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 allow for studies of ion-ion reactions in the dilute gas-phase is presented. This system utilizes a dual-source design with electrospray ionization for the injection of multiply charged cations and an atmospheric sampling glow discharge interface (ASGDI) for the production of singly char ed anions. The ASGDI source is mounted 90 degrees to the electrospray 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 important instrument capabilities discussed include high mass/high resolution analysis, an ion gate circuit with a variable bipolar output, and use of a TTL pulse for controlling the second (glow-discharge) ion source. Experimental design considerations and representative data from the reactions of multiply charged cations with singly char ed anions including electron transfer (porphyrin systems), proton transfer (peptides and proteins), and adduct formation (anion attachment to various compound classes) are also presented. These data illustrate phenomenologically the reaction types that can be investigated using this Paul-trap-based system. (C) 1997 Elsevier Science B.V.