The Limits of EPMA Accuracy

Probeman · April 27, 2026, 08:32:12 AM

Quote from: aducharme on April 27, 2026, 12:08:51 AM
Quote from: Probeman on April 20, 2026, 11:09:55 AMDo you want to "break" the EPMA 1% accuracy barrier? You need to make sure your PHA peaks are completely above the baseline level at the highest count rate you anticipate measuring and be in *integral* PHA mode.

Paul Carpenter, 2008: "Avoid tight PHA window, use integral mode unless a PHA interference is observed" and "Use integral mode unless PHA energy discrimination required" (https://epmalab.uoregon.edu/Workshop2/Carpenter_Oregon_Workshop_2007.pdf)

Nice find.

Yes, Paul has been saying this all along, but there's a critical component that I'm not seeing in his presentation.

For example, he says: "Low energy pulses must be discriminated from baseline noise. Need proper setting of noise threshold, baseline, and window settings of WDS pulse height analyzer."

And that is certainly true. But it would be better to merely say: make sure that the PHA peak is completely above the baseline level at the highest count rate that one intends to measure.

Then there is no need to perform "count rate matching" as he claims a bit later on: "Pulse energy shift with varying count rate results in instability. At high count rates pulses are poorly discriminated from baseline noise. Use similar count rates on standard and sample". I say we don't need to "count rate match" if we tune our PHAs properly...

Also, it's not "instability" that occurs with "pulse energy shift" or what I would call "pulse height depression". What occurs when the PHA peaks starts to shift lower (at higher count rates) or shifts higher (at lower count rates), is not "instability" but rather "non-linearity". This is exactly why people seem to think that they need to "count rate match" their standard and unknown, but it is simply not necessary as long as one sets their PHA gain or bias high enough so that the PHA peak is *completely* above the baseline level at the highest count rate that one expects to measure (usually the highest concentration (primary std) at the highest beam current to be utilized).

That is, as the PHA shifts higher or lower, the baseline either cuts off pulse counts or includes more pulse counts from the left side tail of the PHA peak, thus introducing a non-linear response as a function of count rate.

Paul then mentions this: "Avoid tight PHA window, use integral mode unless a PHA interference is observed." But I would modify this to say: Because the use of PHA differential mode does not help with same Bragg order interferences, instead allow all interferences (same or higher order) to be counted and deal with the interferences properly using the quantitative interference correction.

I say this because, even in the case of higher order interferences, one cannot be sure that the interference pulses are cleanly separated from the interfered pulses.

It is far better to obtain a linear response from our detectors/counting electronics and deal with any interference corrections in software. The one exception I can think of is maybe analyzing trace oxygen in a Na compound because it's difficult to find a material containing a known amount of Na but no oxygen, for use as an interference standard!

Probeman · April 27, 2026, 10:06:07 AM

Here's an example from a week ago where we analyzed PbSiO3 (natural Alamosite assumed stoichiometry) using SiO2 as the primary standard. Here are the results for all 11 matrix corrections:

Summary of All Calculated (averaged) Matrix Corrections:
St  386 Set   8 Alamosite (PbSiO3)
FFAST    Chantler (NIST v 2.1, 2005)

Elemental Weight Percents:
ELEM:       Si      Mg      Mn      Fe      Pb       O   TOTAL
     1  10.370   -.013   -.005    .011  73.151  16.939 100.454   Armstrong/Brown/Scott-Love (prZ)
     2   9.228   -.010   -.005    .011  73.151  16.939  99.314   Philibert/Duncumb-Reed
     3   9.691   -.011   -.005    .012  73.151  16.939  99.777   Heinrich/Duncumb-Reed
     4   9.302   -.011   -.005    .011  73.151  16.939  99.388   Love-Scott I
     5   9.423   -.011   -.005    .011  73.151  16.939  99.509   Love-Scott II
     6   8.037   -.010   -.004    .010  73.151  16.939  98.123   Packwood Phi(prZ) (EPQ-91)
     7  10.056   -.012   -.005    .012  73.151  16.939 100.141   Bastin (original) (prZ)
     8   9.481   -.011   -.005    .011  73.151  16.939  99.566   Bastin PROZA Phi (prZ) (EPQ-91)
     9   9.314   -.011   -.005    .011  73.151  16.939  99.399   Pouchou and Pichoir-Full (PAP)
    10   9.146   -.011   -.005    .011  73.151  16.939  99.232   Pouchou and Pichoir-Simplified (XPP)
    11   9.996   -.012   -.005    .011  73.151  16.939 100.080   Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:    9.459   -.011   -.005    .011  73.151  16.939  99.544
SDEV:     .612    .001    .000    .000    .000    .000    .612
SERR:     .185    .000    .000    .000    .000    .000

MIN:     8.037   -.013   -.005    .010  73.151  16.939  98.123
MAX:    10.370   -.010   -.004    .012  73.151  16.939 100.454

Percent Variances:
ELEM:       Si      Mg      Mn      Fe      Pb       O
PUBL:    9.910    n.a.    n.a.    n.a.  73.151  16.939
STDS:       14      12      25     395     ---     ---

