Enhancement of ion transmission at low collision energies via modifications to the interface region of a spectrometer

The transmission efficiency of precursor and product ions decreases significantly at lower collision energies in a four-sector tandem mass spectrometer. In an effort to improve the overall ion transmission in this energy regime three modifications were made in the interface region between the two stages of mass analysis. An einzel lens was inserted prior to the deceleration lens of the collision cell block to reduce the precursor ion beam diameter. The collision cel1 block was reduced in thickness while maintaining the collision path length, thus increasing the number of ions which entered and exited the gas chamber, while removing any stray electrical fields. Finally, a second active focusing element was incorporated after the collision cell block to enhance the collection efficiency of the product ions. A tandem mass spectrum of angiotensin I obtained with this interface, at a collision cell block potential of 9200 volts, exhibited classical high energy collision-induced dissociation (CID) fragmentation patterns, a precursor ion transmission of 92% and an overall CID efficiency of approximately 7.5%. These improvements have resulted in a dramatically higher overall ion transmission at high collision cell potentials as well as sufficient sensitivity in acquiring good quality CID spectra in the lower collision energy regime (i.e., 60 eV). (460-469)