z peak sets determined from said soft ionisation mass spectrum, each m/z peak in each candidate m/z peak set differing from its at least one neighbour by the mass of an amino acid, and a putative amino acid sequence determined from each candidate m/z peak set, each amino acid sequence being that of the amino acids which correspond to the mass differences between each m/z peak and its at least one neighbour;
- and
- (ii) analysing using fuzzy logic principles said m/z peaks of said at least two candidate m/z peak sets, to select at least one m/z peak for fragmentation.
A method for determining at least one putative amino acid sequence for a partially degraded sample polypeptide said method comprising the steps of:
- (i) obtaining a soft ionisation mass spectrum of said partially degraded sample polypeptide giving a set of m/z peaks of ion species obtained from said partially degraded sample polypeptide;
- (ii) determining at least two candidate m/z peak sets from said soft ionisation mass spectrum, said soft ionisation mass spectrum comprising a set of m/z peaks of ion species obtained from said partially degraded sample polypeptide, each m/z peak in each candidate m/z peak set differing from its at least one neighbour by the mass of an amino acid, and determining a putative amino acid sequence from each candidate m/z peak set, each amino acid sequence being that of the amino acids which correspond to the mass differences between each m/z peak and its at least one neighbour;
- (iii) analysing using fuzzy logic principles said m/z peaks of said at least two candidate m/z peak set, to select at least one m/z peak for fragmentation;
- (iv) obtaining a further soft ionisation mass spectrum of said selected at least one m/z peak, giving a set of m/z peaks of ion species;
- (v) optionally repeating steps (ii)-(iv), using at least two of the previously obtained soft ionisation mass spectra as the said soft ionisation mass spectrum;
- and
- (vi) determining an at least two candidate m/z peak set from said soft ionisation mass spectra, said soft ionisation mass spectra comprising a set of m/z peaks of ion species obtained from said partially degraded sample polypeptide, each m/z peak in each candidate m/z peak set differing from its at least one neighbour by the mass of an amino acid, and determining a putative amino acid sequence from each candidate m/z peak set, each amino acid sequence being that of the amino acids which correspond to the mass differences between each m/z peak and its at least one neighbour.
Dependencies are inferred from the claim text.