The Limits of EPMA Accuracy

[Probeman]

Using the new plot option of relative percent variance (i.e., accuracy) in Probe for EPMA from the Output | Plot Standard and Unknown XY plots menu dialog:

https://smf.probesoftware.com/index.php?topic=40.msg14388#msg14388

we can quickly evaluate our secondary standard accuracy. Here for Mg Ka in MgAl2O4 using MgO as a primary standard in the FIGMAS mount from Will Nachlas:



All within 1% relative accuracy. But since we're plotting relative percent accuracy, we can plot more than a single compound, here Ti Ka in SrTiO3 and RbTiOPO4 using TiO2 as a primary standard:



And here for Fe ka in a multitude of compounds using Fe metal as the primary standard for the sulfides, and magnetite as a primary standard for the oxides, silicates and glasses:



Note that only the natural chromite is significantly outside the 1% variance accuracy limits.

[John Donovan]

In order to utilize the accuracy checks shown in the above plots, one must run their secondary standards as standard samples. Therefore, some of you have asked: how do I run my standards more than once?

Well first, to re-run ones standard samples a second time, just check the "Acquire Standard samples (again)" checkbox.  Even if you don't have an unknown sample selected, the standards will run a second time.

To run your standard even more replicates, just create a random unknown sample to run along with your standards and check the Re-Standardization Interval checkbox and enter a short interval (in hours) as seen here:



Say every hour or so. That's easy, right?

[Probeman]

With the new plotting feature in the Output | Output Standard and Unknown XY Plots menu dialog, we can plot relative accuracy for multiple elements:



We can see generally ~1% or better relative accuracy for Si, Mg and Fe. In addition we can plot the absolute wt% differences from the published values of the glasses here for Fe Ka:



Most of these Fe analyses are off by only a few hundred PPM!

[John Donovan]

In case anyone missed this post over the July 4th weekend, I wanted to call attention to this post:

https://smf.probesoftware.com/index.php?topic=8.msg14405#msg14405

For best EPMA accuracy, please set your defaults in the [software] section of your Probewin.ini file for the following items to these values:

[software]
DeadtimeCorrectionType=4    ; 1=traditional, 2=high precision formula, 3=Super Precision, 4=Logarithmic, 5=Exponential
MACTypeFlag=6               ; default MAC file (1 = LINEMU, 2 = CITZMU, 3 = McMaster, 4 = MAC30, 5 = MACJTA, 6 = FFAST
DefaultZAFType=11           ; default zaf algorithm 1=armprz, 2=pdrzaf, ... 9=papfull, 10=papsimp, 11=DAM

[John Donovan]

Andrew and I presented our poster yesterday at M&M 2026: "Breaking the EPMA1% Accuracy Barrier".

I've attached it below (login to see attachments). I am happy to discuss details with all, as some of the material is quite unintuitive. Feel free to call or email me.