ELEM:       Si      Mg      Mn      Fe      Pb       O
     1    4.65     ---     ---     ---     ---     ---           Armstrong/Brown/Scott-Love (prZ)
     2   -6.88     ---     ---     ---     ---     ---           Philibert/Duncumb-Reed
     3   -2.21     ---     ---     ---     ---     ---           Heinrich/Duncumb-Reed
     4   -6.13     ---     ---     ---     ---     ---           Love-Scott I
     5   -4.91     ---     ---     ---     ---     ---           Love-Scott II
     6  -18.90     ---     ---     ---     ---     ---           Packwood Phi(prZ) (EPQ-91)
     7    1.47     ---     ---     ---     ---     ---           Bastin (original) (prZ)
     8   -4.33     ---     ---     ---     ---     ---           Bastin PROZA Phi (prZ) (EPQ-91)
     9   -6.01     ---     ---     ---     ---     ---           Pouchou and Pichoir-Full (PAP)
    10   -7.71     ---     ---     ---     ---     ---           Pouchou and Pichoir-Simplified (XPP)
    11     .87     ---     ---     ---     ---     ---           Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:    -4.55     .00     .00     .00     .00     .00        
SDEV:     6.18     .00     .00     .00     .00     .00        
SERR:     1.86     .00     .00     .00     .00     .00        

MIN:    -18.90     .00     .00     .00     .00     .00        
MAX:      4.65     .00     .00     .00     .00     .00

That's pretty wild, right?

Note the magnitude of the atomic number correction (from DebugMode in PFE or CalcZAF), for the last data point:

SAMPLE: 2545, ITERATIONS: 3, Z-BAR: 48.30882

 ELEMENT  ABSCOR  FLUCOR  ZEDCOR  ZAFCOR STP-POW BKS-COR   F(x)u      Ec   Eo/Ec    MACs  STDNUM uZAF/sZAF
   Si ka  1.6104   .9949   .7741  1.2402   .6403  1.2089   .5346  1.8390 10.8755 1355.02      14    1.0382
   Mg ka  2.4771  1.0000   .7735  1.9161   .6260  1.2358   .3264  1.3050 15.3257 2742.98      12    1.3592
   Mn ka  1.1342  1.0000   .8759   .9935   .8040  1.0894   .8562  6.5390  3.0586 356.758      25    .95158
   Fe ka  1.1032   .9854   .8580   .9327   .7936  1.0811   .8833  7.1120  2.8121 289.657     395    .88853

 ELEMENT   K-RAW K-RATIO ELEMWT% OXIDWT% ATOMIC% FORMULA TAKEOFF KILOVOL                                        
   Si ka  .20530  .08033   9.962   -----  20.085    .000   40.00   20.00                                        
   Mg ka -.00019 -.00008   -.016   -----   -.037    .000   40.00   20.00                                        
   Mn ka -.00008 -.00006   -.006   -----   -.006    .000   40.00   20.00                                        
   Fe ka  .00024  .00016    .015   -----    .015    .000   40.00   20.00                                        
   Pb                     73.151   -----  19.993    .000
   O                      16.939   -----  59.950    .000
   TOTAL:                100.045   ----- 100.000    .000

And here for those interested are the analysis for all data points using the Armstrong/Donovan and Moy matrix correction:

St  386 Set   8 Alamosite (PbSiO3)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 30.0  Beam Size =   10
(Magnification (analytical) =  20000),        Beam Mode = Analog  Spot
(Magnification (default) =     1000, Magnification (imaging) =    100)
Image Shift (X,Y):                                         .00,    .00

Tsumeb, South West Africa
From Mineralogical Research, CA
(assumed stoichiometric)
Number of Data Lines:   6             Number of 'Good' Data Lines:   6
First/Last Date-Time: 04/19/2026 10:56:41 PM to 04/19/2026 11:08:42 PM

Average Total Oxygen:         .000     Average Total Weight%:  100.080
Average Calculated Oxygen:    .000     Z-Bar (Z Fraction^0.7):  48.289
Average Excess Oxygen:        .000     Average Atomic Weight:   56.630
Average ZAF Iteration:        3.00     Average Quant Iterate:     2.00

St  386 Set   8 Alamosite (PbSiO3), Results in Elemental Weight Percents
 
ELEM:       Si      Mg      Mn      Fe      Pb       O
TYPE:     ANAL    ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:      LIN     LIN     LIN     LIN
TIME:    60.00   60.00   60.00   60.00     ---     ---
BEAM:    29.88   29.88   29.88   29.88     ---     ---

ELEM:       Si      Mg      Mn      Fe      Pb       O   SUM  
  2540  10.013   -.014   -.001    .008  73.151  16.939 100.096
  2541  10.000   -.007   -.011    .011  73.151  16.939 100.083
  2542  10.020   -.009   -.001    .009  73.151  16.939 100.109
  2543  10.001   -.020   -.005    .009  73.151  16.939 100.074
  2544   9.982   -.009   -.003    .014  73.151  16.939 100.074
  2545   9.962   -.016   -.006    .015  73.151  16.939 100.045

