US Patent 6849848 Method and apparatus for cooling and focusing ions

Collisional cooling of ions in mass spectrometry has been known for sometime. It is known that collisional cooling can promote focusing of ions along the axis of an ion guide. A similar technique has been used to enhance coupling of a pulsed ion source such as a MALDI source to a Time of Flight instrument. It is now realized that it is desirable to provide, immediately adjacent to a MALDI or other ion source, a low-pressure region to promote ionization conditions most favorable for the particular ion source. Then, with the ions released and free, the ions are subjected to relatively rapid collisional cooling in a high pressure region adjacent to the ionization region. This will dissipate excess of internal energy in the ions, so as to substantially reduce the incidence of metastable fragmentation of the ions. The ions can then be subjected to conventional mass analysis steps.