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Chemical Stability and Compatibility - Silver (Ag) stability in multi-element standards with chloride

 
I am having stability problems with Ag in my standards. I have primarily two sets of standards, one for testing sulfuric acid and one for testing lead-based materials (lead pastes and lead oxides). For my standards, I am using IV-ICPMS-71A, and adding Pt, Cl, Sb, Re, Bi, Te, and Sn. Standards are 1, 0.5, 0.1, and 0.01 ppm. I acidify the standards with 2.0% HNO3. In addition, the sulfuric acid standards have added 10,000 ppm H2SO4; the lead standards contain 10,000 ppm Pb added. I do not add Cl to the lead standard. The remainder of the standard is DI water. In any case, it seems like Ag is not stable in my standards. Sometimes they will fail Ag calibration immediately, and sometimes they will hold up for several hours to a day. Never more than one day. Can you suggest a way to make my standards more stable?
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The Ag present in IV-ICPMS-71A will not be stable in the presence of Cl (chloride), unless an excess of chloride is present (typically as HCl). For reference, a 10 ug/mL solution of Ag is stable in a minimum of 10% (v/v) HCl (please see http://inorganicventures.com/silver-chemical-stability for more information). If you eliminate Cl from your standard mixture (e.g., your Pb standards), please be aware that Pt (and other precious metals) can also cause Ag stability issues, as they often are prepared/stabilized in HCl. In other words, even though your final matrix is HNO3, trace chloride present from other elements can also create Ag stability issues. If you wish to measure Pt in the presence of Ag, and assuming no other sources of chloride are present, we do offer a chloride-free Pt product (CGPTNO31) that can be combined with Ag to produce a stable mixture in HNO3.

Posted: 09/03/18 21:51:38

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