AVER:    9.996   -.012   -.005    .011  73.151  16.939 100.080
SDEV:     .021    .005    .004    .003    .000    .000    .022
SERR:     .009    .002    .001    .001    .000    .000
%RSD:      .21  -38.89  -76.31   27.89     .00     .00

PUBL:    9.910    n.a.    n.a.    n.a.  73.151  16.939 100.000
%VAR:      .87     ---     ---     ---     ---     ---
DIFF:     .086     ---     ---     ---     ---     ---
STDS:       14      12      25     395     ---     ---

STKF:    .3913   .4276   .7418   .6867     ---     ---
STCT:  2304.52  745.26  466.57 1036.19     ---     ---

UNKF:    .0806  -.0001   .0000   .0001     ---     ---
UNCT:   474.75    -.11    -.03     .18     ---     ---
UNBG:    11.48    1.53    1.62    5.04     ---     ---

ZCOR:   1.2402  1.9158   .9936   .9328     ---     ---
KRAW:    .2060  -.0002  -.0001   .0002     ---     ---
PKBG:    42.37     .93     .98    1.04     ---     ---

Probeman · April 28, 2026, 09:36:43 AM

Here's your 1% EPMA accuracy from pure oxide primary standards post of the day!

Si Ka in albite using SiO2 as a primary standard:

Yes, this albite is a natural specimen, but it was assumed stoichiometric minus the traces... now here is Al Ka in the same albite, using Al2O3 as the primary standard:

This is good because Will Nachlas will probably be using a natural (alpine) albite from Julien Allaz for the FIGMAS standard mount. This albite might be the only natural mineral in the FIGMAS mount because there doesn't seem to be any synthetic (beam stable and water insoluble) Na minerals commercially available.

Unless anyone knows of something?

Probeman · April 30, 2026, 01:04:47 PM

Now let's look at accuracy when measuring Ti Ka extrapolating from TiO2 at 15 and 20 keV. Let's start with SrTiO3:

All points close to 1% relative accuracy! Now for RbTiOPO4 again at 15 and 20 keV:

Again, very close to 1% accuracy!

I'm sure many of you have synthetic TiO2 and SrTiO3 materials, and I'll bet a few of you have RbTiOPO4, which by the way can be obtained from Marc Schier for $100 a gram:

https://calchemist.com/

and makes a wonderful Rb standard and is completely beam stable. So what are you waiting for? Just be sure to tune your PHAs properly. Here's what Andrew and I used for these measurements:

Note that the PHA peak is completely above the baseline level. Yes, we had to amplify the detector a bit to get this accomplished, but with this gain/bias setting and in PHA integral mode, you will get 1% accuracy on suitable standards extrapolating from pure synthetic oxides!

Probeman · May 01, 2026, 11:38:15 AM

More "breaking the EPMA 1% accuracy barrier" of the day. Here's Si Ka measured in natural diopside (assumed stoichiometry minus traces) extrapolated from SiO2:

and here is Mg Ka extrapolated from the MgO primary std:

Wouldn't it be nice if every EPMA lab in the world were using the same synthetic SiO2, MgO, Fe3O4, TiO2, Al2O3, etc., primary standards? And we could check them against secondary standards such as synthetic MgAl2O4, Mg2SiO4, SrTiO3, etc?

That is exactly what Will Nachlas is working towards... hopefully he can give us an update on his global FIGMAS mount.

Quote from: wonachlas on November 22, 2021, 09:02:30 AMThe Focused Interest Group on MicroAnalytical Standards (FIGMAS), a FIG of the Microscopy Society of America (MSA) and co-sponsored by the Microanalysis Society (MAS), is organizing a series of round robin exercises to begin investigating synthetic standard materials for developing a universal standards mount and accompanying database of community k-ratios. Details of the round robin and a survey to express interest are included in the link below. All labs who meet the stated criteria are welcome to participate.

https://docs.google.com/forms/d/e/1FAIpQLSd8nttQYcex9UmnHJyD3iHE-vpL7gG5XVpNumX8-fqrWrgb9A/viewform

Probeman · May 05, 2026, 01:13:36 PM

Continuing with our "Limits of EPMA Accuracy" posts, here are analyses of NIST K-412 mineral glass analyzed using MgO and SiO2 as primary standards. First Mg Ka:

Around 1% accuracy extrapolating from pure oxide primary standards. Now for Si ka:

Better than 1% accuracy at both 15 and 20 keV!

This is doable using the constant k-ratio dead time calibrations, aligned spectrometers, properly tuned PHA settings, and the Donovan and Moy matrix correction with FFAST MACs!

