Measurement and Results - Internal standard selection for ICP-MS

For Al and the low mass alkali elements (e.g., Li, Na, and K) ⁶Li is a good choice (it is possible to measure Li using ⁷Li for quantification and ⁶Li for internal standardization). For alkaline earths such as Ca and Mg, as well as first row transition metals (Ti through ~Cu), Sc works well for almost any sample that isn’t rare-earth enriched. The ionization potential of Zn is similar to As, so if your solutions are chloride-free As could be a good choice for Zn. In the 80-120 mass range, Rh is probably the best choice based upon your analytes of interest. For Ba and the rare earths (La, Ce, and Nd), a good internal standard would be Tb, as it’s closer in ionization potential than Rh and a closer in mass. For the highest masses (Bi, Th, and U) Re is a good IS, as it avoids the precious metals like Au, which require some HCl for stability and that can tend to ‘stick’ in the sample introduction system.