A 4.7 TESLA INTERNAL MALDI-FTICR INSTRUMENT FOR HIGH-MASS STUDIES - PERFORMANCE AND METHODS

A 4.7 Tesla internal source matrix-assisted laser desorption ionizatio n (MALDI) ion cyclotron resonance (FTICR) (MALDI-FTICR) has been const ructed to examine ions in the 1000-10 000 Da mass range. This instrume nt combines several recent innovations for enhancing the trapping and detection of ions of high mass-to-charge. Ions up to m/z 11 000 have b een efficiently trapped and detected with high signal-to-noise (S/N). By using quadrupolar excitation to axialize ions, resolutions of 1.5 m illion for gramicidin S, 65 000 for insulin, and 85 000 for the 146-me r of polyethylene glycol have been obtained. 100% remeasurement effici ency is shown for 200 remeasurement cycles at m/z 2000 at high S/N wit h normal detection energies. By using quadrupolar excitation for ion r emeasurement, effects from detection parameters such as trapping volta ge and r.f. excitation power are examined under conditions that are in dependent of ionization yield. A tuning method is presented that uses the ions produced by one laser shot to systematically optimize signal strength and resolution for FTICR detection.