Numerical investigation of the effect of electrode size on the behaviour of quadrupole mass filters

The behaviour of a quadrupole mass spectrometer (QMS) for variation in rod size has been investigated using a numerical approach reported previously. Behaviour is found to vary significantly with the change in rod size and the optimum rod size suggested is closer to that used in some commercial QMS instruments than to the value from analytical approaches. The results allow an upper limit to manufacturing tolerances to be inferred. The present work also confirms that the size of the QMS housing has only a very small effect on QMS behaviour.