Implementation of Precursor and Neutral Loss Scans on a Miniature Ion Trap Mass Spectrometer and Performance Comparison to a Benchtop Linear Ion Trap

Abstract

Implementation of orthogonal double resonance precursor and neutral loss scans on the Mini 12 miniature rectilinear ion trap mass spectrometer is described, and performance is compared to that of a commercial Thermo linear trap quadropole (LTQ) linear ion trap. The ac frequency scan version of the technique at constant rf voltage is used here because it is operationally much simpler to implement. Remarkably, the Mini 12 shows up to two orders of magnitude higher sensitivity compared to that of the LTQ. Resolution on the LTQ is better than unit at scan speeds of ~ 400 Th/s, whereas peak widths on the Mini 12, on average, range from 0.5 to 2.0 Th full width at half maximum and depend heavily on the precursor ion Mathieu q parameter as well as the pump down time that precedes the mass scan. Both sensitivity and resolution are maximized under higher pressure conditions (short pump down time) on the Mini 12. The effective mass range of the product ion ejection waveform was found to be 5.8 Th on the Mini 12 in the precursor ion scan mode vs. that of 3.9 Th on the LTQ. In the neutral loss scan mode, the product ion selectivity was between 8 and 11 Th on the Mini 12 and between 7 and 8 Th on the LTQ. The effects of nonlinear resonance lines on the Mini 12 were also explored. Graphical Abstract ᅟ.

Two-Dimensional Tandem Mass Spectrometry in a Single Scan on a Linear Quadrupole Ion Trap

“…Figure b shows the experimentally observed relationship between secular frequency and beat frequency using frequency tagging, and converting secular frequency to m / z via Mathieu parameters gives the plot in Figure c. The calibration is shown in blue and the experimentally observed values in red. Lastly, product ions are ejected from the ion trap within hundreds of microseconds of their respective precursor ions being fragmented, and hence, their relationship is preserved in time, just as they were preserved in our implementation of precursor and neutral loss scans. − , …”

“…Lastly, product ions are ejected from the ion trap within hundreds of microseconds of their respective precursor ions being fragmented, and hence, their relationship is preserved in time, just as they were preserved in our implementation of precursor and neutral loss scans. − , …”

“…This work follows our recent experimental demonstration of precursor and neutral loss scans on a single linear ion trap in which orthogonal double resonance was used for mass analysis. − The 2D MS/MS scan similarly utilizes orthogonal double-resonance excitation and can be thought of as conducting every possible precursor ion scan at once (or, correspondingly, every possible neutral loss or product ion scan). The data collection efficiency in 2D MS/MS will be most useful for miniature or portable instruments ,− with low acquisition rates (e.g., DAPI systems). On such instruments data-dependent product ion scans are less favorable than on commercial benchtop systems due to acquisition rate constraints.…”

2D MS/MS Spectra Recorded in the Time Domain Using Repetitive Frequency Sweeps in Linear Quadrupole Ion Traps

“…Additional modifications were made to apply externally controlled low voltage auxiliary waveforms individually to both the x - and y -rod pairs . Nitrogen was used instead of helium as the bath gas in order to improve sensitivity . An uncalibrated ion gauge reading of 1.5 × 10 –5 Torr was used in the experiments.…”

“…28 Nitrogen was used instead of helium as the bath gas in order to improve sensitivity. 29 An uncalibrated ion gauge reading of 1.5 × 10 −5 Torr was used in the experiments.…”