Author Topic: Specifying Unanalyzed Elements For a Proper Matrix Correction (Read 51453 times)

John Donovan · « **Reply #105 on:** August 19, 2019, 04:13:36 PM »

OK, now on to Probe for EPMA. We think the implementation of the ferrous/ferric calculation (from Droop, 1987) is pretty good, but please download the latest version (12.7.1) and let us know what you think. The CalcZAF implementation is described here:

https://probesoftware.com/smf/index.php?topic=691.msg8592#msg8592

So let's take an example of hematite. Calculating all iron as FeO we get these results:

Un 3 Hematite, Results in Elemental Weight Percents ELEM: Fe O TYPE: ANAL CALC BGDS: LIN TIME: 10.00 --- BEAM: 30.00 --- ELEM: Fe O SUM 29 68.992 19.766 88.758 30 69.126 19.805 88.931 31 68.758 19.699 88.457 AVER: 68.959 19.757 88.715 SDEV: .186 .053 .240 SERR: .108 .031 %RSD: .27 .27 STDS: 39 --- STKF: .6810 --- STCT: 228.06 --- UNKF: .6566 --- UNCT: 219.89 --- UNBG: .48 --- ZCOR: 1.0503 --- KRAW: .9642 --- PKBG: 456.58 --- Un 3 Hematite, Results in Oxide Weight Percents ELEM: FeO O SUM 29 88.758 .000 88.758 30 88.931 .000 88.931 31 88.457 .000 88.457 AVER: 88.715 .000 88.715 SDEV: .240 .000 .240 SERR: .138 .000 %RSD: .27 -91.65 STDS: 39 ---
Note the low totals (~88%) due to the missing ferric oxygen. Now we specify the ferrous/ferric calculation and the mineral cations and oxygen (2 and 3 respectively for hematites) as seen here:

and re-calculating we now obtain these results:

Un 3 Hematite, Results in Elemental Weight Percents ELEM: Fe O TYPE: ANAL CALC BGDS: LIN TIME: 10.00 --- BEAM: 30.00 --- ELEM: Fe O SUM 29 70.168 30.155 100.323 30 70.305 30.213 100.518 31 69.930 30.052 99.982 AVER: 70.134 30.140 100.274 SDEV: .190 .081 .271 SERR: .109 .047 %RSD: .27 .27 STDS: 39 --- STKF: .6810 --- STCT: 228.06 --- UNKF: .6566 --- UNCT: 219.89 --- UNBG: .48 --- ZCOR: 1.0682 --- KRAW: .9642 --- PKBG: 456.58 --- Ferrous/Ferric Calculation Results: Ferric/TotalFe FeO Fe2O3 Oxygen from Fe2O3 29 1.000 .000 100.323 10.052 30 1.000 .000 100.518 10.071 31 1.000 .000 99.982 10.017 AVER: 1.000 .000 100.274 10.047 Un 3 Hematite, Results in Oxide Weight Percents ELEM: FeO O SUM 29 90.271 10.052 100.323 30 90.447 10.071 100.518 31 89.965 10.017 99.982 AVER: 90.228 10.047 100.274 SDEV: .244 .027 .271 SERR: .141 .016 %RSD: .27 .27 STDS: 39 ---
Our totals are now much better but because we included this excess oxygen in the matrix correction as suggested by Brian Joy, even more impressive is that our Fe went from 68.959 to 70.134 wt%!

We also added this ferrous/ferric output to the User Specified Output options as seen here:

so now these results can be output to Excel as usual:

Probeman · « **Reply #106 on:** September 11, 2019, 02:38:22 PM »

Here's a "real world" example of a titanium magnetite with the ferrous/ferric excess oxygen calculation in Probe for EPMA using the method of Droop (1987) to calculate the excess oxygen from ferric iron. This excess oxygen is then added into the matrix correction for improved accuracy. The output below also includes oxides and sum of cations also as specified in the Calculation Options dialog.

