SORI-CID

McDonald, L. A., Barbieri, L. R., Carter, G. T., Krappa, G., Feng, X., Lotvin, J. A., and Siegel, M. M. (2003). FTMS structure elucidation of natural products Application to muraymycin antibiotics using ESI multi-CHEF SORI-CID FTMS(n), the top-down/bottom-up approach, and HPLC ESI capillary-skimmer CID FTMS. Anal. Chem. 75 2730-2739. 

McDonald,L.A. Barbieri, L.R. Carter, G.T. Knippa, G. Feng, X. Lotvin, J.A. Siegel, M.M. FTMS Structure Elucidation of Natural Products Application to Muraymycin Antibiotics Using ESI Multi-CHEF SORI-CID FTMSn, the Top-Down/Bottom-Up Approach, and HPLC ESI Capillary-Skimmer CID FTMS, Anal. Chem. 75(11), 2730-2739 (2003). 

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

SORI-CID is achieved by applying a radio-frequency excitation of a few kHz, above or below the cyclotron frequency (off-resonance) of the selected ion. Thus, the ion packet is accelerated quickly to large and small radii 90° out of phase with the excitation frequency. During this time, neutral target gas molecules are introduced, increasing the pressure in the cell. The ions... 

LeaveU, M.D. Kruppa, G.H. Leary, J.A. Analysis of phosphate position in hexose monosaccharides using ion-molecule reactions and SORI-CID on an FT-ICR mass spectrometer. AwaZ. Chem. 2002, 74, 2608-2611. 

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)... 

SORI-CID, introduced by Gauthier and co-workers [28], is not beset by these problems. As the name suggests, ions are excited slightly off-resonance (500-2000 Hz). Such excitation results in acceleration and deceleration of the ions with a period equal to the difference between the excitation frequency and the ion cyclotron frequency. The periodic decrease in cyclotron radius means that ions are not ejected from the ICR cell. Prior to off-resonance excitation of the precursor ions, inert gas is leaked into the ICR cell. As the ions are excited, collisions with the gas resnlt in conversion of translational energy to internal energy. Again, as a resnlt of the periodic decrease in cyclotron radius, the product ions are formed close to the center of the cell, eliminating resolution issues. It is possible that the product ions have a cyclotron frequency equal to that of the applied excitation waveform. If this were the case, those product ions would be ejected from the ICR cell (resonant ejection). To avoid this occurrence, off-resonance excitation is performed in both directions, for example, 500 Hz. 

A shortcoming of SORI-CID is that gas must be leaked into the ICR cell. However, high resolution FT-ICR measurements require cell low pressure. It is necessary, therefore, to introduce a delay in the experiment following the SORI-CID event. This delay allows the cell pressure to return to normal (ca Ifr Torr). The delay is of the order of tens of seconds, making SORI-CID incompatible with on-line separation techniques. 

In IRMPD [29,30], ions are activated by irradiation with photons in the ICR cell. The photons are provided typically by a 10.6 pm CO2 laser. Precursor ions are heated slowly to their dissociation threshold and, as with SORI-CID, they fragment via the lowest energy pathways. The optimum irradiation time for peptides and proteins is 100-200 ms [29],... 

IRMPD offers a number of advantages over SORI-CID. The principal advantage is that the introduction of gas to the ICR cell is obviated. There is no requirement for a pump-down delay, hence the speed of analysis is greater and the method is compatible with on-line separation techniques [61]. Unlike SORI-CID, blind-spots in the MS/MS spectrum do not occur because there is no resonant excitation of the product ions. All product ions are formed on-axis so there is no loss of resolution and it is possible to undertake further stages of MS/MS. A consequence of the on-axis position is the potential for secondary fragmentation, that is, the product ions can be photon activated also. Fragmentation of product ions can complicate spectral interpretation. 

In BIRD [32], ions are activated by absorption of infrared photons emitted by nearby materials. The vacuum chamber surrounding the ICR cell, when heated normally, emits infrared radiation. This thermal infrared radiation is absorbed by the precursor ions and they are heated close to the temperature of the chamber. As a result, the precursor ions fragment via the lowest energy pathways. Temperatures of up to 500 K are accessible by this method. The rate of dissociation of peptides and proteins at these temperatures is slow and it typically takes 10-1000 s to acquire a BIRD mass spectrum. In addition, long times are needed for the temperature of the ICR cell to equilibrate with that of the vacuum chamber. Unlike SORI-CID, the BIRD technique is neither troubled by the presence of blind-spots in the resulting mass spectra (there is no resonant excitation of product ions), nor are the product ions formed off-axis. 

Methods incorporating FT-ICR MS/MS have been applied also to bottom-up proteomic analyes. Hakansson et al. [66] applied ESI FT-ICR and IRMPD MS/MS to the analysis of glycoproteins isolated from human cerebrospinal fluid. Brock and co-workers [103] combined MALDI FT-ICR with SORI-CID. The throughput of this approach is hampered by the timescales associated with SORI-CID. Laskin and co-workers [104] compared approaches utilizing SORI-CID and SID coupled to ESI. The protein identification scores were comparable for the two techniques. SID has the advantage that no pump-down delay is needed and, therefore, more cycles of MS/ MS can be completed. 

Froesch, M. Bindila, L. Zamfir, A. Peter-Katahnic, J. Siaylation analysis of O-glycosylated siaylated peptides from mine of patients suffering from Schindler s disease by FT-ICR mass spectrometry and SORI-CID. Rapid Commun. Mass Spectrom. 2003,17(24), 2822-2832. 

All the key intermediates were detected by ESI-FTICRMS over time, such as those ions of m/z 707.1,891.2 and 1150.3 (Figure 4.2). After these intermediate ions were further characterized by sustained off-resonance irradiation collision-induced dissociation (SORI-CID), one mechanism was proposed as shown in Scheme 4.3. The mechanism involving the carbopalladation with 2-(2,3-allenyl)malonate yielding the 7t-allyl palladium intermediate (Scheme 4.3) was confirmed. 

Fig. 9.28. Generation of an oscillation of ion kinetic energy as defined by a beat frequency due to off-resonance excitation vertical connections are to locate points of positive and negative interferences, respectively. The larger the amplitude of fi, the more kinetic energy is contained in the circulating ions. One SORI-CID experiment consists of hundreds of beats.

Note CID can rather easily be implemented on FT-ICR instmments because it only demands for a pulse valve and a reservoir. Although the collision gas in SORI-CID can be easily handled, its use is nonetheless in contradiction to the high vacuum requirements of the ICR cell. Thus, alternative ion activation techniques without the use of gas are desirable. 

Mrhalca, R. van der Burgt, Y.E.M. Heck, A.J.R. Heeren, R.M.A. Disulfide Bond Cleavages Observed in SORI-CID of Three Nonapeptides Complexed With Divalent Transition-Metal Cations. J. Mass Spectrom. 2007,42,450-458. 

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