ION DISSOCIATION REACTIONS INDUCED IN A HIGH-PRESSURE QUADRUPOLE COLLISION CELL

This work concerns a new high-pressure quadrupole collision cell, desi gned for triple-quadrupole mass spectrometers, This new collision cell operates at pressures up to 10 mTorr, an order of magnitude higher th an conventional cells of this type. Previous investigations have conce ntrated upon the significant increases in transmission efficiency and in resolving power for fragment ions which result from the use of this new design, The present work reports an investigation into the nature of the dissociation reactions which can be induced by collisions in t his high-pressure cell, Charge-site-remote fragmentations of a simple precursor ion were chosen as a test case, and were found to be observa ble at laboratory collision energies lower by a factor of 4-5 than tho se found previously to be necessary when using conventional low-pressu re quadrupole collision cells, It was also shown that the charge-site- remote reactions were accompanied by the mixed-site-fragmentation reac tions described by Tuinman and Cook (J. Arm. Soc. Mass Spectrom. Vol. 1, p. 85 (1989)), Ionization of collision gas was observed in the case of xenon, Efforts to observe charge-site-remote fragmentations of pep tide ions were marginally successful. Highly basic peptides, which hav e been problematic for sequencing by low-energy tandem mass spectromet ry, did not yield useful fragment-ion spectra in the new cell, The fra gmentation behaviour of protonated Leu-enkephalin, for which fragmenta tion pathways have been thoroughly studied previously, suggested that the observed spectra reflected integration of the fragmentation kineti cs over a considerably longer time, thus involving many more reaction steps, These combined observations are considered in terms of a qualit ative model based on a rapid decrease of ion kinetic energy during pas sage through the cell, with much longer residence times than for conve ntional quadrupole cells.