Paul traps mass selective instability scan

Louris, J.N. Schwartz, J.C. Stafford, G.C. Jr. Syka, J.E.P. Taylor, D.M. The Paul ion trap mass selective instability scan trap geometry and resolution. Proc. 40th ASMS Conference on Mass Spectrometry and Allied Topics, Washington DC, 1992, 1003-1004. 

Like most successful clever ideas, the mass selective instability scan mode seems rather simple once someone had conceived it. However, it turned out (Stafford 1984) that full experimental reahzation of the potential of the method required another innovation, the exploitation of the collisional coohng/focusing effect of a low pressure of helium, discussed above. It was found (Stafford 1984) that the presence of helimn at a relatively high pressure of approximately 10 torr significantly enhanced the mass resolution, sensitivity and detection limit of a Paul ion trap operated as a mass spectrometer using the mass selective instability scan to obtain the mass spectrum. 

Figure 6.21 Partial spectra illustrating the dramatic effect of use of helium as a damping gas in a Paul trap on its paformance as a mass spectrometer using the mass selective instability scan mode. Peaks on the left are for mtz 69, those on the right for m/z 502. The top spectra were obtained without damping gas, and the bottom spectra by using 10 torr of helium. Reproduced from Stafford, Int. J. Mass Spectrom. Ion Proc. 60, 85 (1984), copyright (1984), with permission from Elsevier.

The mass selective instability scan represented an enormous advance in the exploitation of the Paul trap as a mass spectrometer but was limited with respect to the available 650 (see above) for a trap of reason-... 

Figure 6.22 Scan function used to obtain an El mass spectrum (one microscan) using a Paul trap with mass selective instability scanning with concurrent axial modulation. The scan function shows the ionization period A (this could be replaced by a period of ion injection from an external source), followed immediately by activation of the axial modulation waveform and the analytical ramp of Vg. Note that the pre-scan for the automatic gain control function is not shown. Reproduced from March, J. Mass Spectrom. 32, 351 (1997), with permission of John Wiley Sons, Ltd.

Figure 2.28 Ion trap scan function. The sequence of events used to generate a mass spectrum in a typical Paul trap is shown. This sequence is typically repeated many times with the individual spectra summed or averaged to produce the final spectrum. The generic parts of the scan function shown include (1) ion injection and trapping, (2) ion relaxation/cooling, (3) auxiliary excitation for selective ejection/storage of desired ions and (4) mass-selective instability scan. The timing of the resonant excitation function is also indicated two sine waves shown indicate a first pulse for selective excitation and a second pulse for enhancing the mass selective instability scan...

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