Chemical Stability and Compatibility - High silver (Ag) recoveries using ICP-MS

A true increase in the concentration of only one element in a multi-element standard is possible only through contamination of some kind. Silver typically displays low values in older standards due to the introduction of chloride (often from HCl) during storage and preparation of the standard, so your observation of high Ag results are unusual. It's possible the new CCS-6 standard is contaminated with Cl and Ag in it is actually lower than the certified value, and therefore when you compare the old standards to it, your Ag results are high. Your historical signal intensities for Ag should allow you to quickly determine if this is a possibility; i.e., you should always expect roughly similar counts for a given concentration of Ag assuming machine performance, preparations/matrix, etc., are similar. Are your high Ag results observed for mixtures of the CCS group, or are they also present when you perform a direct comparison of only the old vs. new CCS-6 standard? As you are using ICP-MS, are both Ag isotopes (107 and 109) 40% high? If that is the case then it's possible that the standard was contaminated with Ag. If you are observing the discrepancy for mixtures of the CCS standards, a second possibility is that customers have reported high ICP-MS Ag results when the Ag standard is mixed with a second standard that contains HF (e.g., CCS-5). What exactly is occurring is not clear, but when the standards are not mixed, the issue of high Ag disappears. This could provide an option for testing if Ag truly is significantly higher in the older CCS-6 standard.