UBC Theses and Dissertations
A new linear ion trap time of flight instrument with tandem mass spectrometry capabilities Campbell, Jennifer Mary
This thesis summarizes the construction and characterization of a novel hybrid mass spectrometer with tandem mass spectrometry capabilities, named the linear ion trap time of flight mass spectrometer. In a "linear ion trap" ions are trapped in a 2-dimensional quadrupolar potential by the application of timed stopping potentials on entrance and exit apertures. The performance characteristics of the linear ion trap as a storage device are initially assessed using a modified triple quadrupole mass spectrometer. On the time scales for tandem mass spectrometry, injection, extraction, and trapping efficiencies are all near 100%. The modified operation of the triple quadrupole mass spectrometer is used to study the kinetics of dissociation of gas phase holomyoglobin in high charge states. The results indicate that the binding of the heme group is relatively unaffected by intramolecular repulsion resultant from excess charge. To construct the linear ion trap time of flight mass spectrometer, a linear ion trap is orthogonally coupled to a linear time of flight mass analyzer. The mass resolutions of the spectrometer could be optimized to attain resolutions near 700. Tandem mass spectrometry in the linear ion trap is enabled by superimposing a dipolar excitation voltage on the quadrupolar field by coupling an auxiliary waveform generator to a pair of the quadrupole rods. This voltage is used to effect precursor isolation via a broadband waveform followed by collision induced dissociation through mass selective resonant excitation. The resulting fragment ions are detected in the time of flight mass spectrometer. With 7 mTorr N 2 as the collision gas, the resolutions of ion isolation and excitation are ~ 40 and 70, respectively. Fragmentation efficiency is near 60 %. When a lower pressure is used, the same resolutions increase to 100 and 250, respectively. It is found that the resolution of resonant excitation is strongly dependent upon amplitude of the applied voltage.
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