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

In this study, the sampling depth profiles of 19 elements in aqueous solution were obtained. The selected elements cover a wide range of atomic weights, ionization potentials, and oxide boiling points. The sampling position of maximum ICP-MS sensitivity of the elements depends on the boiling point of the corresponding oxide and the ionization potential of the elements. The boiling point determines the position in the ICP where significant vaporization of the dried aerosols occurs. In general, the peak position increases as the oxide boiling point of an element increases. However, the peak position for elements of high ionization potential and low oxide boiling point is downstream of the point of complete vaporization. The combined effect of analyte ionization potential and oxide boiling point on the optimized sampling position is illustrated by the linear plot of the difference in the temperature for significant ionization of an element and the boiling point of the corresponding oxide versus the oxide boiling point. The sampling depth profiles of single-particle ICP-MS of Au and ZrO₂ nanoparticles and the corresponding standard solution are of similar shape. The peak maximum of the sampling depth profiles shifts to a slightly higher position for the refractory ZrO₂ and large Au nanoparticles. The duration of particle vaporization for the nanoparticles becomes a significant factor in determining the peak position.