Inductively coupled plasma mass spectrometry with a quadrupole mass filter operated in the third stability region

An inductively coupled plasma mass spectrometer system is described in which the quadrupole mass filter is operated in the third stability region with Mathieu parameters (a, q)=(3, 3). Operation at the upper tip of this region is found to give generally better sensitivity and resolution than operation at the lower tip. A limiting resolution at half height of 4000 at m/z 59 is possible with operation at the upper tip. This resolution is insufficient to separate atomic ions from molecular ions of the same nominal mass except in favorable cases. However, operation at moderate resolution (R _1/2=500 to 1000) is found to give very high abundance sensitivity (>10⁷). The results suggest that the third stability region may be advantageous for specialized applications of inductively coupled plasma mass spectrometry.