Acids, mainly nitric, are used to stabilize metals in aqueous solution, and for leaching/decomposition of solid samples. In fact, most instrumental measurements are performed on dilute nitric acid; thus the purity requirements on this acid correspond to those on the water used.

For preparing samples and solutions, pro analysi is the lowest grade in use with respect to commercially available acids. This is a relatively high quality, the product being accompanied by a specification of maximum levels of elemental impurities. For the most demanding applications, however, pro analysi nitric acid is further purified in the laboratory by "sub-boiling distillation" in a quartz apparatus. Unlike in ordinary distillation, there is no boiling of the liquid in this technique but merely evaporation from the surface followed by condensation. In this way splashes and aerosols, which may contaminate the distillate, are avoided. Furthermore, less metal is released from the quartz compared to glass. The distilled acid is stored in teflon bottles.