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Chemical Stability and Compatibility - Stability of diluted standards

 
In our preparation for ICP-MS analysis of USP <232> elements, we perform an intermediate dilution of a 14 element blend. This is a 1:20 dilution to give concentrations (ug/mL, ppm) as follows: Cu = 65, Ni = 30, Mo = 9, V = 6, Cd = 0.25, Hg = 0.75, Pb = 0.25, As = 0.75, Ir = 5, Pd = 5, Pt = 5, Rh = 5, Ru = 5, Co = 2.5. I have viewed information at http://inorganicventures.com/stability-elements-ppb-concentration-levels, which has pointed me in the right direction and is the kind of information I’m looking for, except that our intermediate is at much greater concentrations. I am wondering if you can provide any information regarding the stability of this solution in a 5% nitric acid (HNO3), 1% hydrochloric acid (HCl) solution? If possible, I'm also interested in stability information for a 10 ug/L (ppb) mixture of In, Bi, 6-Li, Y, Sc, and Tb in 3% HNO3.
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Assuming the intermediate solution is stored in plastic, preparation in a 5% HNO3/1% HCl matrix should produce a stable solution for all elements except Hg. It’s possible that Hg will be stable, but our experience has been that in a HNO3 only matrix 0.75 ppm Hg will not be stable in a plastic container. Mercury at 0.75 ppm in a 10% HCl matrix is stable when stored in plastic, and it’s possible that the HNO3/HCl mixed matrix will enhance Hg stability, though we suggest performing a stability study to confirm this. Our website has more information regarding Hg stability in different matrices when stored in different container materials (http://www.inorganicventures.com/mercury-chemical-stability). Regarding In, Bi, 6Li, Y, Sc and Tb all at 10 ppb in 3% nitric acid, this solution should be chemically stable indefinitely.

Posted: 09/03/18 22:45:15

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