Sustained off resonance

The energy imparted to the ions depends on the energy of the rf pulse and the duration of the pulse. The energy does not have to be raised in one event but may be absorbed by the ion in small portions. A technique called sustained off-resonance excitation (SORT) (82) uses a low-amplitude rf pulse that is off-resonance to the ion cyclotron frequency. The difference of the cyclotron frequency and the excitation frequency (-500 Hz) causes the ion to experience in- and out-of-phase excitation that has the effect of a repeated expansion and shrinkage of the cyclotron orbit. In this process, the ion undergoes a large number of low-energy collisions and the Ecom slowly increases until the ion dissociates. 

Gauthier, J.W. Trautman, T.R. Jacobson, D.B. Sustained Off-Resonance Irradiation for Collision-Activated Dissociation Involving FT-ICR-MS. CID Technique That Emulates Infrared Multiphoton Dissociation. Anal. Chim. Acta 1991,246,211-225. 

Hofstadler, S. A., Wahl, J. H., Bakhtiar, R., Anderson, G. A., Bruce, J. E., and Smith, R. D. (1994). Capillary electrophoresis/Eourier-transform ion-cyclotron-resonance mass spectrometry with sustained off-resonance irradiation for the characterization of protein and peptide mixtures. ]. Am. Soc. Mass Spectrom. 5, 894 —899. 

FT-ICR instruments are also capable of performing MS" experiments. The most popular method of ion activation is sustained off-resonance irradiation (SORI), where ions are excited to a larger cyclotron radius using rf energy, undergo collisions with a neutral gas pulsed into the cell and dissociate. Other methods are available, including infrared multiphoton dissociation (IRMPD)65 and electron capture dissociation (ECD)66 which is of particular value in glyco-peptide analysis (Section VIA). 

Gauthier, J.W., Trautman, T.R. and Jacobson, D.B. (1991) Sustained off-resonance irradiation for collision-activated dissociation involving Fourier transform mass spectrometry. Collision-activated dissociation technique that emulates infrared multiphoton dissociation. 

Hettich, R.L. and Stemmier, E.A. (1996) Investigation of oligonucleotide fragmentation with matrix-assisted laser desorption ionization Fourier-transform mass spectrometry and sustained off-resonance irradiation. Rapid Commun. Mass Spectrom., 10 (3), 321-7. 

Other fragmentation techniques have been introduced [108]. Some of these, e.g., sustained off-resonance irradiation (SORl) and infrared multiphoton dissociation (IRMPD), provide similar fragmentation as in CID, i.e., preferential backbone cleavages at the peptide amide bond (b- and y-ions). Others like electron-capture dissociation (ECD) [109-110] induce different fragmentation reactions, i.e., the formation of c- and z -ions due to cleavage of N-C bonds. 

Initial results with the fragmentation of multiple-eharge protein ions in FT-ICR-MS were achieved, either by in-source CID [159], sustained off-resonance irradiation (SORI) [160], or infrared multiphoton dissoeiation (IRMPD) [161], and later on with electron-capture dissociation [109-110]. 

Dissociation by collisions with a neutral target, or sustained off-resonance irradiation collision-induced dissociation (SORI-CID) (Amster, 1996). 

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. 

Pastor, S. J. and Wilkins, C. L., Sustained off-resonance irradiation and collision-induced dissociation for structural analysis of polymers by MALDI-FTMS, Int J. Mass Spectrom. Ion Processes, 175, 81, 1998. 

Fragmentation of peptide and protein ions in FT-ICR mass spectrometry may be induced by sustained off-resonance irradiation collision-induced dissociation (SORI-CID) [28], infrared multiphoton dissociation (IRMPD) [29,30], blackbody infrared radiative dissociation (BIRD) [31,32], surface-induced dissociation (SID) [33,34], and electron capture dissociation (ECD) [35,36]. These techniques are true MS/MS techniques in which the precursor ion is isolated prior to fragmentation. Additional techniques in which ions are not isolated but fragmented before they... 

Sustained Off-Resonance Irradiation CottisioN-iNDUCED Dissociation (SORI-CID)... 

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