SWIFT cyclotron resonance

Fig. 3.12. Series of electrospray ionization Fourier-transform ion cyclotron resonance mass spectra obtained in a two-dimensional mass spectrometry experiment. Proceeding from top to bottom (a) full mass spectrum of a fulvic acid mixture (b) stored waveform inverse Fourier transform (SWIFT) waveform ejection from the ion cyclotron resonance cell of ions of all but a narrow m/z range (c) the resulting isolated parent ion mass spectrum and (d) the product ion mass spectra produced by collision-induced dissociation. Reprinted from Fievre etal. (1997) with permission from the American Chemical Society.

Guan, S. Marshall, A.G. Stored waveform inverse Fourier transform (SWIFT) ion excitation in trapped-ion mass spectrometry theory and applications. Int. J. Mass Spectrom. Ion Processes 1996, 157/158, 5—37 Marshall, A.G. Wang, T-C.L. Ricca, T.L. Tailored excitation for Fourier transform ion cyclotron resonance mass spectrometry. / Am. Chem. Soc. 1985,107, 7893-7897. 

Several methods for constructing a notch waveform have been proposed [34-36]. Marshall developed originally the SWIFT technique [34] for Fourier transform ion cyclotron resonance, FT-ICR, spectrometry. However, because the trajectories of trapped ions in each of an ICR cell and a quadrupole ion trap are characterized by secular frequencies of ion motion, the SWIFT technique can be applied also to the quadrupole ion trap. The SWIFT technique is able to generate a near perfect notch... 

FTICR-MS instruments operate on the principle of ion cyclotron resonance. As ions have resonant frequencies, these frequencies can be used to isolate the ions prior to further fragmentation or manipulation. For example, a resonant frequency pulse on the excite plates (E+/— in Figure 2.8b) will eject the ions at, or near, that frequency. Furthermore, frequency sweeps - carefully defined to not excite the ion of interest - can be used to eject unwanted ions. However, the most elegant method for ion isolation is that of Stored Waveform Inverse Fourier Transform (SWIFT) [86] in which an ion-exdtation pattern of interest is chosen, inverse Fourier-transformed, and the resulting time domain signal stored in memory. This stored signal is then clocked-out, amplified, and sent to the excite plates when needed. The typical isolation waveform in SWIFT uses a simple excitation box with a notch at the frequencies of the ion of interest, a few kHz. 

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