Un 30 8400 Mgt Trav In-Out TakeOff = 40.0 KiloVolt = 15.0 Beam Current = 50.0 Beam Size = 0 (Magnification (analytical) = 20000), Beam Mode = Analog Spot (Magnification (default) = 1000, Magnification (imaging) = 100) Image Shift (X,Y): -2.00, 3.00 Formula Based on Sum of Cations = 3.00 Oxygen Calc. by Stoichiometry Number of Data Lines: 6 Number of 'Good' Data Lines: 6 First/Last Date-Time: 07/23/2019 02:12:20 PM to 07/23/2019 02:29:56 PM Average Total Oxygen: 28.684 Average Total Weight%: 100.294 Average Calculated Oxygen: 28.684 Average Atomic Number: 20.135 Average Excess Oxygen: .000 Average Atomic Weight: 31.696 Average ZAF Iteration: 3.00 Average Quant Iterate: 4.00 Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction Excess Oxygen From Ferric Iron Calculated and Included in the Matrix Correction Charge Balance Method of Droop (1987), Total Cations= 3.00, Total Oxygens= 4.00 Un 30 8400 Mgt Trav In-Out, Results in Elemental Weight Percents ELEM: Fe Mg Si Ti V Mn Cr Al O TYPE: ANAL ANAL ANAL ANAL ANAL ANAL ANAL ANAL CALC BGDS: MAN MAN MAN MAN LIN LIN MAN MAN TIME: 40.00 140.00 40.00 80.00 30.00 30.00 88.00 141.00 --- BEAM: 50.32 50.32 50.32 50.32 50.32 50.32 50.32 50.32 --- ELEM: Fe Mg Si Ti V Mn Cr Al O SUM 72 60.751 1.862 .019 6.903 .309 .403 .054 1.270 28.664 100.234 73 60.644 1.863 .075 6.872 .333 .407 .059 1.258 28.657 100.170 74 60.946 1.871 .021 6.884 .295 .405 .056 1.255 28.732 100.464 75 60.505 1.856 .028 6.918 .323 .420 .056 1.260 28.584 99.950 76 60.954 1.876 .016 6.951 .335 .422 .043 1.251 28.776 100.623 77 60.805 1.858 .023 6.949 .301 .404 .044 1.249 28.693 100.325 AVER: 60.768 1.864 .030 6.913 .316 .410 .052 1.257 28.684 100.294 SDEV: .175 .008 .022 .032 .017 .008 .007 .008 .066 .235 SERR: .071 .003 .009 .013 .007 .003 .003 .003 .027 %RSD: .29 .41 73.90 .47 5.40 2.06 12.65 .61 .23 STDS: 395 12 14 22 23 25 24 396 --- STKF: .6779 .4736 .4101 .5547 .6328 .7341 .6400 .0469 --- STCT: 6812.2 53482.2 7089.5 14540.1 13304.5 22081.3 4697.4 3264.8 --- UNKF: .5649 .0085 .0002 .0703 .0033 .0038 .0006 .0072 --- UNCT: 5676.3 964.8 3.7 1841.7 69.6 114.7 4.3 503.0 --- UNBG: 20.5 79.1 5.5 52.0 25.2 49.5 9.6 48.0 --- ZCOR: 1.0758 2.1821 1.4034 .9839 .9547 1.0761 .8885 1.7401 --- KRAW: .8333 .0180 .0005 .1267 .0052 .0052 .0009 .1541 --- PKBG: 277.35 13.19 1.68 36.42 3.77 3.32 1.45 11.48 --- INT%: .00 ---- ---- ---- -17.39 -.03 -10.90 .00 --- Ferrous/Ferric Calculation Results: Ferric/TotalFe FeO Fe2O3 Oxygen from Fe2O3 72 .458 42.390 39.749 3.983 73 .455 42.482 39.494 3.957 74 .460 42.324 40.100 4.018 75 .456 42.333 39.459 3.954 76 .458 42.468 39.953 4.003 77 .458 42.388 39.828 3.990 AVER: .458 42.397 39.764 3.984 Un 30 8400 Mgt Trav In-Out, Results in Oxide Weight Percents ELEM: FeO MgO SiO2 TiO2 V2O3 MnO Cr2O3 Al2O3 O SUM 72 78.156 3.087 .041 11.515 .454 .520 .079 2.400 3.983 100.234 73 78.019 3.090 .161 11.464 .491 .526 .086 2.377 3.957 100.170 74 78.407 3.103 .044 11.484 .433 .523 .081 2.371 4.018 100.464 75 77.839 3.078 .059 11.539 .476 .542 .082 2.382 3.954 99.950 76 78.418 3.110 .034 11.594 .492 .545 .063 2.363 4.003 100.623 77 78.225 3.080 .050 11.591 .442 .522 .065 2.359 3.990 100.325 AVER: 78.177 3.091 .065 11.531 .465 .530 .076 2.375 3.984 100.294 SDEV: .225 .013 .048 .054 .025 .011 .010 .015 .025 .235 SERR: .092 .005 .020 .022 .010 .004 .004 .006 .010 %RSD: .29 .41 73.90 .47 5.40 2.06 12.65 .61 .64 STDS: 395 12 14 22 23 25 24 396 --- Un 30 8400 Mgt Trav In-Out, Results Based on Sum of 3 Cations ELEM: Fe Mg Si Ti V Mn Cr Al O SUM 72 2.381 .168 .001 .315 .013 .016 .002 .103 3.921 6.921 73 2.377 .168 .006 .314 .014 .016 .002 .102 3.921 6.921 74 2.384 .168 .002 .314 .013 .016 .002 .102 3.922 6.922 75 2.378 .168 .002 .317 .014 .017 .002 .103 3.921 6.921 76 2.380 .168 .001 .316 .014 .017 .002 .101 3.922 6.922 77 2.382 .167 .002 .317 .013 .016 .002 .101 3.923 6.923 AVER: 2.380 .168 .002 .316 .014 .016 .002 .102 3.922 6.922 SDEV: .002 .000 .002 .001 .001 .000 .000 .001 .001 .001 SERR: .001 .000 .001 .001 .000 .000 .000 .000 .000 %RSD: .10 .24 73.96 .46 5.41 2.06 12.76 .74 .02
Note that if we did *not* include the calculation of excess oxygen in the matrix correction our oxides and formula would look like this:

Un 30 8400 Mgt Trav In-Out, Results in Oxide Weight Percents ELEM: FeO MgO SiO2 TiO2 V2O3 MnO Cr2O3 Al2O3 O SUM 72 77.687 3.107 .037 11.434 .451 .517 .074 2.412 .000 95.718 73 77.554 3.109 .158 11.383 .487 .523 .080 2.388 .000 95.684 74 77.933 3.123 .041 11.402 .430 .520 .076 2.383 .000 95.908 75 77.374 3.098 .056 11.458 .472 .539 .076 2.393 .000 95.467 76 77.946 3.130 .031 11.512 .489 .542 .058 2.375 .000 96.083 77 77.755 3.100 .047 11.509 .439 .519 .059 2.371 .000 95.799 AVER: 77.708 3.111 .062 11.450 .461 .527 .071 2.387 .000 95.776 SDEV: .221 .013 .048 .054 .025 .011 .010 .015 .000 .210 SERR: .090 .005 .020 .022 .010 .004 .004 .006 .000 %RSD: .28 .41 78.00 .47 5.41 2.06 13.52 .61 -167.33 STDS: 395 12 14 22 23 25 24 396 --- Un 30 8400 Mgt Trav In-Out, Results Based on Sum of 3 Cations ELEM: Fe Mg Si Ti V Mn Cr Al O SUM 72 2.379 .170 .001 .315 .013 .016 .002 .104 3.376 6.376 73 2.375 .170 .006 .313 .014 .016 .002 .103 3.379 6.379 74 2.382 .170 .002 .313 .013 .016 .002 .103 3.374 6.374 75 2.376 .170 .002 .316 .014 .017 .002 .104 3.378 6.378 76 2.378 .170 .001 .316 .014 .017 .002 .102 3.376 6.376 77 2.380 .169 .002 .317 .013 .016 .002 .102 3.377 6.377 AVER: 2.378 .170 .002 .315 .014 .016 .002 .103 3.377 6.377 SDEV: .002 .000 .002 .001 .001 .000 .000 .001 .002 .002 SERR: .001 .000 .001 .001 .000 .000 .000 .000 .001 %RSD: .10 .24 78.05 .46 5.41 2.06 13.63 .74 .06
Of course the oxygen formula is low, but note the effect of this "missing oxygen" on the concentrations of the other elements. E.g., without the excess oxygen in the matrix correction, the Fe and Ti concentrations went down, but the Mg and Al concentrations went up!

