Sustained Off-Resonance Irradiation-CID in ICR Cells

CID still is widely used as an activation technique for tandem MS in FT-ICR in-stmments. The collision gas is admitted into the ICR cell through a pulsed valve. To avoid detrimental effects of the collision gas on the ultra-high vacuum of the ICR cell ( 10 ° mbar) the gas is admitted from a low pressure vessel ( 10 mbar) in short pulses (5-50 ms). This causes the cell pressure to rise to levels ( 10 mbar) that do not compromise the resolving power of FT-ICR in a noteworthy manner. To further reduce the interference with collision gas, a pump delay (1-5 s) can be inserted between CID and tn/z analysis. Generally, a set of such cycles is accumulated to obtain a spectmm. 

For effective dissociation CID requires that the ions collide sufficiently fast with the collision gas. The increase in ion kinetic energy is classically effected by short (0.1-0.5 ms) excitation at the cyclotron frequency of the precursor ion 

Example MALDI-SORI-FT-ICR spectra of the 2-aminobenzamide derivative of an unknown oligosaccharide were used for structure elucidation. First, the [M-i-Na] ion, m/z 1240.5, was selected and fragmented (MS, Fig. 9.29a), then selected fragments thereof were subjected to further dissociation to illustrate the principle, only one of these has been included here (MS, Fig. 9.29b). The frequency for SORI was chosen at 1.5% distant from the respective precursor ion s cyclotron frequency and supplied with an amplitude Esori = 10 V [133]. 

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