A combined linear ion trap time-of-flight system with improved performanceand MSn capabilities

A detailed description of a linear ion trap time-of-flight (TOF) mass spect rometer system, capable of sequential mass spectrometry (MS'), is given. Ma ny improvements have been incorporated since the initial description of thi s system (Rapid Commun. Mass Spectrom. 1998; 12:1463-1474). The pressure in the trap has been lowered from 7.0 to 1.8 mTorr, resulting in an increase in the mass resolution of ion excitation from 75 to 240. Use of the system for MS3 is demonstrated. Dipole excitation of the n = I harmonic, instead o f the n = 0 fundamental frequency of ion motion, is shown to have a higher frequency resolution, f/Deltaf, but lower mass resolution, m/Deltam. Both e xperiments and modeling demonstrate that at the lower pressure there is les s collisional cooling of ions in the axial and radial directions of the tra p. The efficiency of trapping is shown to be nearly 100% for periods up to 5 s. The demonstrated mass range for mass analysis has been extended to gre ater than m/z 16 250. To avoid the formation of adduct ions when trapping p rotein ions for extended times requires ultra-high vacuum cleanliness condi tions, even though the trap operates in the mTorr-pressure range. Upgrading the TOF to a reflectron with higher quality ion optics results in an incre ase in the mass resolution of the TOF mass spectrometer to about 5000 at m/ z 750. Copyright (C) 2001 John Wiley & Sons, Ltd.