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 a nd installed on an external source Fourier transform mass spectrometer with a quadrupole ion guide. This interface is readily interchangeabl e with FAB and MALDI sources, with the main time requirement for chang ing being the pump-down time. A heated capillary, two skimmers and a s et of Einzel lenses are used to deliver ions to the quadrupole ion gui de. 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 neut rals after injection of the ion packet. Kinetic energy distributions o f both small and large biomolecular ions were investigated. For large (10(4)-10(5) Da), highly charged species, the kinetic energy distribut ions were quite favorable to trapping, with sharp peaks at less than 1 0 eV. Thus a 50 ms ion accumulation time is sufficient to obtain spect ra of lysozyme with high S/N ratio. Distributions for smaller ions ten ded to be somewhat wider and peaked at higher energies. The spectra ob tained to date illustrate the ability of the instrument to handle biom olecules ranging from bradykinin to bovine serum albumen.