Probeman · May 11, 2026, 03:03:33 PM

Following up with NIST SRM K-412 we have Fe Ka extrapolated from Fe3O4:

Again, ~1% relative accuracy. Now for Al Ka:

Now this is interesting. At 15 keV we are close, ~1% accuracy, but at 20 keV (in the middle) we are off by ~4%, though that's only an absolute difference of 0.2 wt%:

St  160 Set   2 NBS K-412 mineral glass
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 30.0  Beam Size =   10
(Magnification (analytical) =  20000),        Beam Mode = Analog  Spot
(Magnification (default) =     1000, Magnification (imaging) =    100)
Image Shift (X,Y):                                         .00,    .00

SRM 470, NIST
C.M. Taylor (Photometry?) FeO 2.77, Fe2O3 8.15
Total as FeO 10.10, Excess O 0.815
Na = 430 PPM (EPMA by JJD)
Number of Data Lines:   6             Number of 'Good' Data Lines:   6
First/Last Date-Time: 04/25/2026 05:36:42 PM to 04/25/2026 05:49:20 PM

Average Total Oxygen:         .000     Average Total Weight%:  100.253
Average Calculated Oxygen:    .000     Z-Bar (Z Fraction^0.7):  12.035
Average Excess Oxygen:        .000     Average Atomic Weight:   21.987
Average ZAF Iteration:        4.00     Average Quant Iterate:     2.00

St  160 Set   2 NBS K-412 mineral glass, Results in Elemental Weight Percents
 
ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC    SPEC
BGDS:      LIN     LIN     LIN     LIN     LIN
TIME:    60.00   60.00   60.00   60.00   60.00     ---     ---     ---
BEAM:    29.86   29.86   29.86   29.86   29.86     ---     ---     ---

ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O   SUM  
   721  21.176  11.703   7.790   5.115    .000  10.899    .077  43.597 100.357
   722  21.148  11.671   7.748   5.085   -.001  10.899    .077  43.597 100.224
   723  21.189  11.676   7.739   5.112    .008  10.899    .077  43.597 100.298
   724  21.158  11.712   7.773   5.086   -.002  10.899    .077  43.597 100.300
   725  21.130  11.661   7.699   5.122   -.003  10.899    .077  43.597 100.181
   726  21.100  11.646   7.712   5.117    .008  10.899    .077  43.597 100.157

AVER:   21.150  11.678   7.743   5.106    .002  10.899    .077  43.597 100.253
SDEV:     .032    .025    .035    .016    .005    .000    .000    .000    .078
SERR:     .013    .010    .014    .007    .002    .000    .000    .000
%RSD:      .15     .21     .45     .32  308.92     .00     .00     .00

PUBL:   21.199  11.657   7.742   4.906    n.a.  10.899    .077  43.597 100.077
%VAR:     -.23     .18     .02    4.08     ---     ---     ---     ---
DIFF:    -.049    .021    .001    .200     ---     ---     ---     ---
STDS:       14    3012     395    3013      22     ---     ---     ---

STKF:    .3913   .4281   .6867   .4056   .5626     ---     ---     ---
STCT:  2263.58  751.78 1072.35  948.82  169.10     ---     ---     ---

UNKF:    .1422   .0649   .0668   .0295   .0000     ---     ---     ---
UNCT:   822.93  114.02  104.35   69.05     .00     ---     ---     ---
UNBG:     4.41     .71    1.42     .92     .14     ---     ---     ---

ZCOR:   1.4869  1.7986  1.1589  1.7298  1.1913     ---     ---     ---
KRAW:    .3636   .1517   .0973   .0728   .0000     ---     ---     ---
PKBG:   187.44  160.90   74.60   75.86    1.03     ---     ---     ---

Interestingly all the matrix corrections are off for Al at 20 keV, some over and some under (except for Packwood, and then, all the other elements are off by 3 to 4%!):

Summary of All Calculated (averaged) Matrix Corrections:
St  160 Set   2 NBS K-412 mineral glass
FFAST    Chantler (NIST v 2.1, 2005)

Elemental Weight Percents:
ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O   TOTAL
     1  21.151  11.673   7.752   5.104    .002  10.899    .077  43.597 100.256   Armstrong/Brown/Scott-Love (prZ)
     2  21.127  11.461   7.940   5.065    .002  10.899    .077  43.597 100.167   Philibert/Duncumb-Reed
     3  21.222  11.591   7.680   5.110    .002  10.899    .077  43.597 100.178   Heinrich/Duncumb-Reed
     4  21.291  11.696   7.763   5.142    .002  10.899    .077  43.597 100.467   Love-Scott I
     5  21.213  11.714   7.760   5.128    .002  10.899    .077  43.597 100.390   Love-Scott II
     6  20.469  11.301   8.024   4.924    .002  10.899    .077  43.597  99.293   Packwood Phi(prZ) (EPQ-91)
     7  21.135  11.651   7.798   5.044    .002  10.899    .077  43.597 100.203   Bastin (original) (prZ)
     8  21.320  11.724   7.906   5.152    .002  10.899    .077  43.597 100.677   Bastin PROZA Phi (prZ) (EPQ-91)
     9  21.227  11.679   7.894   5.131    .002  10.899    .077  43.597 100.506   Pouchou and Pichoir-Full (PAP)
    10  21.066  11.586   7.905   5.077    .002  10.899    .077  43.597 100.209   Pouchou and Pichoir-Simplified (XPP)
    11  21.150  11.678   7.743   5.106    .002  10.899    .077  43.597 100.253   Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:   21.125  11.614   7.833   5.089    .002  10.899    .077  43.597 100.236
SDEV:     .230    .129    .106    .064    .000    .000    .000    .000    .353
SERR:     .069    .039    .032    .019    .000    .000    .000    .000