Probeman · « **Reply #107 on:** February 10, 2020, 10:14:23 PM »

Mike Dungan, Andrew Locock and I fixed a problem with some oxide compositions in the ferric/ferric excess oxygen calculation as seen here:

Ferrous/Ferric Calculation Results: Ferric/TotalFe FeO Fe2O3 Oxygen from Fe2O3 37 .387 44.824 31.498 3.156 38 .387 44.633 31.339 3.140 AVER: .387 44.729 31.419 3.148 Un 6 CH-19_Ox99_Mgt Core-1, Results in Oxide Weight Percents ELEM: FeO MgO TiO2 V2O3 MnO Cr2O3 Al2O3 SiO2 CaO O SUM 37 73.166 2.152 18.583 .543 .586 .006 1.835 .053 .014 3.156 100.093 38 72.832 2.159 18.500 .553 .574 .002 1.906 .043 .014 3.140 99.723 AVER: 72.999 2.156 18.541 .548 .580 .004 1.870 .048 .014 3.148 99.908 SDEV: .236 .005 .059 .008 .008 .003 .051 .007 .000 .011 .261 SERR: .167 .003 .042 .005 .006 .002 .036 .005 .000 .008 %RSD: .32 .23 .32 1.39 1.45 69.25 2.70 14.77 1.72 .36 STDS: 395 12 22 23 25 24 306 14 306 --- Un 6 CH-19_Ox99_Mgt Core-1, Results Based on Sum of 3 Cations ELEM: Fe Mg Ti V Mn Cr Al Si Ca O SUM 37 2.251 .118 .514 .016 .018 .000 .080 .002 .001 4.000 7.000 38 2.248 .119 .514 .016 .018 .000 .083 .002 .001 4.000 7.000 AVER: 2.250 .118 .514 .016 .018 .000 .081 .002 .001 4.000 7.000 SDEV: .002 .001 .000 .000 .000 .000 .002 .000 .000 .000 .000 SERR: .002 .000 .000 .000 .000 .000 .002 .000 .000 .000 %RSD: .10 .46 .09 1.62 1.22 69.07 2.93 14.55 1.49 .00
This change now properly handles oxides such as Al2O3, V2O3, Cr2O3, etc. You can update PFE anytime.

John Donovan · « **Reply #108 on:** June 29, 2020, 09:34:18 AM »

We've recently been working with Julien Allaz to fix the way in which the oxygen-halogen correction is applied to standards in Probe for EPMA as first reported by Ben Wade:

https://probesoftware.com/smf/index.php?topic=1247.msg9305#msg9305

During that time we realized that these recent halogen correction issues for standards (when oxygen is calculated by stoichiometry rather than a fixed concentration), are somewhat similar to the excess oxygen calculation using the Droop method of charge balance (hey- it's all about charge balance!). Again only for standard samples, when oxygen is calculated by stoichiometry (as opposed to added by fixed concentration from the standard database).

Previously, for the excess oxygen from ferric iron calculation, we simply did not allow one to perform this excess oxygen calculation for standards (only for unknown samples). But we realized yesterday that it's the same issue in that a double correction is applied for standards if the excess (or deficit) oxygen is already included in the standard database, and the excess (or deficit) oxygen correction for ferric oxygen (or halogen equivalence) is applied in Probe for EPMA, *and* the oxygen in the standard is calculated by stocihiometry. Whew!

So what we did was enable the calculation of excess oxygen for standards (just as we have had for the halogen correction), so if the standard analysis is using the default fixed oxygen concentration from the standard database, all is well. This can be seen is this output:

Excess Oxygen From Ferric Iron was not Included in the Matrix Correction (because oxygen was not calculated by cation stoichiometry) St 395 Set 1 Magnetite U.C. #3380, Results in Elemental Weight Percents ELEM: F Fe Al Mg Mn O TYPE: ANAL ANAL SPEC SPEC SPEC SPEC BGDS: LIN LIN TIME: 20.00 20.00 --- --- --- --- BEAM: 29.98 29.98 --- --- --- --- ELEM: F Fe Al Mg Mn O SUM 10 .051 71.844 .201 .072 .054 27.803 100.025 11 .073 72.195 .201 .072 .054 27.803 100.398 12 .026 72.209 .201 .072 .054 27.803 100.365 AVER: .050 72.083 .201 .072 .054 27.803 100.263 SDEV: .023 .207 .000 .000 .000 .000 .207 SERR: .014 .119 .000 .000 .000 .000 %RSD: 46.70 .29 .00 .00 .00 .00 PUBL: n.a. 72.080 .201 .072 .054 27.803 100.210 %VAR: --- (.00) .00 .00 .00 .00 DIFF: --- (.00) .000 .000 .000 .000 STDS: 835 395 --- --- --- --- STKF: .1715 .6779 --- --- --- --- STCT: 57.18 228.22 --- --- --- --- UNKF: .0002 .6779 --- --- --- --- UNCT: .07 228.22 --- --- --- --- UNBG: .32 .49 --- --- --- --- ZCOR: 2.2854 1.0633 --- --- --- --- KRAW: .0013 1.0000 --- --- --- --- PKBG: 1.23 466.16 --- --- --- --- Ferrous/Ferric Calculation Results: Ferric/TotalFe FeO Fe2O3 Oxygen from Fe2O3 10 .000 .000 .000 .000 11 .000 .000 .000 .000 12 .000 .000 .000 .000 AVER: .000 .000 .000 .000
But in the case where the user changes the standard analysis calculation to calculate oxygen by stoichiometry, the program will now zero out the excess oxygen (just as it now does for the deficit oxygen from halogens), and not perform a double correction as seen here:

Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction Oxygen Equivalent from Halogens (F/Cl/Br/I) was Subtracted in the Matrix Correction Excess Oxygen From Ferric Iron Calculated and Included in the Matrix Correction Charge Balance Method of Droop (1987), Total Cations= 3.00, Total Oxygens= 4.00 St 395 Set 1 Magnetite U.C. #3380, Results in Elemental Weight Percents ELEM: F Fe Al Mg Mn O TYPE: ANAL ANAL SPEC SPEC SPEC CALC BGDS: LIN LIN TIME: 20.00 20.00 --- --- --- --- BEAM: 29.98 29.98 --- --- --- --- ELEM: F Fe Al Mg Mn O SUM 10 .051 71.838 .201 .072 .054 27.742 99.957 11 .073 72.206 .201 .072 .054 27.908 100.514 12 .026 72.215 .201 .072 .054 27.859 100.427 AVER: .050 72.086 .201 .072 .054 27.836 100.299 SDEV: .023 .215 .000 .000 .000 .085 .300 SERR: .014 .124 .000 .000 .000 .049 %RSD: 46.75 .30 .00 .00 .00 .31 PUBL: n.a. 72.080 .201 .072 .054 27.803 100.210 %VAR: --- (.01) .00 .00 .00 .12 DIFF: --- (.01) .000 .000 .000 .033 STDS: 835 395 --- --- --- --- STKF: .1715 .6779 --- --- --- --- STCT: 57.18 228.22 --- --- --- --- UNKF: .0002 .6779 --- --- --- --- UNCT: .07 228.22 --- --- --- --- UNBG: .32 .49 --- --- --- --- ZCOR: 2.2865 1.0633 --- --- --- --- KRAW: .0013 1.0000 --- --- --- --- PKBG: 1.23 466.16 --- --- --- --- Ferrous/Ferric Calculation Results: Ferric/TotalFe FeO Fe2O3 Oxygen from Fe2O3 10 .674 30.092 69.266 6.940 11 .678 29.937 69.966 7.010 12 .671 30.591 69.252 6.938 AVER: .674 30.207 69.495 6.963

