Library Search Tolerant to Isotopes

A method for acquiring an unknown product ion spectrum and marking isotopic product ion peaks from the unknown product ion spectrum for removal before comparing the unknown product ion spectrum with a library product ion spectrum, comprising:

• ionizing one or more compounds of a sample using an ion source, producing an ion beam of precursor ions;
• receiving the ion beam from the ion source, selecting one or more precursor ions from the ion beam using a precursor ion mass selection window, fragmenting precursor ions within the precursor ion mass selection window, and mass analyzing the resulting product ions using a tandem mass spectrometer, producing an unknown product ion mass spectrum for the precursor ion mass selection window;
• receiving the unknown product ion mass spectrum from the tandem mass spectrometer using a processor;
• retrieving from a memory a library product ion mass spectrum for a known compound using the processor;
• and
• determining, for each peak of the unknown product ion mass spectrum using the processor, if a following peak of the each peak is a non-halogen isotopic peak and,
• if the following peak is a non-halogen isotopic peak, determining if the library product ion mass spectrum includes a peak at the same m/z value of the following peak within a threshold tolerance range and,
• if the library product ion mass spectrum does not include a peak at the same m/z value of the following peak within the threshold tolerance range, removing the following peak from unknown product ion mass spectrum.

A computer program product, comprising a non-transitory and tangible computer-readable storage medium whose contents include a program with instructions being executed on a processor so as to perform a method for acquiring an unknown product ion spectrum and marking isotopic product ion peaks from the unknown product ion spectrum for removal before comparing the unknown product ion spectrum with a library product ion spectrum, the method comprising:

• providing a system, wherein the system comprises one or more distinct software modules, and wherein the distinct software modules comprise a measurement module and an analysis module;
• receiving an unknown product ion mass spectrum from a tandem mass spectrometer using the measurement module, wherein one or more known compounds of a sample are ionized using an ion source, producing an ion beam of precursor ions and wherein the tandem mass spectrometer receives the ion beam from the ion source, selects one or more precursor ions from the ion beam using a precursor ion mass selection window, fragments precursor ions within the precursor ion mass selection window, and mass analyzes the resulting product ions, producing the unknown product ion mass spectrum for the precursor ion mass selection window;
• receiving the unknown product ion mass spectrum from the tandem mass spectrometer using the analysis module;
• retrieving from a memory a library product ion mass spectrum for a known compound using the analysis module;
• and
• determining, for each peak of the unknown product ion mass spectrum using the analysis module, if a following peak of the each peak is a non-halogen isotopic peak and,
• if the following peak is a non-halogen isotopic peak, determining if the library product ion mass spectrum includes a peak at the same m/z value of the following peak within a threshold tolerance range and,
• if the library product ion mass spectrum does not include a peak at the same m/z value of the following peak within the threshold tolerance range, removing the following peak from unknown product ion mass spectrum.