PSD = Post source decay

Dissociation of molecules in the "field-free" part. The resulting fragment ions have the same velocity and - in a linear time of flight tube - they would reach the detector at the same time as the precursor ion (parent ion). But the reflectron takes advantage of the fact that the fragments have different energies than their precursor ion. The fragments return their drift already at lower energy levels of the reflectron. The "ion mirror" causes separation of molecules with different energies in one fraction.

Peptide fragmenting happens preferably at the peptide bonds, thus the fragment sizes differ by the sizes of the amino acids. In this way a fragment ion spectrum is achieved, a very efficient way to get information about the primary structure of a peptide.

With the timed ion gate a certain peptide is selected for PSD analysis.

A quadratic field reflectron simplifies the acquisition of PSD spectra and requires only about one tenth of the sample compared to the traditional linear reflectron.

CAF (chemically assisted fragmentation): Tryptic peptides are derivatised by coupling a sulphonyl group to the amino terminus. This increases the fragmentation rate, thus improving the signal to noise ratio. Furthermore, only the positively charged y-ions are reversed by the reflectron, the ions with the intact N-terminus are neutralized by the sulphonyl group, they do not hit the detector. The result is much easier to interpret, because the amino acid sequence can be directly read from the y-ion series.