On the Time Scale of Internal Energy Relaxation of AP-MALDI and nano-ESI ions in a Quadrupole Ion Trap

摘要

The use of matrix assisted laser desorption ionization (MALDI) and nano-electrospray ionization (nano-ESI) have become essential means for ionizing high molecular weight biomolecules. Recently reported results[1] on the cooling of atmospheric pressure (AP)-MALDI and nano-ESI generated ions in a quadrupole ion trap mass spectrometer (QITMS) are inconsistent with measured collisional cooling rates.[2-4] The reported experiments were therefore repeated using a QITMS with a custom interface amenable to both nano-ESI and AP-MALDI. The relative internal energies of several peptides were probed with energy resolved collision induced dissociation (CID) at various times after ion isolation. It will be shown that the time required for the ions to reach internal energy equilibrium after parent ion isolation is on the order of milliseconds. Furthermore, it will be shown that the high space charge conditions used in the previous work could have complicated their results by shifting the ion secular frequency at different portions of the experiment.