Chemical Stability and Compatibility - Aqua regia digests and silver (Ag) stability

Q: I have another question I was hoping you could help me out with. For my analytes that tend to have higher concentrations I am going to order single element standards at 1000 ppm for Sn, Cu, Ag, Pd and Zn. I want the highest concentration to be 250 ppm and the lowest to be 20 ppm. I digest most of my samples in Aqua Regia except Ag samples. I was wondering if I could have help coming up with a blend that is stable for varying concentrations?

A: If you wish to mix Sn, Cu, Ag, Pd and Zn you have two basic matrix options due to the presence of Ag: a HNO3/HF approach or a HCl matrix. If you choose the HNO3/HF approach, then we’d recommend the Sn and Pd products that are in HNO3/HF (Sn) and HNO3 (Pd). If you choose the strictly HCl approach, then you can avoid HF completely and we’d recommend Sn and Pd products that are both in HCl. Which brings us to Ag; silver can be stabilized in an excess of HCl and 250 ppm Ag will require ~50% (v/v) HCl, though the Ag will be photosensitive and the blend should be stored in the dark. Lower concentrations of Ag require less HCl, but we still recommend >30% HCl for concentrations of 50-100 ppm Ag, and 10% HCl for 10 ppm Ag. Depending upon which matrix approach you prefer, we can make specific recommendations for single-element products that would be most suitable.