MIN:    20.469  11.301   7.680   4.924    .002  10.899    .077  43.597  99.293
MAX:    21.320  11.724   8.024   5.152    .002  10.899    .077  43.597 100.677

Percent Variances:
ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O
PUBL:   21.199  11.657   7.742   4.906    n.a.  10.899    .077  43.597
STDS:       14    3012     395    3013      22     ---     ---     ---

ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O
     1    -.23     .14     .14    4.03     ---     ---     ---     ---           Armstrong/Brown/Scott-Love (prZ)
     2    -.34   -1.68    2.56    3.24     ---     ---     ---     ---           Philibert/Duncumb-Reed
     3     .11    -.57    -.80    4.15     ---     ---     ---     ---           Heinrich/Duncumb-Reed
     4     .43     .34     .27    4.81     ---     ---     ---     ---           Love-Scott I
     5     .07     .49     .24    4.52     ---     ---     ---     ---           Love-Scott II
     6   -3.44   -3.06    3.65     .37     ---     ---     ---     ---           Packwood Phi(prZ) (EPQ-91)
     7    -.30    -.05     .73    2.82     ---     ---     ---     ---           Bastin (original) (prZ)
     8     .57     .58    2.12    5.01     ---     ---     ---     ---           Bastin PROZA Phi (prZ) (EPQ-91)
     9     .13     .19    1.97    4.58     ---     ---     ---     ---           Pouchou and Pichoir-Full (PAP)
    10    -.63    -.61    2.10    3.48     ---     ---     ---     ---           Pouchou and Pichoir-Simplified (XPP)
    11    -.23     .18     .02    4.08     ---     ---     ---     ---           Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:     -.35    -.37    1.18    3.74     .00     .00     .00     .00        
SDEV:     1.08    1.10    1.36    1.30     .00     .00     .00     .00        
SERR:      .33     .33     .41     .39     .00     .00     .00     .00        

MIN:     -3.44   -3.06    -.80     .37     .00     .00     .00     .00        
MAX:       .57     .58    3.65    5.01     .00     .00     .00     .00

The Fe result for the Donovan and Moy correction is also very impressive.

Looking at the 15 keV data, yes, Al is off by ~1.4% relative, but that's only a difference of 700 PPM!

St  160 Set   1 NBS K-412 mineral glass
TakeOff = 40.0  KiloVolt = 15.0  Beam Current = 30.0  Beam Size =   10
(Magnification (analytical) =  20000),        Beam Mode = Analog  Spot
(Magnification (default) =     1000, Magnification (imaging) =    100)
Image Shift (X,Y):                                         .00,    .00

SRM 470, NIST
C.M. Taylor (Photometry?) FeO 2.77, Fe2O3 8.15
Total as FeO 10.10, Excess O 0.815
Na = 430 PPM (EPMA by JJD)
Number of Data Lines:   6             Number of 'Good' Data Lines:   6
First/Last Date-Time: 04/25/2026 01:30:21 PM to 04/25/2026 01:42:59 PM

Average Total Oxygen:         .000     Average Total Weight%:  100.133
Average Calculated Oxygen:    .000     Z-Bar (Z Fraction^0.7):  12.033
Average Excess Oxygen:        .000     Average Atomic Weight:   21.981
Average ZAF Iteration:        4.00     Average Quant Iterate:     2.00

St  160 Set   1 NBS K-412 mineral glass, Results in Elemental Weight Percents
 
ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O
TYPE:     ANAL    ANAL    ANAL    ANAL    ANAL    SPEC    SPEC    SPEC
BGDS:      LIN     LIN     LIN     LIN     LIN
TIME:    60.00   60.00   60.00   60.00   60.00     ---     ---     ---
BEAM:    30.07   30.07   30.07   30.07   30.07     ---     ---     ---

ELEM:       Si      Mg      Fe      Al      Ti      Ca      Mn       O   SUM  
   625  21.314  11.603   7.704   4.999   -.006  10.899    .077  43.597 100.187
   626  21.295  11.556   7.679   4.950    .002  10.899    .077  43.597 100.055
   627  21.317  11.573   7.690   4.978    .005  10.899    .077  43.597 100.137
   628  21.343  11.616   7.697   5.013   -.004  10.899    .077  43.597 100.239
   629  21.287  11.542   7.723   4.937    .007  10.899    .077  43.597 100.069
   630  21.299  11.543   7.718   4.977   -.001  10.899    .077  43.597 100.110

