System and method for grouping precursor and fragment ions using selected ion chromatograms
LC/MS data generated by an LC/MS system is analyzed to determine groupings of ions associated with originating molecules. Ions are grouped initially according to retention time, for example, using retention time or chromatographic peaks in mass chromatograms. After initial groupings are determined based on retention time, ion peak shapes are compared to determine whether ions should be excluded. Ions having peak shapes not matching other ions, or alternatively a reference peak shape, are excluded from the group.
1. A method of LC/MS analysis of a complex sample, comprising:
collecting LC/MS data using multiple alternating cycles of high-energy and low-energy fragmentation within a time scale of a chromatographic peak to obtain spectra from high-energy fragment ions and low-energy precursor ions associated with an originating molecule of the complex sample, wherein each of the ions of the spectra has a chromatographic retention time and a peak profile; and
grouping precursor ions and fragment ions that derive from a common originating molecule in response to a correspondence in the chromatographic retention times and one or more characteristics of the peak profiles of the precursor ions and fragment ions.
2. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a peak shape symmetry.
3. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes an apex retention time.
4. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a peak width.
5. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a lift off time of initial detection.
6. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a touch down time of final detection.
7. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a normalized slope.
8. The method of claim 1 , wherein the one or more characteristics of the peak profiles includes a time of an inflection point relative to a time of a peak apex denoting a maximum response.
9. The method of claim 1 , wherein a TOF (time-of-flight)-based instrument is used in analyzing the complex sample to obtain the LC/MS data.
10. The method of claim 1 , wherein said grouping forms a group of ions and excludes from the group any ion having a peak profile that is not similar to peak profiles of other ions in the group.
11. The method of claim 1 , wherein said grouping forms a group of ions and includes ions in the group having a common chromatographic retention time and similar peak profiles.
12. The method of claim 11 , wherein said grouping excludes from the group another ion having a retention time that is the common chromatographic retention time and a peak profile that is not similar to peak profiles of other ions in the group.
13. The method of claim 11 , further comprising:
determining a second group of ions obtained or derived from a database;
comparing the group to the second group; and
determining, on the basis of said comparing, whether the group matches the second group of ions.
14. The method of claim 13 , wherein the second group of ions identifies a molecule and, responsive to determining that the group matches the second group, the method includes identifying the molecule as being included in the complex sample.
15. The method of claim 14 , wherein the second group of ions identifies a molecule that is any of a peptide, a metabolite, and a natural product.
16. A method of analyzing a complex sample, comprising:
receiving spectra obtained from analyzing the complex sample, said analyzing including using multiple alternating cycles of high-energy and low-energy fragmentation within a time scale of a chromatographic peak to obtain the spectra from high-energy fragment ions and low-energy precursor ions associated with an originating molecule of the complex sample, wherein each of the ions of the spectra has a chromatographic retention time and a peak shape; and
grouping precursor ions and fragment ions that derive from a common originating molecule in response to a correspondence in the chromatographic retention times and one or more characteristics of the peak shapes of the precursor ions and fragment ions.
17. The method of claim 16 , wherein the one or more characteristics of the peak shapes includes any one or more of peak shape symmetry, an apex retention time, a peak width, a lift off time of initial detection, a touch down time of final detection, a normalized slope, and a time of an inflection point relative to a time of a peak apex denoting a maximum response.
18. The method of claim 16 , wherein a TOF (time-of-flight)-based instrument is used analyzing the complex sample to obtain the spectra.
19. The method of claim 16 , wherein said grouping forms a group of ions and excludes from the group any ion having a peak shape that is not similar to peak shapes of other ions in the group.
20. The method of claim 16 , wherein said grouping forms a group of ions and includes ions in the group having a common chromatographic retention time and similar peak shapes.
21. The method of claim 20 , wherein said grouping excludes from the group another ion having a retention time that is the common chromatographic retention time and a peak shape that is not similar to peak shapes of other ions in the group.
22. A system comprising:
a processor; and
a memory including code stored therein that, when executed by the processor, performs processing that analyzes a complex sample, the processing comprising:
collecting LC/MS data using multiple alternating cycles of high-energy and low-energy fragmentation within a time scale of a chromatographic peak to obtain spectra from high-energy fragment ions and low-energy precursor ions associated with an originating molecule of the complex sample, wherein each of the ions of the spectra has a chromatographic retention time and a peak profile; and
grouping precursor ions and fragment ions that derive from a common originating molecule in response to a correspondence in the chromatographic retention times and one or more characteristics of the peak profiles of the precursor ions and fragment ions.
23. A system comprising:
a processor; and
a memory including code stored therein that, when executed by the processor, performs processing comprising:
receiving spectra obtained from analyzing the complex sample, said analyzing including using multiple alternating cycles of high-energy and low-energy fragmentation within a time scale of a chromatographic peak to obtain the spectra from high-energy fragment ions and low-energy precursor ions associated with an originating molecule of the complex sample, wherein each of the ions of the spectra has a chromatographic retention time and a peak shape; and
grouping precursor ions and fragment ions that derive from a common originating molecule in response to a correspondence in the chromatographic retention times and one or more characteristics of the peak shapes of the precursor ions and fragment ions.