So now, the code for dealing with this is seen here:

Code: [Select]

If sample(1).Type% = 1 Then
analysis.WtPercents!(chan%) = ConvertTotalToExcessOxygen!(Int(1), sample(), stdsample())
If UseOxygenFromHalogensCorrectionFlag And sample(1).OxideOrElemental% = 1 Then
If analysis.WtPercents!(chan%) < 0# Then analysis.WtPercents!(chan%) = 0#  ' zero out oxygen deficit from standard database
End If
If sample(1).FerrousFerricCalculationFlag And sample(1).OxideOrElemental% = 1 Then
If analysis.WtPercents!(chan%) > 0# Then analysis.WtPercents!(chan%) = 0#  ' zero out oxygen excess from standard database
End If

' For unknowns, use specified oxygen weight percent
Else
analysis.WtPercents!(chan%) = stdsample(1).ElmPercents!(ip%)
End If

One possible remaining issue is when one has both halogens and ferric iron present in a standard, and one tries to calculate oxygen by stoichiometry, the excess/deficit oxygen might not be handled perfectly. In this case, we would just say, simply use the default to calculate oxygen elementally (fixed concentration from the standard database) and all will be well. But I think it will work, because if both the oxygen-halogen correction *and* the ferric iron calculation correction are turned on, you'll get a zero value for excess/deficit oxygen, so it should all work.

Remember, in all cases, the calculations for unknown samples are handled just fine. This is all pretty complicated we know, but please ask us any questions you may have.

In the meantime, update Probe for EPMA from the Help menu and these options are all available now.

John Donovan · « **Reply #109 on:** August 27, 2021, 08:19:43 AM »

Recently Andrew Locock found a mineral calculation for an unanalyzed elements situation which did not properly apply the oxygen-halogen correction when calculating oxygen by stoichiometry (that is, when not measuring oxygen, or specifying oxygen as a fixed concentration). The following examples were all measured by Andrew on one of his microprobe instruments (yes he has two of them!).

I should also mention that a full paper on the effects of unanalyzed elements in EPMA analysis is being prepared with Aurelien Moy as first author (and Andrew and myself and several others) that will be submitted later this year for publication.

As a quick review of the unanalyzed element problem can be seen is this carbonate example where oxygen is calculated by stoichiometry and carbon is calculated relative to stoichiometric oxygen in the ratio of 0.333 atoms of carbon to one atom of oxygen:

One can click on the images to see them better, though I'm not quite sure why he specified 0.33368 atoms of carbon in this example...

Another slightly more complicated example is that of tourmaline where 0.129 atoms of hydrogen are calculated relative to stoichiometric oxygen *and* 0.5 atoms of boron are calculated relative to silicon:

Now as for the halogen-oxygen correction, this is applied when oxygen is calculated by stoichiometry and a halogen element (chlorine, fluorine, etc.) is also present and replacing some of the stoichiometric oxygen. In these cases, unless a correction is applied to the stoichiometric oxygen concentration, too much oxygen will be included in the EPMA matrix iteration and the correction of the other elements will be calculated incorrectly.

For chlorine measurements the effect of this excess oxygen is fairly small, but for fluorine, which is heavily absorbed by oxygen, the effect is much larger. There is a separate topic devoted to this topic here, if anyone wants to learn more about these details:

https://probesoftware.com/smf/index.php?topic=1247.0

So back to Andrew's observations. What Andrew found is that when he was *not* measuring fluorine and was calculating oxygen by stoichiometry in some topaz minerals, the halogen-oxygen correction was being applied correctly as seen here:

That is, when the unanalyzed fluorine is calculated by stoichiometry to stoichiometric oxygen.

However, he found that when he tried to calculate the fluorine by stoichiometry to aluminum (aluminium to some!), the program did not apply the halogen-oxygen correction as expected. This was because it turned out that the element relative to another element code was located *after* the oxygen by stoichiometry code in the matrix iteration. When we moved the element relative to another element code to *before* the oxygen by stoichiometry code, it all worked as seen here:

Any questions?

Probeman · « **Reply #110 on:** August 27, 2021, 09:55:31 AM »

I have a question: is it an "oxygen-halogen" correction, or a "halogen-oxygen" correction?

AndrewLocock · « **Reply #111 on:** August 27, 2021, 10:21:42 AM »

Quote from: Probeman on August 27, 2021, 09:55:31 AM

I have a question: is it an "oxygen-halogen" correction, or a "halogen-oxygen" correction?

"Oxygen equivalent of fluorine" is how it was put by Deer, Howie and Zussman in the Appendix of their book
An Introduction to the Rock-Forming Minerals.

So, more broadly, the oxygen equivalent of the halogen content.

Sorry about the typo in the carbonate example above.
Andrew

John Donovan · « **Reply #112 on:** August 27, 2021, 12:02:57 PM »

Quote from: AndrewLocock on August 27, 2021, 10:21:42 AM

Quote from: Probeman on August 27, 2021, 09:55:31 AM
I have a question: is it an "oxygen-halogen" correction, or a "halogen-oxygen" correction?

"Oxygen equivalent of fluorine" is how it was put by Deer, Howie and Zussman in the Appendix of their book
An Introduction to the Rock-Forming Minerals.

So, more broadly, the oxygen equivalent of the halogen content.

Sorry about the typo in the carbonate example above.
Andrew

OK, then I'm going to use "oxygen-halogen" correction, because I can't usually spell "equivalent" or "equivalence"!