AVER:   21.309  11.572   7.702   4.976    .001  10.899    .077  43.597 100.133
SDEV:     .020    .031    .017    .029    .005    .000    .000    .000    .071
SERR:     .008    .013    .007    .012    .002    .000    .000    .000
%RSD:      .09     .27     .22     .57  734.52     .00     .00     .00

PUBL:   21.199  11.657   7.742   4.906    n.a.  10.899    .077  43.597 100.077
%VAR:      .52    -.73    -.52    1.42     ---     ---     ---     ---
DIFF:     .110   -.085   -.040    .070     ---     ---     ---     ---
STDS:       14    3012     395    3013      22     ---     ---     ---

STKF:    .4129   .4791   .6790   .4399   .5564     ---     ---     ---
STCT:  1650.58  634.29  492.16  768.23   90.08     ---     ---     ---

UNKF:    .1648   .0783   .0654   .0344   .0000     ---     ---     ---
UNCT:   658.65  103.70   47.39   60.14     .00     ---     ---     ---
UNBG:     3.77     .63     .84     .83     .09     ---     ---     ---

ZCOR:   1.2934  1.4774  1.1781  1.4449  1.1800     ---     ---     ---
KRAW:    .3990   .1635   .0963   .0783   .0000     ---     ---     ---

Probeman · May 22, 2026, 02:05:41 PM

We reproduced the Mg and Si analyses in Mg2SiO4:

https://smf.probesoftware.com/index.php?topic=1831.msg14120#msg14120

and got very similar results as before:

for Mg Ka within 1% at both 15 and 20 keV, and for Si Ka within 1% for 15 keV, but only within 2% at 20 keV:

At 15 keV, both Armstrong/Brown matrix corrections do better than PAP:

Summary of All Calculated (averaged) Matrix Corrections:
St  273 Set   3 Mg2SiO4 (magnesium olivine) synthetic
FFAST    Chantler (NIST v 2.1, 2005)

Elemental Weight Percents:
ELEM:       Si      Mg      Fe      Al      Ti       O   TOTAL
     1  20.038  34.423    .004    .004    .004  45.486  99.959   Armstrong/Brown/Scott-Love (prZ)
     2  20.436  34.361    .004    .004    .005  45.486 100.295   Philibert/Duncumb-Reed
     3  20.324  34.509    .004    .004    .004  45.486 100.332   Heinrich/Duncumb-Reed
     4  20.149  34.444    .004    .004    .004  45.486 100.091   Love-Scott I
     5  20.028  34.413    .004    .004    .004  45.486  99.939   Love-Scott II
     6  19.929  34.315    .004    .004    .005  45.486  99.743   Packwood Phi(prZ) (EPQ-91)
     7  20.258  34.417    .004    .004    .004  45.486 100.173   Bastin (original) (prZ)
     8  20.410  34.513    .004    .004    .005  45.486 100.421   Bastin PROZA Phi (prZ) (EPQ-91)
     9  20.303  34.482    .004    .004    .005  45.486 100.284   Pouchou and Pichoir-Full (PAP)
    10  20.211  34.442    .004    .004    .005  45.486 100.152   Pouchou and Pichoir-Simplified (XPP)
    11  20.046  34.422    .004    .004    .004  45.486  99.967   Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:   20.194  34.431    .004    .004    .004  45.486 100.123
SDEV:     .169    .059    .000    .000    .000    .000    .205
SERR:     .051    .018    .000    .000    .000    .000

MIN:    19.929  34.315    .004    .004    .004  45.486  99.743
MAX:    20.436  34.513    .004    .004    .005  45.486 100.421

Percent Variances:
ELEM:       Si      Mg      Fe      Al      Ti       O
PUBL:   19.960  34.554    n.a.    n.a.    n.a.  45.486
STDS:       14    3012     395    3013      22     ---

ELEM:       Si      Mg      Fe      Al      Ti       O
     1     .39    -.38     ---     ---     ---     ---           Armstrong/Brown/Scott-Love (prZ)
     2    2.38    -.56     ---     ---     ---     ---           Philibert/Duncumb-Reed
     3    1.82    -.13     ---     ---     ---     ---           Heinrich/Duncumb-Reed
     4     .95    -.32     ---     ---     ---     ---           Love-Scott I
     5     .34    -.41     ---     ---     ---     ---           Love-Scott II
     6    -.15    -.69     ---     ---     ---     ---           Packwood Phi(prZ) (EPQ-91)
     7    1.49    -.40     ---     ---     ---     ---           Bastin (original) (prZ)
     8    2.25    -.12     ---     ---     ---     ---           Bastin PROZA Phi (prZ) (EPQ-91)
     9    1.72    -.21     ---     ---     ---     ---           Pouchou and Pichoir-Full (PAP)
    10    1.26    -.33     ---     ---     ---     ---           Pouchou and Pichoir-Simplified (XPP)
    11     .43    -.38     ---     ---     ---     ---           Armstrong/Donovan and Moy BSC/BKS (prZ)

But at 20 keV, both Armstrong methods seem to do a bit worse for Si Ka in Mg2SiO4:

