SIMPLEX OPTIMIZATION OF NITROGEN ARGON PLASMAS IN INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY FOR THE REMOVAL OF CHLORIDE-BASED INTERFERENCES

In order to establish the effects of nitrogen addition to the coolant, auxiliary and nebulizer gas flows of an Ar plasma, polyatomic ions in a range of spiked and unspiked chloride reference materials (Rice Flour, Citrus Leaves, Dogfish Liver and Sea-water) and standard solution have been used. The response of a wide range of polyatomic ions was studied, with particular emphasis on the chlorine-based interferences ArCl+ and ClO+. Simplex optimization was used to optimize the operating parameters of the spectrometer in order to facilitate the maximum possible removal of the ArCl+ when using nitrogen addition. The ArCl+ interference is shown to be successfully removed with the addition of nitrogen to the coolant and nebulizer gas flows in the presence of 1 % chloride. Best results were obtained when 4.5% nitrogen was added to the nebulizer gas. These conditions have also greatly improved the determination of selenium and vanadium in the presence of chloride. In addition it has been found that nitrogen addition has some benefit in the reduction of MO+ and ArO+ interferences as well as the background response. The addition of nitrogen to the auxiliary gas offered little advantage for the removal of interference.