Probeman · « **Reply #113 on:** August 29, 2021, 09:32:15 AM »

I think it's worth demonstrating in some detail exactly how important it is to include these unanalyzed elements in the matrix correction. For example here are the quant results for the above topaz example (data from Locock) with fluorine not included in the matrix iteration:

Un 2 Topaz, Results in Elemental Weight Percents ELEM: Al Si F O TYPE: ANAL ANAL SPEC CALC BGDS: LIN LIN TIME: 20.00 20.00 --- --- BEAM: 15.18 15.18 --- --- ELEM: Al Si F O SUM 6 28.266 15.337 .000 42.617 86.220 7 28.270 15.327 .000 42.608 86.205 8 28.137 15.383 .000 42.555 86.075 9 28.351 15.455 .000 42.827 86.634 10 28.221 15.368 .000 42.611 86.200 AVER: 28.249 15.374 .000 42.644 86.267 SDEV: .078 .051 .000 .106 .213 SERR: .035 .023 .000 .047 %RSD: .28 .33 .00 .25 STDS: 73 73 --- --- STKF: .2305 .1076 --- --- STCT: 448.80 238.86 --- --- UNKF: .2303 .1078 --- --- UNCT: 448.33 239.45 --- --- UNBG: 1.83 1.54 --- --- ZCOR: 1.2268 1.4258 --- --- KRAW: .9990 1.0025 --- --- PKBG: 245.93 156.66 --- ---
And here is with the fluorine included:

Un 2 Topaz, Results in Elemental Weight Percents ELEM: Al Si F O TYPE: ANAL ANAL STOI CALC BGDS: LIN LIN TIME: 20.00 20.00 --- --- BEAM: 15.18 15.18 --- --- ELEM: Al Si F O SUM 6 29.308 15.258 20.647 34.758 99.970 7 29.312 15.247 20.645 34.750 99.954 8 29.176 15.304 20.641 34.696 99.817 9 29.393 15.376 20.675 34.957 100.401 10 29.262 15.288 20.647 34.752 99.948 AVER: 29.290 15.294 20.651 34.783 100.018 SDEV: .080 .051 .014 .101 .223 SERR: .036 .023 .006 .045 %RSD: .27 .33 .07 .29 STDS: 73 73 --- --- STKF: .2305 .1076 --- --- STCT: 448.80 238.86 --- --- UNKF: .2303 .1078 --- --- UNCT: 448.33 239.45 --- --- UNBG: 1.83 1.54 --- --- ZCOR: 1.2720 1.4184 --- --- KRAW: .9990 1.0025 --- --- PKBG: 245.93 156.66 --- ---
Note that the Al concentration changes by around 1 wt% *absolute* or over 3% relative!

And if we don't specify the oxygen-halogen correction to remove the excess stoichiometric oxygen from the matrix iteration, not only is our total way too high but look at the effect on the Al concentration from including that excess oxygen:

Un 2 Topaz, Results in Elemental Weight Percents ELEM: Al Si F O TYPE: ANAL ANAL STOI CALC BGDS: LIN LIN TIME: 20.00 20.00 --- --- BEAM: 15.18 15.18 --- --- ELEM: Al Si F O SUM 6 29.819 15.136 23.211 43.768 111.934 7 29.823 15.125 23.210 43.760 111.918 8 29.685 15.182 23.209 43.702 111.778 9 29.904 15.254 23.233 43.979 112.369 10 29.772 15.166 23.212 43.761 111.911 AVER: 29.801 15.173 23.215 43.794 111.982 SDEV: .080 .051 .010 .106 .225 SERR: .036 .023 .004 .048 %RSD: .27 .34 .04 .24 STDS: 73 73 --- --- STKF: .2305 .1076 --- --- STCT: 448.80 238.86 --- --- UNKF: .2303 .1078 --- --- UNCT: 448.33 239.45 --- --- UNBG: 1.83 1.54 --- --- ZCOR: 1.2942 1.4071 --- --- KRAW: .9990 1.0025 --- --- PKBG: 245.93 156.66 --- ---
Bottom line: whether the element is missing or in excess, it needs to be dealt with the the matrix iteration for accurate results!

Probeman · « **Reply #114 on:** November 05, 2021, 04:52:24 PM »

In this topic we have been emphasizing the importance of including the concentrations of all unanalyzed (specified) elements to obtain an accurate matrix correction, and therefore hopefully, accurate results:

https://www.cambridge.org/core/journals/microscopy-and-microanalysis/article/epma-matrix-correction-all-elements-must-be-present-for-accuracy-four-examples-with-b-c-o-and-f/759C69631A916EA69913539C22989A31

This is because for major elements the most important parameters for analysis accuracy are the accuracy of the matrix correction *and* the accuracy of the standard compositions. For major elements, the accuracy of the background measurement is usually "in the noise", and usually, little affected by spectral interferences.

But what about trace elements? For trace element accuracy, the accuracy of the matrix corrections and standard compositions are not so critical, as it is the accuracy of the background measurements (and spectral interference correction!) that becomes the dominant factor:

https://probesoftware.com/smf/index.php?topic=928.msg8498#msg8498

We can appreciate this point by assuming typical EPMA matrix correction accuracy of say ~2%. If we are measuring a concentration of say, 1000 PPM (0.1 wt%), then 2% of 1000 PPM is 20 PPM (0.002 wt%). A level of accuracy very likely close to the precision of our measurement. Again, usually "in the noise" of our measurement.

We can demonstrate this more clearly in a different manner by making trace element measurements in a material of known composition, the major (and minor) elements being specified to account for the effect of the matrix effects of the unanalyzed elements. Here is the analysis with *no* (unanalyzed) matrix specified:

