1.(Hg)
A common problem with Hg is stability. For an overview of Hg stability please our article entitled Mercury Stability Facts. In March of 2003, the EPA published a bulletin describing the use of Au to stabilize Hg solutions (www.epa.gov/nerlesd1/factsheets/mpt.pdf). When working at the ppb level we have found that using HCl rather than nitric acid will maintain the stability of Hg+2 solutions in plastic (LDPE) containers.
Another problem with Hg is loss during sample preparation. When performing acid digestions, the use of closed vessel digestion or the use of condensers should be considered. Ashing should be avoided. Only use validated sample preparation procedures.
Here are some additional suggestions when working with mercury:
The presence of reducing agents in the solution may reduce Hg to the metal causing false high results due to the volatility of the element where the introduction system delivers more Hg to the plasma as a result.
The use of plastic introduction systems will cause unusually long washout times. Glass is preferred and the use of HCl rather than nitric acid will reduce the washout time.
The use of nitric acid matrices for ppb Hg determinations by
ICP-MS should only be attempted using Au as a stabilizing agent (see above link).
2.Gold (Au)
The chemical stability of Au is very similar to that of Hg. The following suggestions may be helpful:
Nitric acid solutions of Au at the low ppm and ppb levels are not stable. Use HCl matrices.
Do no use Pt crucibles when ashing samples containing Au. Au will alloy with the Pt.
When measuring Au in the presence of significantly greater amounts of Pt using
ICP-MS, be aware of the resolving capability of your instrument.