Effects of ionization potential of an element and boiling point of the corresponding oxide on the sampling depth for maximum ICP-MS sensitivity

Abstract

We propose that the ICP-MS sampling position for maximum sensitivity of an element depends on the ionization potential of the element and the boiling point of corresponding oxide . The boiling point governs the position of the aerosol in the ICP where the vaporization starts. The ionization potential governs the degree of ionization of the element. The positions for high degree of vaporization and ionization may not coincide. The sampling position for maximum sensitivity of the element is determined by the process that is more energy-demanding. The process that is less energy-demanding, however, has a strong effect on the sampling depth profile. In this study, the positions for maximum sensitivity of 19 selected elements in the form of aqueous solution were determined. The vaporization process has insignificant effect on the position of maximum sensitivity. The main factor governing the position is the ionization. The shape of the sampling depth profiles depends on the difference in position for initial vaporization of the dried aerosols and significant ionization of the element, The position for maximum sensitivity of elements of high ionization potential but volatile dried aerosol is farther away from the initial vaporization position. The difference in positions is smaller for elements of low ionization potential and refractory dried particle. The above observation was applied to single-particle ICP-MS. The discrete particles are of particle size larger than the dried aerosols of standard solutions and may require more time for complete vaporization. It is interesting that the positions of maximum sensitivity for aqueous solution and discrete Au and ZrO2 nanoparticles were comparable. The findings may be used for the estimation of sampling position for maximum sensitivity for SP-ICP-MS using aqueous solutions. Acknowledgement: General Research Fund (GRF) project number 17300414