Stored waveform inverse Fourier transform resonance

MS/MS. The capability of trapping ions for long periods of time is one of the most interesting features of FTMS, and it is this capability that has made FTMS (and its precursor, ion cyclotron resonance) the method of choice for ion-molecule reaction studies. It is this capability that has also lead to the development of MS/MS techniques for FTMS [11]. FTMS has demonstrated capabilities for high resolution daughter ion detection [42-44], and consecutive MS/MS reactions [45], that have shown it to be an intriguing alternative to the use of the instruments with multiple analysis stages. Initial concerns about limited resolution for parent ion selection have been allayed by the development of a stored waveform, inverse Fourier transform method of excitation by Marshall and coworkers [9,10] which allows the operator to tailor the excitation waveform to the desired experiment. 

T.-C. L. Wang, T. L. Ricca, and A. G. Marshall, "Extension of Dynamic Range in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry via Stored Waveform Inverse Fourier Transform Excitation," Anal. Chem., IS, 2935-2938. 

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.

Fig. 3.21. (a) Spectrum of a stored waveform inverse Fourier-transform (SWIFT) isolated ion at nominal mass 453 m/z. This molecule is present in dissolved organic matter at the Experimental Nutrient Removal wetland outflow, (b) Spectrum of this ion and resulting products after fragmentation by sustained off-resonance irradiation collision-induced dissociation. Formulae in parentheses represent compositions of lost fragments. From these fragments, unambiguous determination of the elemental composition of the precursor ion at 453 m/z is possible. 

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. 

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. 

Secondary electron multipHer Sustained off-resonance irradiation-CAD Stored waveform inverse Fourier transform Time-to-digital converter... 

Stored waveform inverse Fourier transformation, technique to create excitation waveforms for ions in FT-ICR mass spectrometer or Paul ion traps. An excitation waveform in the time-domain is generated by taking the inverse Fourier transform of an appropriate frequency domain programmed excitation spectrum, in which the resonance frequencies of ions to be excited are included. This procedure may be used for selection of precursor ions in MS/MS experiments. 

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