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.

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.

That is a great paper! Thanks for sharing.

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.

https://xkcd.com/2755/

That's what happens when one includes the pharmaceutical sciences...