BROAD-BAND QUADRUPOLAR AXIALIZATION OF LARGE MULTIPLY-CHARGED IONS TOENHANCE MEASUREMENT AND MINIMIZE CONFORMATIONAL RESTRICTIONS

For high-resolution Fourier transform mass spectrometry of electrospra yed proteins, the signal-to-noise ratio of measuring nozzle-skimmer fr agment ions can be improved substantially by their broadband quadrupol ar axialization (QA), even without increasing their concentration in t he ion cyclotron resonance cell. Axialization of the product ions make s possible larger, more concentric ion orbits for measurements. QA all owed the identification of new sequence-indicative product ions from a 29 kDa protein. However, QA of large molecular ions gives little incr ease in signal, consistent with original trapping near the cell axis. By recentering of ions undergoing ion-molecule reactions, these can be carried out at much higher kinetic energy and pressures; for cytochro me c this increases the achievable H-D exchange by 40%, corresponding to exchange at all the active sites of its completely denatured confor mer.