Does Sn cause problems
The organizer of the seminar would like to add Sn to the list of elements that might cause problems……if you avoid the Alkaline or Rare Earths Elements then Sn should not be a problem…..or?
There are spectral issues with Sn by ICP-OES. The 189.926 nm line is the best with respect to sensitivity and freedom from spectral interference. I do not suggest using any of the other Sn lines because the spectral regions are 'dirty' with several elemental interference issues. In ICP-MS there issues. The MoO and U++ interfere with the 116 or 118 amu Sn masses. I suggest the 120 amu Sn line.
In addition, Sn is a problem element from two aspects: 1) The SnCl4 has a BP of 114°C causing a vaporization interference (i.e., more Sn gets into the plasma due to the vapor pressure). This is of concern if there is a significant amount of HCl present and the standards and samples do not have any HF (to fix the Sn) and different ratios of the Sn +2 and +4. 2) The second issue is the very problematic tendency of Sn to hydrolyze "out of solution" forming a semi-colloidal suspension. If the particulate is less than 8 microns (depending on nebulizer) you will get varying amounts of Sn in the plasma. The degree of hydrolysis is a function of Sn oxidation state, reagent order of addition, acid content, Sn concentration, and there is the complicating factor of the chemical form of the standard as well as the age of the sample digestate. Again, it is best to 'fix' the Sn by adding small amounts of HF.
Because of the need Sn has for HF stabilization the avoidance of elements that form insoluble fluorides such as the REE and Alkaline Earth elements as you pointed our above is important. In addition, elements forming water soluble fluoride complexes are trouble if they strip the fluoride from the Sn. Therefore, it is necessary to add excess HF to blends containing transition elements forming soluble fluorides otherwise the Sn will be stripped clean and undergo hydrolysis unless there is lots of acid present.
Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures & Fellow Chemist
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