In-source fragmentation technique for the production of thermalized ions.

Our electrospray ionization-ion funnel-rf hexapole (ESI-IF-6P) source is designed to produce ions for threshold collision-induced dissociation (TCID) studies in a guided ion beam mass spectrometer. This ion source forms an initial distribution of Ca2+(H2O)x ions where x is 6-9. A new in-source fragmentation technique within the hexapole ion guide of the source is described, which is easy to implement and of modest machining and electrical costs, and is able to generate smaller Ca2+(H2O)x complexes, where x = 2-5. Fragmentation is achieved by biasing an assembly of six 0.25 in. long electrodes that are inserted between the hexapole rods. The assembly is positioned in the high-pressure region of the source such that newly formed Ca2+(H2O)x ions undergo enough collisions to become thermalized, as verified by TCID studies. From the initial distribution of ions, fragmentation proceeds along the lowest energy pathway, which corresponds to sequential water loss for most complexes. However, the Ca2+(H2O) complex cannot be formed using this method because charge separation into CaOH+ and H3O+ becomes the lowest energy pathway from the Ca2+(H2O)2 complex. Therefore, this fragmentation technique can be used to identify the critical size complex for M2+(H2O)x systems, which we define as the complex size (x) at which charge separation becomes a lower energy pathway compared with simple ligand loss.

Ion mobility studies of electronically excited States of atomic transition metal cations: development of an ion mobility source for guided ion beam experiments.

The design of an ion mobility source developed to couple to a guided ion beam tandem mass spectrometer is presented. In these exploratory studies, metal ions are created continuously by electron ionization of the volatile hexacarbonyls of the three group 6 transition metals. These ions are focused into a linear hexapole ion trap, which collects the ions and then creates high intensity pulses of ions, avoiding excessive ion losses resulting from the low duty cycle of pulsed operation. The ion pulses are injected into a six-ring drift cell filled with helium where ions having different electronic configurations can separate because they have different ion mobilities. Such separation is observed for chromium ions and compares favorably with the pioneering work of Kemper and Bowers (J. Phys. Chem.1991, 95, 5134). The results are then extended to Mo(+) and W(+), which also show efficient configuration separation. The source conditions needed for high intensities and good configuration separation are discussed in detail and suggestions for further improvements are also provided.