A novel quadrupole mass spectrometer operating with no dc voltage component on the rods

Abstract

A novel quadrupole mass spectrometer has been developed which has certain clearly defined advantages over the standard instrument. The novelty lies in a re-designed collector assembly which allows special filtering at the exit from the quadrupole lens. This lens operates with an a.c. voltage applied to the pairs of rods, the d.c. component always being zero. The new instrument has the important advantage of a mass discrimination which is not critically dependent upon any operating parameter. This can be significant particularly when operating over a wide mass range. It has been verified for example that, certainly up to 300 a.m.u., discrimination will not change even with a significant change in operating parameters and instrument contamination. With every individual instrument in this series of tests the performance was always better in the new as against the conventional operation. That is, if the d.c. level in the conventional mode was adjusted so that both modes gave the same sensitivity, resolution in the new mode was always significantly better.