Summary of All Calculated (averaged) Matrix Corrections:
St  273 Set   2 Mg2SiO4 (magnesium olivine) synthetic
FFAST    Chantler (NIST v 2.1, 2005)

Elemental Weight Percents:
ELEM:       Si      Mg      Fe      Al      Ti       O   TOTAL
     1  19.616  34.466    .003    .001   -.002  45.486  99.571   Armstrong/Brown/Scott-Love (prZ)
     2  19.831  34.359    .003    .001   -.002  45.486  99.678   Philibert/Duncumb-Reed
     3  19.740  34.499    .003    .001   -.002  45.486  99.727   Heinrich/Duncumb-Reed
     4  19.982  34.536    .003    .001   -.002  45.486 100.006   Love-Scott I
     5  19.762  34.505    .003    .001   -.002  45.486  99.755   Love-Scott II
     6  19.407  34.332    .003    .001   -.002  45.486  99.227   Packwood Phi(prZ) (EPQ-91)
     7  19.931  34.500    .003    .001   -.002  45.486  99.920   Bastin (original) (prZ)
     8  20.094  34.568    .003    .001   -.002  45.486 100.151   Bastin PROZA Phi (prZ) (EPQ-91)
     9  20.066  34.556    .003    .001   -.002  45.486 100.111   Pouchou and Pichoir-Full (PAP)
    10  19.833  34.483    .003    .001   -.002  45.486  99.804   Pouchou and Pichoir-Simplified (XPP)
    11  19.630  34.467    .003    .001   -.002  45.486  99.585   Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:   19.809  34.479    .003    .001   -.002  45.486  99.776
SDEV:     .208    .074    .000    .000    .000    .000    .268
SERR:     .063    .022    .000    .000    .000    .000

MIN:    19.407  34.332    .003    .001   -.002  45.486  99.227
MAX:    20.094  34.568    .003    .001   -.002  45.486 100.151

Percent Variances:
ELEM:       Si      Mg      Fe      Al      Ti       O
PUBL:   19.960  34.554    n.a.    n.a.    n.a.  45.486
STDS:       14    3012     395    3013      22     ---

ELEM:       Si      Mg      Fe      Al      Ti       O
     1   -1.72    -.25     ---     ---     ---     ---           Armstrong/Brown/Scott-Love (prZ)
     2    -.65    -.57     ---     ---     ---     ---           Philibert/Duncumb-Reed
     3   -1.10    -.16     ---     ---     ---     ---           Heinrich/Duncumb-Reed
     4     .11    -.05     ---     ---     ---     ---           Love-Scott I
     5    -.99    -.14     ---     ---     ---     ---           Love-Scott II
     6   -2.77    -.64     ---     ---     ---     ---           Packwood Phi(prZ) (EPQ-91)
     7    -.14    -.16     ---     ---     ---     ---           Bastin (original) (prZ)
     8     .67     .04     ---     ---     ---     ---           Bastin PROZA Phi (prZ) (EPQ-91)
     9     .53     .01     ---     ---     ---     ---           Pouchou and Pichoir-Full (PAP)
    10    -.64    -.21     ---     ---     ---     ---           Pouchou and Pichoir-Simplified (XPP)
    11   -1.66    -.25     ---     ---     ---     ---           Armstrong/Donovan and Moy BSC/BKS (prZ)

AVER:     -.76    -.22     .00     .00     .00     .00        
SDEV:     1.04     .21     .00     .00     .00     .00        
SERR:      .31     .06     .00     .00     .00     .00        

MIN:     -2.77    -.64     .00     .00     .00     .00        
MAX:       .67     .04     .00     .00     .00     .00

Though Mg Ka looks great.

Probeman · May 28, 2026, 01:49:23 PM

Re-running Mg Ka and Al Ka on our MgAl2O4 synthetic using MgO and Al2O3 as primary standards we obtain this for Mg Ka:

Both 15 and 20 (center) keV analyses are close to 1% relative accuracy. Here for Al Ka:

Again, close to 1% relative accuracy extrapolating from pure oxide primary standards.

Probeman · May 31, 2026, 10:03:05 AM

Here are the full set of analyses at 15 and 20 keV for the Si Ka in PbSiO3 extrapolated from SiO2 as the primary standard, I showed previously:

https://smf.probesoftware.com/index.php?topic=1831.msg14152#msg14152

It's interesting that the 15 keV analyses are all around ~1% low and the 20 keV analyses are all around 1% high.

Does that mean if we ran them again at 18 keV, they would be even better accuracy? I think I will try doing another run with a range of keVs and plotting accuracy vs keV when I get a chance!

John Donovan · June 03, 2026, 05:34:07 PM

Just a quick note that we've added a new menu under the Probe for EPMA Help menu on tuning PHA settings for best accuracy that links to a pdf:

Right now this pdf only has examples for Cameca EPMA instruments, so we would very much appreciate any screen captures of PHA scans for JEOL instruments tuned in a similar manner to the spec 3 LLIF at high currents.

Update PFE from the Help menu to see this most recent document.

