OPTIMIZATION STRATEGIES FOR THE REDUCTION OF NONSPECTROSCOPIC INTERFERENCES IN INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

Simplex optimization has been used to optimize ion lens conditions for a VG PlasmaQuad inductively coupled plasma mass spectrometer for the reduction of non-spectroscopic interferences due to a uranium matrix at a concentration of 10 000-mu-g g-1. The extraction lens voltage was shown to have the greatest effect on the extent of analyte signal suppression caused by the matrix. The use of a 0.4 mm orifice sampler (smaller than the 1.0 mm orifice sampler normally used) resulted in a large reduction in analyte suppression at all extraction lens voltages, whereas for the 1.0 mm and 0.7 mm orifice sampler a judicious choice of extraction lens voltage was necessary to ensure minimal analyte suppression. The main disadvantages of the 0.4 mm orifice sampler were the propensity for a secondary discharge to form in the orifice, resulting in elevated levels of doubly charged ions, and the tendency for the orifice to rapidly block in the presence of the 10 000-mu-g g-1 uranium matrix. A reduction in the expansion stage pressure also decreased the degree of analyte suppression in some experiments, although the effects were not reproducible from day to day.