Effect of a pre-filter on the sensitivity of a highresolution quadrupole mass spectrometer

The effect of a pre-filter on the sensitivity of a high-resolution quadrupole mass spectrometer (QMS) has been experimentally studied. The high-resolution QMS uses the condition of a higher stable zone in the Mathieu stability diagram where the higher zone is defined as zone II having a center of a = 2.83 and q = 3.02 in the a-q plane. The pre-filter of a short auxiliary quadrupole was added in front of a main quadrupole and only an r.f. voltage was applied. A helium peak intensity (mass 4 at 50% peak resolution of 40) increased by a factor of two compared with that without the pre-filter, when an r.f. voltage ratio of the pre-filter to the main quadrupole was roughly 0.2. An ion orbit analysis is used to support the experimental result.