A VARIABLE DISPERSION ARRAY DETECTOR FOR A TANDEM MASS-SPECTROMETER

Incorporation of a pair of quadrupole lenses and one octapole lens after the second magnetic field of a JEOL HX110/HX110 tandem mass spectrometer permits varying the dispersion and therefore the mass range that can be focused on a 2 in array detector. This range can be adjusted from a value of 1:1.04 to 1:1.3 for the ratio of low m/z to high m/z falling at the extremes of the detector. The ratio is governed by the d.c. potentials on the lenses which also changes the angle of the resulting focal plane and thus requires that the position of the array detector must be changed accordingly. In the system described, all these variables are under computer control and can be adjusted within 1 s, thus allowing for a change even during the recording of a spectrum if one wishes to minimize the number of segments to be recorded to cover the entire spectrum while still maintaining unit mass resolution. The variable range array detector is useful for the recording of normal mass spectra as well as those generated upon collision induced decomposition (CID) of precursor ions. In the latter case, the refocusing of the ion beams through the quadrupole lens system is more complex but the software controls the lens potentials accordingly. The system has been used to record the normal or CID spectra of peptides, either from a static sample or eluting from a high performance liquid chromatograph.