MS/MS data processing
A method of identifying precursor ion species from their fragments comprises obtaining mass spectra of a plurality of precursor ion species and their fragments to high mass accuracy. The fragment mass spectrum, obtained from fragmentation of multiple precursor ion species, is then scanned it identify pairs of fragments whose combined mass matches the mass of one of the precursor ion species. Once pairs of fragment ion shave been matched to precursor ions, the composite fragment ion spectrum is broken down into portions, one per fragment pair. Analysis continues until no further pairs are identified. A simplified fragment ion spectrum is then reconstructed for each precursor sample ion by stitching together the broken down sections of the composite fragment spectrum. The resultant reconstructed, simplified fragment spectra are sent to a search engine which returns a score-sorted list of likely candidates for each synthetic fragment ion spectrum.
1. A method of conducting mass spectrometric analysis, comprising steps of:
sequentially isolating ions of a first and a second precursor ion species, the first and second precursor ion species having different mass-to-charge ratios;
combining and storing the isolated ions of the first and second precursor ion species;
fragmenting the combined ions to yield product ions; and
mass analyzing the product ions.
2. The method of claim 1 , wherein the step of sequentially isolating ions of a first and second precursor species is performed by an ion trap.
3. The method of claim 2 , wherein the ions of the first precursor ion species are ejected from the ion trap prior to isolating ions of the second precursor ion species.
4. The method of claim 1 , wherein the step of mass analyzing the ions is performed by an Orbitrap mass analyzer.
5. The method of claim 1 , wherein the step of mass analyzing the ions is performed by a time-of-flight (TOF) mass analyzer.
6. The method of claim 1 , wherein the step of fragmenting the combined ions is performed at a collision cell.
7. The method of claim 1 , wherein the first and second precursor ion species are selected from information contained in a previously acquired precursor mass spectrum.