AB Sciex QTRAP 4500 LC/MS/MS system System User's Manual
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Operating Instructions — Acquisition Methods4500 Series of Instruments System User Guide56 of 138 RUO-IDV-05-0264-AMS/MS/MS (MS3): In this scan mode, a precursor ion is selected by the Q1 quadrupole andfragmented with collisionally activated dissociation in the Q2 collision cell. The resulting productions are all transmitted to the linear ion trap, where a single product ion is then isolated. Theisolated ion is further fragmented in the linear ion trap, and the resulting product ions arescanned out of the ion trap at one of three scan speeds. As with any in-trap Collision InducedDisassociation (CID) technique, there is a low mass cut-off for the second MS/MS step due to thecondition that the lowest mass fragment and precursor must be simultaneously stable in the trap.For QTRAP® systems, this results in the loss of ions lower than 28 percent of the mass of theprecursor ion during MS3 experiments. This phenomenon is often referred to as the one-thirdcut-off rule.About Spectral Data AcquisitionSpectral data can be acquired in one of three modes, as shown in the following table.ParametersThe working parameters are the set of instrument parameters currently being used.• Source and gas parameters (these parameters can change depending on the ionsource used)• Compound parameters• Resolution parameters• Detector parametersFor more information about instrument parameter values and ranges, refer to Appendix A:Parameters for 4500 Series Instruments.Table 8-1 Spectral Data AcquisitionMode DescriptionProfile The preset value is 0.1 Da. Profile data is the data generated by themass spectrometer and corresponds to the intensity recorded at aseries of evenly spaced discrete mass values. For example, for amass range 100 Da to 200 Da and step size 0.1, the massspectrometer scans 99.95 to 100.05 (records as value 100), 100.05 to101.15 (records as value 101)…199.95 to 200.05 (records as value200).Peak Hopping The preset value is 1.0 Da. Peak Hopping is a mode of operating amass spectrometer in which large steps (approximately 1 Da) aremade. It has the advantage of speed (fewer data steps are made) butwith the loss of peak shape information.Centroid The mass spectrometer scans as in profile mode, but creates acentroid of the data, replacing found peaks with the intensity-weightedcenter of gravity for each peak. Centroid data has the advantage ofsignificantly reducing file size. The disadvantage is that peak shapeinformation is lost, and if data has been collected as a centroid itcannot be altered. We recommend the use of profile mode andcentroiding of the data post-acquisition. |
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