Internal energy deposition in chemical ionization/tandem mass spectrometry.

The efficiency of the collision-induced dissociation (CID) process as a function of the internal energy deposited into the ion during the ionization event was evaluated. (M + H)+ ions of pyrrole, pyrrolidine, pyridine and piperidine (five and six-membered ring heterocyclics) were generated by chemical ionization (CI). The internal energy of the ions was varied by using different reagent gases. Both high-energy (keV) and low-energy (eV) CID were performed on these ions. The experiments showed that the (M + H)+ ions of the five-membered ring compounds, pyrrole and pyrrolidine, have higher fragmentation efficiencies than the six-membered ring compounds, pyridine and piperidine. Fragmentation efficiencies in high-energy CID clearly correlate with the internal energy deposited by the ionization technique. Experiments showed that the low-energy CID process is more sensitive than high-energy CID to changes in internal energy.