A dual vacuum chamber Fourier transform mass spectrometer with rapidly interchangeable FAB, MALDI and ESI sources: Electrospray results

A versatile, inexpensive electrospray interface has been constructed and installed on an external source Fourier transform mass spectrometer with a quadrupole ion guide. This interface is readily interchangeable with FAB and MALDI sources, with the main time requirement for changing being the pump-down time. A heated capillary, two skimmers and a set of Einzel lenses are used to deliver ions to the quadrupole ion guide. SIMION (Idaho National Engineering Laboratory, Idaho Falls, Idaho) was used to model ion trajectories and determine optimal dimensions. Five stages of pumping are employed, using mechanical, turbomolecular and cryopumps. A solenoid-driven shutter on the final lens blocks neutrals after injection of the ion packet. Kinetic energy distributions of both small and large biomolecular ions were investigated. For large (10⁴-10⁵ Da), highly charged species, the kinetic energy distributions were quite favorable to trapping, with sharp peaks at less than 10 eV. Thus a 50 ms ion accumulation time is sufficient to obtain spectra of lysozyme with high S/N ratio. Distributions for smaller ions tended to be somewhat wider and peaked at higher energies. The spectra obtained to date illustrate the ability of the instrument to handle biomolecules ranging from bradykinin to bovine serum albumen.