Un 33 MA-1058 Rxn-1 (trav), Results in Elemental Weight Percents ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC BGDS: MULT MULT MULT MULT MULT TIME: 240.00 240.00 240.00 240.00 240.00 --- --- --- --- --- --- --- --- --- --- BEAM: 80.06 80.06 80.06 80.06 80.06 --- --- --- --- --- --- --- --- --- --- ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O SUM 472 .030 .001 .004 .009 .391 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .436 473 .024 -.001 .002 .003 .323 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .352 474 .013 .002 -.003 .009 .419 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .439 475 .021 .003 -.001 .001 .282 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .306 476 .011 -.002 -.001 .009 .242 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .259 477 .009 .000 .001 .004 .245 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .259 478 .007 .002 .003 .010 .268 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .290 479 .013 .002 .001 .006 .186 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .207 480 .003 -.002 -.002 .002 .129 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .130 481 .010 -.001 .003 .004 .291 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .308 482 .022 .000 .000 .008 .389 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .420 AVER: .015 .000 .001 .006 .288 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .310 SDEV: .008 .002 .002 .003 .089 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .098 SERR: .003 .000 .001 .001 .027 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 %RSD: 55.52 394.62 422.74 53.43 30.94 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 STDS: 257 541 1007 251 22 --- --- --- --- --- --- --- --- --- --- STKF: .4109 .9936 .5384 .4225 .5616 --- --- --- --- --- --- --- --- --- --- STCT: 52.56 382.07 133.42 50.64 82.83 --- --- --- --- --- --- --- --- --- --- UNKF: .0001 .0000 .0000 .0000 .0029 --- --- --- --- --- --- --- --- --- --- UNCT: .02 .00 .00 .01 .42 --- --- --- --- --- --- --- --- --- --- UNBG: .08 .19 .31 .10 .07 --- --- --- --- --- --- --- --- --- --- ZCOR: 1.1199 1.0725 1.0567 1.2265 1.0088 --- --- --- --- --- --- --- --- --- --- KRAW: .0003 .0000 .0000 .0001 .0051 --- --- --- --- --- --- --- --- --- --- PKBG: 1.22 1.01 1.00 1.06 6.68 --- --- --- --- --- --- --- --- --- ---
Note that the total is around 0.3 wt%, mostly from the Ti measurement, therefore the matrix correction has to assume the matrix is almost pure Ti metal. And even if we calculate this as an oxide matrix, nothing changes except the Ti concentration by about 0.017 wt%:

ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC CALC BGDS: MULT MULT MULT MULT MULT TIME: 240.00 240.00 240.00 240.00 240.00 --- --- --- --- --- --- --- --- --- --- BEAM: 80.06 80.06 80.06 80.06 80.06 --- --- --- --- --- --- --- --- --- --- ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O SUM 472 .031 .001 .004 .010 .414 .000 .000 .000 .000 .000 .000 .000 .000 .000 .290 .751 473 .025 -.001 .002 .003 .343 .000 .000 .000 .000 .000 .000 .000 .000 .000 .238 .611 474 .013 .002 -.003 .009 .445 .000 .000 .000 .000 .000 .000 .000 .000 .000 .304 .770 475 .022 .003 -.001 .002 .299 .000 .000 .000 .000 .000 .000 .000 .000 .000 .209 .533 476 .012 -.002 -.001 .009 .257 .000 .000 .000 .000 .000 .000 .000 .000 .000 .176 .450 477 .009 .000 .001 .004 .260 .000 .000 .000 .000 .000 .000 .000 .000 .000 .178 .453 478 .008 .002 .003 .010 .285 .000 .000 .000 .000 .000 .000 .000 .000 .000 .196 .503 479 .013 .002 .001 .006 .197 .000 .000 .000 .000 .000 .000 .000 .000 .000 .138 .357 480 .003 -.002 -.003 .002 .137 .000 .000 .000 .000 .000 .000 .000 .000 .000 .092 .231 481 .010 -.001 .003 .004 .310 .000 .000 .000 .000 .000 .000 .000 .000 .000 .211 .538 482 .023 .000 .001 .008 .413 .000 .000 .000 .000 .000 .000 .000 .000 .000 .286 .731 AVER: .015 .000 .001 .006 .305 .000 .000 .000 .000 .000 .000 .000 .000 .000 .211 .539 SDEV: .009 .002 .002 .003 .094 .000 .000 .000 .000 .000 .000 .000 .000 .000 .066 .169 SERR: .003 .000 .001 .001 .028 .000 .000 .000 .000 .000 .000 .000 .000 .000 .020 %RSD: 55.61 394.67 423.76 51.36 30.90 .00 .00 .00 .00 .00 .00 .00 .00 .00 31.18 STDS: 257 541 1007 251 22 --- --- --- --- --- --- --- --- --- --- STKF: .4109 .9936 .5384 .4225 .5616 --- --- --- --- --- --- --- --- --- --- STCT: 52.56 382.07 133.42 50.64 82.83 --- --- --- --- --- --- --- --- --- --- UNKF: .0001 .0000 .0000 .0001 .0029 --- --- --- --- --- --- --- --- --- --- UNCT: .02 .00 .00 .01 .42 --- --- --- --- --- --- --- --- --- --- UNBG: .08 .19 .31 .10 .07 --- --- --- --- --- --- --- --- --- --- ZCOR: 1.1423 1.1009 1.1251 1.2484 1.0712 --- --- --- --- --- --- --- --- --- --- KRAW: .0003 .0000 .0000 .0001 .0051 --- --- --- --- --- --- --- --- --- --- PKBG: 1.22 1.01 1.00 1.06 6.68 --- --- --- --- --- --- --- --- --- ---
Which we can see is from the change in the matrix correction for Ti Ka by about 6%. The other trace elements still show no change at all. And what happens if we specify the correct matrix correctly as shown here:

Un 33 MA-1058 Rxn-1 (trav), Results in Elemental Weight Percents ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC BGDS: MULT MULT MULT MULT MULT TIME: 240.00 240.00 240.00 240.00 240.00 --- --- --- --- --- --- --- --- --- --- BEAM: 80.06 80.06 80.06 80.06 80.06 --- --- --- --- --- --- --- --- --- --- ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O SUM 472 .040 .002 .005 .011 .462 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.688 473 .032 -.001 .002 .004 .383 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.589 474 .017 .002 -.004 .011 .497 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.692 475 .028 .004 -.002 .003 .334 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.535 476 .015 -.003 -.001 .010 .287 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.476 477 .012 .000 .001 .005 .291 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.478 478 .010 .002 .003 .012 .319 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.513 479 .017 .002 .001 .007 .220 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.415 480 .004 -.002 -.003 .003 .154 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.324 481 .013 -.001 .004 .005 .347 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.536 482 .030 .000 .001 .009 .462 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.670 AVER: .020 .001 .001 .007 .341 23.714 11.392 4.620 4.928 .994 .000 10.125 .108 .089 44.198 100.538 SDEV: .011 .002 .003 .003 .105 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .116 SERR: .003 .001 .001 .001 .032 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 %RSD: 55.77 394.36 423.62 46.10 30.87 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 STDS: 257 541 1007 251 22 --- --- --- --- --- --- --- --- --- --- STKF: .4109 .9936 .5384 .4225 .5616 --- --- --- --- --- --- --- --- --- --- STCT: 52.56 382.07 133.42 50.64 82.83 --- --- --- --- --- --- --- --- --- --- UNKF: .0001 .0000 .0000 .0001 .0029 --- --- --- --- --- --- --- --- --- --- UNCT: .02 .00 .00 .01 .42 --- --- --- --- --- --- --- --- --- --- UNBG: .08 .19 .31 .10 .07 --- --- --- --- --- --- --- --- --- --- ZCOR: 1.4847 1.4029 1.2509 1.3181 1.1972 --- --- --- --- --- --- --- --- --- --- KRAW: .0003 .0000 .0000 .0001 .0051 --- --- --- --- --- --- --- --- --- --- PKBG: 1.22 1.01 1.00 1.07 6.68 --- --- --- --- --- --- --- --- --- ---
Essentially no change in the trace elements, and only a rather small matrix effect on the Ti concentration. Or does it? Let try another matrix, say MgO:

