Abstract

A 4.7 Tesla internal source matrix-assisted laser desorption ionization (MALDI) ion cyclotron resonance (FTICR) (MALDI-FTICR) has been constructed to examine ions in the 1000–10000 Da mass range. This instrument 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 been efficiently trapped and detected with high signal-to-noise (S/N). By using quadrupolar excitation to axialize ions, resolutions of 1.5 million for gramicidin S, 65 000 for insulin, and 85 000 for the 146-mer of polyethylene glycol have been obtained. 100% remeasurement efficiency is shown for 200 remeasurement cycles at m/z 2000 at high S/N with normal detection energies. By using quadrupolar excitation for ion remeasurement, effects from detection parameters such as trapping voltage and r.f. excitation power are examined under conditions that are independent 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.

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