AndrewLocock · June 04, 2026, 12:41:54 PM

The recent improvements in Probe-for-EPMA are impressive, particularly in the areas of matrix corrections, background fitting and the resultant accuracy.

However, I suggest that matrix matching, where possible can still provide slight improvements in accuracy.
As an example I provide actual average analyses of troilite, alabandite, and pyrite, using two different standards for the Fe and S - pyrrhotite (Fe7S8) and marcasite (FeS2).

(or attached PDF)

For troilite and alabandite, the Fe & S standard that gives the best results is pyrrhotite.
(Admittedly, the differences for alabandite are trivial).
Whereas for pyrite, the Fe & S standard that gives the best results is marcasite.
In these analyses, it is iron that is most affected by the choice of standard.
Because of this behavior, matrix matching for Fe is still an improvement in this system.

Cheers, Andrew

Probeman · June 04, 2026, 07:33:08 PM

Quote from: AndrewLocock on June 04, 2026, 12:41:54 PMThe recent improvements in Probe-for-EPMA are impressive, particularly in the areas of matrix corrections, background fitting and the resultant accuracy.

However, I suggest that matrix matching, where possible can still provide slight improvements in accuracy.

Thanks! It would also be nice to see some percent relative errors for these analyses...

Yes, I completely agree that "matrix matching" ones standard to ones unknown, can minimize the matrix correction. But the real problem I think that so called "matrix matching" is addressing is not really the matrix correction, but rather it is "count rate matching".

Because using a standard with a similar matrix means the concentrations are probably similar, and therefore the count rates are also similar. Therefore "count rate matching" also minimizes the dead time correction and makes pulse height depression less of an issue, so that helps when count rates differ between the standard and the unknown. This, I think, is the real reason many analysts are selecting a standard with a similar matrix to their unknown!

The other problem is whether the "matrix matched" standard one selects is actually what it is claimed to be. For example, is the assumed stoichiometry of pyrrhotite actually what it is? We know that the natural San Carlos olivine (even when sourced from the Smithsonian) has a significantly variable composition as reported by John Fournelle and others. Which we suspect explains why various EPMA labs around the world report reproducible intra-lab results, but consistently different inter-lab results (see Wieser et al, Barometers behaving badly, 2023). So much so that geologists have taken to creating laboratory "correction factors" for each lab! Is this really what we want?

https://smf.probesoftware.com/index.php?topic=1831.msg13974#msg13974

What we need are globally distributed high purity end member synthetic minerals, but also have our instrument well calibrated so they can handle standards and unknowns with very different count rates.

Look, I get it. If one performs the dead time, Bragg order k-ratio calibrations and the PHA integral-baseline tuning method I have suggested in this topic, one could use high purity synthetic MgO as a Mg Ka standard for analyzing olivines, but one could also use a high purity synthetic Mg2SiO4. And you know what? Both will be included in the FIGMAS mount that Will Nachlas is putting together with support from MAS. Because then we can measure k-ratio consensus (consensi?) between labs, once these mounts are distributed globally!

As stated above, the real reason I think that many users find "matrix matched" standards to be superior, is because they are actually "count rate matching" to their unknowns. Why is this? Because their dead time constants are not calibrated properly and they are not using the integral baseline PHA tuning method (described above) to obtain a linear response from their electronics. So they *have* to use "count rate matched" standards, even when we know they are heterogeneous from grain to grain.

Does anyone remember when Gene Jarosewich said that if you use the Smithsonian mineral standards you should average at least 10 grams for standardizing to obtain an accurate comparison to his wet chemistry? Does *anyone* do that? No, they use their "favorite" grain...

The more important question is, have they run the constant k-ratio dead time calibration method on their instruments? Probably not. See the pdf in the Help menu of Probe for EPMA and here:

https://smf.probesoftware.com/index.php?topic=1466.msg11102#msg11102

Have they checked their effective take off angles? (Though probably not a major issue for Fe ka!) See the pdf in the Help menu of Probe for EPMA and here:

https://smf.probesoftware.com/index.php?topic=1739.0

Also, have they tried the integral baseline PHA tuning method? Again see the pdf in the Help menu of the latest Probe for EPMA version as discussed in the post above. This integral baseline PHA tuning method allows one to have vastly different count rates between their standard and their unknown and still achieve ~1% relative accuracy. For example:

Yes, the new backscatter loss matrix correction method works really well, as do the FFAST MACs, but these are just part of the problem of why different labs are consistently reporting different results for the same materials and I think "matrix matched" heterogeneous natural standards is part of the problem.

Let's start with some k-ratio calibrations and get this sorted out by "failure" testing our instrument calibrations by extrapolating from a high purity synthetic primary standard to a much different secondary standard. Fe metal to pyrite might be good if we can assume the pyrite material is stoichiometric.

MgO to NIST glass is another good extrapolation... I've posted many other examples in this topic.

Probeman · June 10, 2026, 11:16:01 AM

Here's a plot of S Ka in ZnS using FeS2 as a primary standard over a range of keVs for three different analytical models:

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The Limits of EPMA Accuracy