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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.
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Thanks Anette,

I will take a look at the references you supplied.


Would the analysis still be valid, if the standard were the same mineral and porous, just as the unknown (chert standard and chert unknown), or am I degrading now the analysis, by compromising the standard? The porosity may not be the same in both, but would be closer.

Thanks.
Joe
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You may want to look into particle analyses by EPMA, specifically the peak-to-background ratio method. This is the usual recommendation to approaching quantitative analysis of porous samples. Otherwise, there are also recommendation to utilize standardless Monte Carlo simulations.

As per the Reed (2005) book: Another possibility is to measure peak-to-background ratios and make use of the fact that the effect of particle geometry on the continuum is similar to that on characteristic X-rays of the same energy (Statham and Pawley, 1977; Small, Newbury and Myklebust, 1979). Concentrations can be derived from peak-to-background ratios measured on the sample compared with ratios measured on standards. In ED spectra it is often necessary to remove the peaks by ‘stripping’ in order to determine the background, owing to the lack of suitable peak-free regions in the spectrum. The precision of measured peak to-background ratios is governed by the statistical error in the relatively low background intensity: this necessitates longer acquisition times than are customarily used for measuring peaks.

Some more references that may be relevant:
Goldstein, J.I., Newbury, D.E., Michael, J.R., Ritchie, N.W.M., Scott, J.H.J., Joy, D.C. (2018). Analysis of Specimens with Special Geometry: Irregular Bulk Objects and Particles. In: Scanning Electron Microscopy and X-Ray Microanalysis. Springer, New York, NY. https://doi.org/10.1007/978-1-4939-6676-9_23
Newbury, D. E. (2004). Quantitative electron probe microanalysis of rough targets: Testing the peak‐to‐local background method. Scanning: The Journal of Scanning Microscopies, 26(3), 103-114.
Sorbier, L., Rosenberg, E., & Merlet, C. (2004). Microanalysis of porous materials. Microscopy and Microanalysis, 10(6), 745-752.
Sorbier, L., Rosenberg, E., Merlet, C., & Llovet, X. (2000). EPMA of porous media: A Monte Carlo approach. Microchimica Acta, 132, 189-199.
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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.
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Probe Image / Re: No more rainbows!
« Last post by Anette von der Handt on March 30, 2023, 09:58:46 AM »
That is a great paper! Thanks for sharing.
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Probe for EPMA / Re: Blank Assignments
« Last post by Probeman on March 30, 2023, 05:33:02 AM »
If anyone has performed trace element analyses (e.g., ICP-MS) of the synthetic Mg2SiO4 materials obtained from either MTI or Oxide Corp (or any other commercial source for that matter!) I would be very interested to hear about the results.
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CalcZAF and Standard / Re: Nasty Boundary Fluorescence Analytical Situations
« Last post by John Donovan on March 29, 2023, 12:37:40 PM »
We found and fixed a small bug related to the oxygen-sulfur equivalence code implemented in v. 13.2.7 of Standard.exe and described here:

https://probesoftware.com/smf/index.php?topic=1247.msg11664#msg11664

which caused an error when calculating boundary fluorescence models for compounds containing sulfur. This error is now fixed.  If you have v. 13.2.7 of CalcZAF/Standard please use the Help | Update CalcZAF menu to update your CalcZAF/Standard applications.
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I am really enjoying this new book "Beyond Measure" which describes the history of measurement science.

https://www.amazon.com/Beyond-Measure-History-Measurement-Constants/dp/1324035854

Quote
A vibrant account of how measurement has invisibly shaped our world, from ancient civilizations to the modern day.

From the cubit to the kilogram, the humble inch to the speed of light, measurement is a powerful tool that humans invented to make sense of the world. In this revelatory work of science and social history, James Vincent dives into its hidden world, taking readers from ancient Egypt, where measuring the annual depth of the Nile was an essential task, to the intellectual origins of the metric system in the French Revolution, and from the surprisingly animated rivalry between metric and imperial, to our current age of the “quantified self.” At every turn, Vincent is keenly attuned to the political consequences of measurement, exploring how it has also been used as a tool for oppression and control.

Beyond Measure reveals how measurement is not only deeply entwined with our experience of the world, but also how its history encompasses and shapes the human quest for knowledge.
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Probe Software User Forum / Re: EPMA Humor
« Last post by Probeman on March 29, 2023, 05:10:55 AM »


https://xkcd.com/2755/

That's what happens when one includes the pharmaceutical sciences...   ;D
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Probe for EPMA / Re: Blank Assignments
« Last post by Probeman on March 29, 2023, 04:06:17 AM »
Had a question for you with respect to the idea of checking the zero concentrations on standard calibrations when doing trace elements to ensure your backgrounds are placed properly. Barring an overlap interference, would it matter which standard you used to check the zero concentration. In my case, where I have been measuring trace Al in olivine, could I use an Fe or Si metal standard, or some oxide standard, to check the zero concentration for Al, or do I have to use a synthetic, Al-free olivine? Obviously the matrix corrections will change, so I assume, whenever possible, use the same or similar mineral?

So yes, to answer your last question, I think for testing of trace accuracy in olivines it would be worth trying a zero blank of any Al-free silicate. For trace Al accuracy in olivines the main problem is the sloped (and curved) shape of the background at the Al Ka peak position on TAP due to the large nearby Si Ka peak.  See fig 3 in this paper:

Donovan, John J., Heather A. Lowers, and Brian G. Rusk. "Improved electron probe microanalysis of trace elements in quartz." American Mineralogist 96.2-3 (2011): 274-282.

So any high purity material containing Si and no Al would probably work fine. If you don't have a synthetic high purity olivine such as Mg2SiO4 maybe try SiO2. Note that synthetic Mg2SiO4 is available commercially and  think Will Nachlas has found sources for it.  The main problem with some of these synthetic materials is that they are intended for epitaxial crystal growth substrates, so they normally want to sell you oriented and polished material which of course isn't necessary for our use as microanalysis standards.

I would contact the vendors and see if they have "raw" material that they would be willing to provide to you.
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