Un 33 MA-1058 Rxn-1 (trav), Results in Elemental Weight Percents ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC BGDS: MULT MULT MULT MULT MULT TIME: 240.00 240.00 240.00 240.00 240.00 --- --- --- --- --- --- --- --- --- --- BEAM: 80.06 80.06 80.06 80.06 80.06 --- --- --- --- --- --- --- --- --- --- ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O SUM 472 .041 .002 .005 .020 .454 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.522 473 .033 -.001 .002 .011 .377 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.422 474 .018 .002 -.004 .019 .489 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.525 475 .029 .004 -.002 .008 .328 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.368 476 .015 -.003 -.001 .019 .282 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.312 477 .012 .000 .001 .012 .286 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.312 478 .010 .002 .003 .021 .313 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.349 479 .017 .002 .001 .015 .216 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.252 480 .004 -.002 -.003 .009 .151 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.160 481 .014 -.001 .004 .012 .341 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.369 482 .031 .000 .001 .018 .454 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.503 AVER: .020 .001 .001 .015 .336 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.372 SDEV: .011 .002 .003 .005 .104 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .115 SERR: .003 .001 .001 .001 .031 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 %RSD: 55.77 394.38 423.62 31.13 30.87 .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 STDS: 257 541 1007 251 22 --- --- --- --- --- --- --- --- --- --- STKF: .4109 .9936 .5384 .4225 .5616 --- --- --- --- --- --- --- --- --- --- STCT: 52.56 382.07 133.42 50.64 82.83 --- --- --- --- --- --- --- --- --- --- UNKF: .0001 .0000 .0000 .0001 .0029 --- --- --- --- --- --- --- --- --- --- UNCT: .02 .00 .00 .01 .42 --- --- --- --- --- --- --- --- --- --- UNBG: .08 .19 .31 .10 .07 --- --- --- --- --- --- --- --- --- --- ZCOR: 1.5270 1.4383 1.2357 1.7923 1.1773 --- --- --- --- --- --- --- --- --- --- KRAW: .0003 .0000 .0000 .0002 .0051 --- --- --- --- --- --- --- --- --- --- PKBG: 1.22 1.01 1.00 1.10 6.68 --- --- --- --- --- --- --- --- --- ---
So we can see that even if we specify the matrix correction completely wrong, for trace elements, at least in this case, there is no significant effect and even for the minor element Ti, we see only a change of 0.025 wt%, or only about 2%.

What's the moral of this story?

1. Matrix corrections and standard composition accuracy is very important for major elements. These items should be your "focus".

2. For trace elements the accuracy of the background correction (and spectral interferences if present) are very important. Matrix corrections and standard composition accuracy, not so much if at all.

3. For minor elements, of course it's a "sliding scale" depending on the peak to background ratio (and the physics details), but if minor element accuracy is important we would want to have accurate background measurements primarily. The accuracy of the standard compositions and matrix correction effects are generally very small for minor elements.

To illustrate this last point here is the sample again calculated using all 10 matrix corrections in Probe for EPMA, where we can see the total variance of the Ti concentrations is quite small:

Summary of All Calculated (averaged) Matrix Corrections: Un 33 MA-1058 Rxn-1 (trav) LINEMU Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV Elemental Weight Percents: ELEM: Zr Nb La Sr Ti Si Ca Al Fe Na K Mg Mn Cr O TOTAL 1 .020 .001 .001 .012 .336 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.370 Armstrong/Love Scott (default) 2 .022 .001 .001 .015 .346 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.385 Conventional Philibert/Duncumb-Reed 3 .021 .001 .001 .013 .335 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.370 Heinrich/Duncumb-Reed 4 .022 .001 .001 .015 .337 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.374 Love-Scott I 5 .021 .001 .001 .013 .336 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.372 Love-Scott II 6 .023 .001 .001 .016 .348 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.388 Packwood Phi(pz) (EPQ-91) 7 .021 .001 .001 .014 .334 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.371 Bastin (original) Phi(pz) 8 .022 .001 .001 .015 .342 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.380 Bastin PROZA Phi(pz) (EPQ-91) 9 .022 .001 .001 .015 .341 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.380 Pouchou and Pichoir-Full (PAP) 10 .022 .001 .001 .014 .342 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.380 Pouchou and Pichoir-Simplified (XPP) AVER: .022 .001 .001 .014 .340 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.377 SDEV: .001 .000 .000 .001 .005 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .007 SERR: .000 .000 .000 .000 .002 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 MIN: .020 .001 .001 .012 .334 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.370 MAX: .023 .001 .001 .016 .348 .000 .000 .000 .000 .000 .000 60.303 .000 .000 39.697 100.388
In fact the Ti variance for all 10 matrix corrections is only 50 PPM

DavidAdams · « **Reply #115 on:** August 22, 2022, 05:51:18 PM »

Quote from: John Donovan on August 19, 2019, 12:07:09 PM

Just FYI, we're just putting the finishing touches on a ferrous/ferric calculation for PFE (and CalcZAF!) that will calculate excess oxygen from ferric iron for minerals using the method of Droop (1987) *and* include it in the matrix correction. This excess oxygen has a surprisingly large effect on the matrix correction physics, even for minerals such as ilmenite/magnetite. I'm just posting this here so we'll have a link for the "interactive help" button in the Calculation Options dialog.

We hope to have a new version of both PFE and CalcZAF uploaded tonight or tomorrow, but first we want to give a big thanks to Andrew Locock, Anette von der Handt, John Fournelle and Emma Bullock, who provided the mineralogical expertise to allow us to implement this.

More details to follow soon but in the meantime the original paper by Droop is attached below

I'm wondering if someone much smarter than me on here can help me think through a problem related to Ferrous/Ferric ratios in glass. I have a series of basaltic glasses that were created by a researcher a long time ago under known and controlled fO2 conditions. A subset of each of these glasses were mounted in epoxy for microprobe analysis and a split of each sample was analysed using wet chemical methods to determine the Ferrous/Ferric content. I can't figure out how I can (if I can) use the relatively new Ferrous/Ferric in the software.

