ADAPTATION OF THE PAUL-TRAP FOR STUDY OF THE REACTION OF MULTIPLY-CHARGED CATIONS WITH SINGLY CHARGED ANIONS

The adaptation of a quadrupole ion trap mass spectrometer (QITMS) to a llow for studies of ion-ion reactions in the dilute gas-phase is prese nted. This system utilizes a dual-source design with electrospray ioni zation for the injection of multiply charged cations and an atmospheri c sampling glow discharge interface (ASGDI) for the production of sing ly char ed anions. The ASGDI source is mounted 90 degrees to the elect rospray interface to facilitate anion injection through a 3 mm hole in the ring electrode. Independent control of the two ion sources allows for selection of the oppositely charged reacting species. Other impor tant instrument capabilities discussed include high mass/high resoluti on analysis, an ion gate circuit with a variable bipolar output, and u se of a TTL pulse for controlling the second (glow-discharge) ion sour ce. Experimental design considerations and representative data from th e reactions of multiply charged cations with singly char ed anions inc luding electron transfer (porphyrin systems), proton transfer (peptide s and proteins), and adduct formation (anion attachment to various com pound classes) are also presented. These data illustrate phenomenologi cally the reaction types that can be investigated using this Paul-trap -based system. (C) 1997 Elsevier Science B.V.