INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY WITH A QUADRUPOLE MASS FILTER OPERATED IN THE 3RD STABILITY REGION

An inductively coupled plasma mass spectrometer system is described in which the quadrupole mass filter is operated in the third stability r egion with Mathieu parameters (a, q) approximate to (3, 3). Operation at the upper tip of this region is found to give generally better sens itivity and resolution than operation at the lower tip. A limiting res olution at half height of 4000 at m/z 59 is possible with operation at the upper tip. This resolution is insufficient to separate atomic ion s from molecular ions of the same nominal mass except in favorable cas es. However, operation at moderate resolution (R-1/2 = 500 to 1000) is found to give very high abundance sensitivity (>10(7)). The results s uggest that the third stability region may be advantageous for special ized applications of inductively coupled plasma mass spectrometry. (C) 1997 American Society for Mass Spectrometry.