Adjusting the Resolving Power of a Sector Instrument

Example The influence of relative slit width on peak shape and resolution is demonstrated on the second isotopic peak of toluene molecular ion, m/z 94 (Fig. 4.21). With the entrance sht at 50 pm and the exit sht at 500 pm the peak is flat-topped leji), because a narrow beam from the entrance sweeps over the wide open detector slit keeping the intensity constant as the scan proceeds until the beam passes over the other edge of the sht. Closing the exit slit to 100 pm 

Note The ultimate resolution of a magnetic sector mass spectrometer is reached when the slits are closed to a width of a few micrometers. Often, the slit height is also reduced, e.g., from 5 to 1 mm In daily work, the resolution will be set to fit the actual task, e.g., R = 1000-2000 for low-resolution work, R = 3000-5000 if accurate mass determination at high scan rates is needed (GC-MS, Chap. 14) or isotopic patterns of high mass analytes have to be resolved, orR = 7000-15,000 in slow-scanning accurate mass measurements. 

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