Post-source-decay ions

In instrnments withont a reflectron (see Figure 3.7 above), both the precursor and prodnct ions reach the detector at the same time and are not separated. The reflectron, however, is an energy analyser and product ions with different energies, after passage through the reflectron, will have different flight times to the detector and may be separated and their m/z ratios determined. This is known as post-source decay (PSD) [11]. 

Post-source decay The term used to describe the production of product-ion MS-MS spectra in a time-of-flight mass analyser. 

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Note In particular the MALDI-TOF community has coined some sort of an own terminology, e.g., in-source decay (ISD) for all fragmentations occurring within the ion source, post-source decay (PSD) instead of metastable ion dissociation and fragment analysis and structural TOF (FAST) for the specific mode of operation of a ReTOF to detect metastable ions. 

Keki, S., Deak, G., and Zsuga, M., Fragmentation study of rutin, a naturally occurring flavone glycoside cationized with different alkali metal ions, using post-source decay matrix-assisted laser desorption/ionization mass spectrometry, J. Mass Spectrom., 36, 1312, 2001. 

Kaufmann, R., Kirsch, D., and Spengler, B. (1994). Sequencing of peptides in a time-of flight mass spectrometer Evaluation of post source decay following matrix-assisted laser desorption ionization (MALDI). Int. ]. Mass. Spectrom. Ion Processes 131, 355-385. 

Positive Ion Chemical Ionization Photo-Induced Dissociation Post-Source Decay Pyrolysis Mass Spectrometry Quadrupole device used in RF-only mode Quadrupole... 

We have implemented scanning methodologies using MALDI-TOF mass spectrometry to partially purified venom from C. striatus and C. ermineus. We have carried out specific derivatizations in order to deduce composition and sequence information. Together with an intact mass these measurements are used to determine whether an ionized species observed in the MALDI mass spectrum corresponds with the intact protonated molecule of a previously characterized conotoxin. The information obtained from derivatizations is also important when the ionized species does not correspond with the intact mass of peptides of known sequence. In that case, post source decay of the native and derivatized species may help assign the fragment ions. 

Figure 4. Tryptic peptide digest spectrum of spot 6 and post source decay spectrum of a tryptic peptide (T8), MYSPTSILDIR, with mass at m/z 1295.94 from the protein at spot 6. (A) MALDI reflector mass spectrum of tryptic peptide mixture derived from spot 6. (B) Mass spectrometric determination of partial peptide sequence of a tryptic peptide (T8). Y" series ions were observed.

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