Chemical Stability and Compatibility - Mercury (Hg) starting material and complexing Sb (antimony)

The Hg starting material should not matter as long as mercury is present in the same chemical form, ideally as Hg⁺². If mercury is present in different chemical forms then it can generate very different signal intensities in an ICP (OES or MS) even though the total Hg content is exactly the same between two solutions. What we have observed is that Hg⁺² in solution can reduce to Hg^o and generate anomalously high intensities as a result of increased nebulization efficiency, and that this reduction can occur slowly over time, i.e., as the solution ages its apparent Hg concentration increases. This effect can be counteracted by heating the solution with concentrated HNO3, which offers a relatively simple test for determining if this is occurring. As for Sb, it requires some complexing ligand and tartrate is the classic approach. Fluoride added as HF is also effective and we use both chemistries. Using chloride from HCl should also work, though we have not extensively studied various Sb-HCl ratios to determine how much HCl would be necessary for a given amount of Sb. However, we routinely prepare Sb standards sourced from both Sb-tartrate and Sb-HF concentrates in HCl and generally observe no stability issues.