In-series combination of a magnetic-sector mass spectrometer with a time-of-flight quadratic-field ion mirror

A tandem mass spectrometer consisting of a double-focusing magnetic-sector mass analyzer in series with a time-of-flight (TOF) mass analyzer has been designed and constructed. The TOF analyzer was a quadratic-field ion mirror. The method of ionization used was matrix-assisted laser desorption/ionization. Precursor ions were mass selected with the magnetic-sector analyzer, and time focused by ion bunching prior to fragmentation in a collision cell. The fragment ions were mass analyzed with the TOF analyzer, which possessed the property that residence times (i.e., times of flight) in the mirror were independent of ion velocity. The theoretical background to the instrumental design is presented. Experimental results are presented, showing resolutions of 4000 in fragment ion spectra and demonstrating effective high-energy collision-induced decomposition of peptide molecule ions.