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Probe for EPMA / Re: Specifying Unanalyzed Elements For a Proper Matrix Correction
« Last post by Probeman on Today at 11:02:52 AM »Are there any proper correction procedures for situations where the sample mineral is porous? I am thinking of two cases: some serpentine minerals and chert. Obviously, you get low totals. You have the added problem that both phases can have significant water. I get asked very often can you just scale up the analysis to 100 and I constantly tell the users "no". But is there a correction procedure that can be applied? Thanks.
Great question. Anette's response is exactly on-point, so I can just mention a few random thoughts about porosity...
Porosity is a complicated subject. In the extreme porosity does not matter in (non-thin film) analysis EPMA as the distance between the atoms does not make a difference for the matrix corrections as long as the incident electrons come to rest inside the sample (interaction volume). And technically, for fully conductive samples where the porosity/voids are "filled" with vacuum, the porosity should also not make any difference.
However, problems with porosity begin to be a problem when the sample is not conductive and/or the voids are able to retain surface charging, and/or the voids are filled with some gas or liquid, and/or the voids are coated with adsorbed water, etc. Then Anette's suggestions are worth applying.
To answer your last question, yes, if we had a standard serpentinite that had the same exact porosity characteristics as our unknown, that could normalize out these effects, but of course that is not usually an option!

And regarding water, yes absolutely it should be included in the matrix correction! First to obtain an accurate matrix correction for the other elements which will be affected quite strongly by this "missing" water:
https://probesoftware.com/smf/index.php?topic=92.msg8485;topicseen#msg8485
In fact even a few wt% missing water can affect the matrix correction surprisingly enough as this hydrous glass analysis shows:
https://probesoftware.com/smf/index.php?topic=92.msg8439;topicseen#msg8439
See also:
Roman, D. C., Cashman, K. V., Gardner, C. A., Wallace, P. J., & Donovan, J. J. (2006). Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska. Bulletin of Volcanology, 68, 240-254.