I have finally got around to mounting the Smithsonian REE phosphate standards, and am set to characterise the Pb levels of my chips next week. I have a question regarding this I was hoping someone could help me with. Do I need to do a full analysis of all major components of them using my current REE standards as the standardising material, or is it going to be an accurate enough Pb measurement if I use "Specified Concentrations" and input the certified #'s for the major components of each glass?
If I am reading it correctly (which I probably aren't), this is what Donovan et al. (2003) performed? But how does this work when some contain up to 1.7wt% Pb? Or is the matrix corrections when assuming stoichiometric REEPO4 relatively unaffected by this?
In addition, are the REE impurities in the orthophosphates of a high enough value to be concerned about? (ie do I need to quantify the REE impurities in addition to any Pb impurities).
Hi Ben,
Good questions and yes, you made me re-read my old Cand. Min. paper!
Because Pb is so variable in many of these Smithsonian orthophosphates, one only needs to determine the approximate value (at least in those materials where the Pb is significant). I say that only because I assume you are going to be using these as trace element standards for REEs in other materials? If so, whether the CePO4 has 2.2 or 2.3 wt% PbPO4 isn't going to affect the accuracy of the Ce value all that much. Remember, for trace elements the standard is not so important, but the background measurement is very important!
However, I did measure all the REEs in all the Smithsonian orthophosphates because, well, I was curious how pure their starting materials were. Remember, these orthophosphates were never intended for use as compositional standards- they were merely test materials for phosphor development and nuclear storage studies! Later on they were appropriated for use as REE compositional standard materials, but as we now know, they have their issues. But at the time, they were better than no REE standards at all!
Your main concerns will be with the accuracy of your background measurements- use shared off-peaks or MPB (multi-point backgrounds) and read the paper to see which REEs interfere with each other (assuming that some of your unknown samples have significant REEs that could cause such interferences).
The person who has done the most work on this is Karsten Goemann, so hopefully he will chime in here also.
john
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