Low-collision energy

For a slow ion of 1 eV kinetic energy (E, b =1) and mass iDj = 100 colliding with a helium atom (m = 4), the collisional energy E m = 0.04 eV. Only small changes in rotational energy can be expected from such low energy collisions. 

The hybrid has other advantages of sensitivity, low signal-to-noise ratio, fast switching between MS and MS/MS modes, use with continuous or pulsed ion sources, and use with high- or low-energy collision-induced ion decomposition. 

Figure 12.4 MALDI analysis of peptides prepared in situ from a 10 1 mixture of Bacillus cereus and Bacillus anthracis sp. Sterne.82 (a) Survey spectrum of peptide products. Species assignments are indicated on the figure. (b) Spectrum of fragment ions produced by low-energy collisions of the Bacillus cereus-specific peptide of mass 1529. (c) Spectrum of fragment ions produced by low-energy collisions of ions of the Bacillus anthracis peptide of mass 1528.

Tabb, D. L. Huang, Y. Wysocki, V. H. Yates, J. R. Influence of basic residue content on fragment ion peak intensities in low-energy collision-induced dissociation spectra of peptides. Anal. Chem. 2004, 76,1243-1248. 

Gilardini, A. (1972), Low Energy Collisions in Gases, ch. 1, Wiley, New York. 

The main principles of de novo sequencing will be discussed here using a few d spectra that were acquired using an ion trap mass spectrometer equipped with an electrospray ion source, under low energy collision induced dissociation (CID). 

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. 

Huang and Freiser (132, 133) were able to prepare exohedral metal C60 ions [MC60]+ by direct reaction of the bare metal ions Fe+, Ni+, Co+, Cu+, Rh+, and La+ with Cgo vapor produced from a heated probe. The [MC60]+ ions when subjected to low-energy collision-induced dissociation with argon all produced the Cg0 ion. These results show that the metal ions attach to the outer surface of C60. The exohedral metallofullerene ions differ from the endohedral metallofullerenes produced by laser ablation of metal oxide-graphite mixtures and support the observations of Smalley and co-workers (148) who found that endohedral metallofullerene ions dissociate by loss of C2 units. 

Negative atmospheric pressure chemical ionization (APC) low-energy collision activation mss spectrometry has also been employed for the characterization of flavonoids in extracts of fresh herbs. Besides the separation, quantitative determination and identification of flavonoids, the objective of the study was the comparison of the efficacy of the various detection systems in the analysis of flavonoids in herb extracts. Freeze-dried herbs (0.5g of chives, cress, dill, lovage, mint, oregano, parsley, rosemary, tarragon and thyme) were ground and extracted with 20 ml of 62.5 per cent aqueous methanol. After sedimentation the suspension was filtered and used for HPLC analyses. Separations were carried out in an... 

U. Justesen, Negative atmospheric pressure chemical ionisation low-energy collision activation mass spectrometry for the characterisation of flavonoids in extracts of fresh herbs. J. Chromatogr. A 902 (2000) 369-379. 

Scans based on resonant ejection may either be carried out in a forward, i.e., from low to high mass, or a reverse manner. This allows for the selective storage of ions of a certain m/z value by elimination of ions below and above that m/z value from the trap. Thus, it can serve for precursor ion selection in tandem MS experminents. [156,158] Axial excitation can also be used to cause collision-induced dissociation (CID) of the ions as a result of numerous low-energy collisions with the helium buffer gas that is present in the trap in order to dampen the ion motion. [150,156] A substantial increase of the mass range is realized by reduction of both the RF frequency of the modulation voltage and the physical size of theQIT. [154,159,160]... 

Figure 4.3 Representative Cl mass Figure 4.4 Low-energy collision-spectra of quadricyclane showing changes indnced dissociation patterns for CyHs with flow tube temperature (a) 973 K isomers, showing clear differences (6) 573 K and (c) 298 K (a) quadricyclane (6) norbornadiene and...

Ma, Y.L. et al.. Internal glucose residue loss in protonated 0-diglycosyl flavonoids upon low-energy collision-induced dissociation, J. Am. Soc. Mass Spectrom., 11, 136, 2000. 

Distonic ions reacting primarily at the radical center provide the opportunity to study free radical reactions in the gas phase by MS. For example, 4-dehydroanilin-ium ions (37 +, m/z = 93) were generated by multiple low-energy collisions of chloro-, bromo-, or iodoanilinium ions (36+, m/z = 220) with argon. This distonic species reacted with dimethyl sulfide by abstraction of thiomethyl (MeS ), that is, as a reactive radical with an inert charge site. However, 37 + can be deprotonated by pyridine. 2° ... 

In Sections II-IV it is demonstrated that rotationally state-selected ions can be produced in sufficient quantities to study reactions. Product ions for low-energy collisions ( Coii values of 0.04-0.24 eV) have only been detected to date in the reaction of H + H2, but it is likely that this method should be reasonably general. 

S. B. Levery, M. S. Toledo, R. L. Doong, A. H. Straus, and H. K. Takahashi, Comparative analysis of ceramide structural modification found in fungal cerebrosides by electrospray tandem mass spectrometry with low energy collision-induced dissociation of Li + adduct ions, Rapid Commun. Mass Spectrom., 14 (2000) 551-563. 

---