SIMPLEX OPTIMIZATION OF THE PLASMA PARAMETERS AND ION OPTICS OF AN INDUCTIVELY-COUPLED MASS-SPECTROMETER WITH PURE ARGON AND DOPED ARGON PLASMAS, USING A MULTIELEMENT FIGURE OF MERIT

A simplex procedure has been successfully applied to the optimization of both the plasma parameters and the ion optics of a commercial inductively coupled plasma mass spectrometry (ICP-MS) instrument for the maximization of SBRs for pneumatic nebulization. The objective function for the simplex was based on the signal to background ratios (SBRs) of 10 elements across the mass range with varying ionization efficiencies, to account for the various influences on ion transmission. This procedure has been applied to pure argon and molecular ps-doped-argon plasmas, to investigate the possible use of molecular gases as sensitivity enhancers. The simplex procedure successfully identified optimal operating conditions for maximum SBRs across the mass range, for the all argon and mixed gas plasmas. It was found, that simple manual tuning on the gross signal of a mid mass element did not result in a significant drop in SBRs and detection limits, compared to the simplex optimized conditions. Rigorous optimization of ICP-MS using pneumatic nebulization and the addition of molecular gases to the ICP, did not result in any significant improvements in SBRs and detection limits, when compared to the all argon system.