Any help would be greatly appreciated!!!

Probeman · « **Reply #116 on:** August 22, 2022, 06:59:16 PM »

Short answer is you can't for glasses.

The ferric/ferrous excess oxygen calculation is based on charge balance (Droop, 1987) so a formula (number of cations and oxygens) is required for it to work. We even got it to work for most amphibole compositions with a lot of help from Andrew Locock and Aurelien Moy.

But I guess I'm not sure why you want to try this when you already have ferric/ferrous contents from wet chemistry. Just specify the excess oxygen from ferric iron in PFE and it will perform a matrix correction and should give you nicer totals.

AndrewLocock · « **Reply #117 on:** August 23, 2022, 08:17:38 AM »

The following conversions for Fe₂O₃, FeO and excess O may be useful to some.

Conversions between FeO and Fe₂O₃ in wt%:
   Fe₂O₃ = FeO * (159.6882 / [2 * 71.8444]) = FeO * 1.111348
   FeO = Fe₂O₃ * ([2 * 71.8444] / 159.6882) = Fe₂O₃ * 0.8998085

Conversions for Fe³⁺-bearing compounds with "excess oxygen":
   Fe₂O₃ wt% = wt% O "excess oxygen"* (molar mass Fe₂O₃/molar mass O)
   Fe₂O₃wt% = wt% O "excess oxygen" * (159.6882/15.9994)
   Fe₂O₃wt% = wt% O "excess oxygen" * 9.980887

Example: hematite, with 89.981 wt% FeO_total and "excess oxygen" 10.019 wt% O:
   Fe₂O₃ wt% = 10.019 wt% O * 9.980887 = 100.00
   FeO_final = FeO_total – Fe₂O₃ * 0.8998085 = 0.
   Thus, hematite is 100.00 wt% Fe₂O₃

Example: magnetite, with 93.09 wt% FeO_total and "excess oxygen" 6.91 wt% O:
   Fe₂O₃ wt% = 6.91 wt% O * 9.980887 = 68.97
   FeO_final = FeO_total – Fe₂O₃ * 0.8998085 = 93.09 – 62.06 = 31.06
   Thus, magnetite has 68.97 Fe₂O₃ and 31.06 FeO, sum 100.00 wt%

Probeman · « **Reply #118 on:** August 23, 2022, 08:52:05 AM »

Quote from: DavidAdams on August 22, 2022, 05:51:18 PM

Quote from: John Donovan on August 19, 2019, 12:07:09 PM
Just FYI, we're just putting the finishing touches on a ferrous/ferric calculation for PFE (and CalcZAF!) that will calculate excess oxygen from ferric iron for minerals using the method of Droop (1987) *and* include it in the matrix correction. This excess oxygen has a surprisingly large effect on the matrix correction physics, even for minerals such as ilmenite/magnetite. I'm just posting this here so we'll have a link for the "interactive help" button in the Calculation Options dialog.

We hope to have a new version of both PFE and CalcZAF uploaded tonight or tomorrow, but first we want to give a big thanks to Andrew Locock, Anette von der Handt, John Fournelle and Emma Bullock, who provided the mineralogical expertise to allow us to implement this.

More details to follow soon but in the meantime the original paper by Droop is attached below

I'm wondering if someone much smarter than me on here can help me think through a problem related to Ferrous/Ferric ratios in glass. I have a series of basaltic glasses that were created by a researcher a long time ago under known and controlled fO2 conditions. A subset of each of these glasses were mounted in epoxy for microprobe analysis and a split of each sample was analysed using wet chemical methods to determine the Ferrous/Ferric content. I can't figure out how I can (if I can) use the relatively new Ferrous/Ferric in the software.

Any help would be greatly appreciated!!!

Actually I just remembered that there there is a method you might be able to use to determine ferric/ferrous ratios in glasses, but it's non-trivial.

That is the method of water by difference (by analyzing oxygen) first proposed by Barbara Nash at University of Utah. Basically one analyzes for oxygen along with all the cations and then subtracts the oxygen from cations from the analyzed oxygen.

I made a study of this method using the features available in Probe for EPMA (curved backgrounds, Area Peak Factors, empirical mass absorption coefficients, including water in the matrix correction, etc.) on some synthetic glasses from Tony Withers (Universität Bayreuth) and the results are discussed here :

https://probesoftware.com/smf/index.php?topic=922.0

and the details are in the attached pdf at the above link. The point is that in Probe for EPMA one can assign the excess oxygen as water or OH to be included in the matrix correction, or one can simply assume the excess oxygen is due to ferric iron. In all cases some assumptions have to be made.

It was pretty difficult to get enough accuracy with oxygen to obtain an accurate H2O value (but I did analyze them "blind" in the first effort and they came out very close to the FTIR values), and I think it would be even harder to get the excess oxygen from ferric iron, but it might be possible.

DavidAdams · « **Reply #119 on:** August 23, 2022, 02:55:11 PM »

Quote from: AndrewLocock on August 23, 2022, 08:17:38 AM

The following conversions for Fe₂O₃, FeO and excess O may be useful to some.

Conversions between FeO and Fe₂O₃ in wt%:
   Fe₂O₃ = FeO * (159.6882 / [2 * 71.8444]) = FeO * 1.111348
   FeO = Fe₂O₃ * ([2 * 71.8444] / 159.6882) = Fe₂O₃ * 0.8998085

Conversions for Fe³⁺-bearing compounds with "excess oxygen":
   Fe₂O₃ wt% = wt% O "excess oxygen"* (molar mass Fe₂O₃/molar mass O)
   Fe₂O₃wt% = wt% O "excess oxygen" * (159.6882/15.9994)
   Fe₂O₃wt% = wt% O "excess oxygen" * 9.980887

Example: hematite, with 89.981 wt% FeO_total and "excess oxygen" 10.019 wt% O:
   Fe₂O₃ wt% = 10.019 wt% O * 9.980887 = 100.00
   FeO_final = FeO_total – Fe₂O₃ * 0.8998085 = 0.
   Thus, hematite is 100.00 wt% Fe₂O₃

Example: magnetite, with 93.09 wt% FeO_total and "excess oxygen" 6.91 wt% O:
   Fe₂O₃ wt% = 6.91 wt% O * 9.980887 = 68.97
   FeO_final = FeO_total – Fe₂O₃ * 0.8998085 = 93.09 – 62.06 = 31.06
   Thus, magnetite has 68.97 Fe₂O₃ and 31.06 FeO, sum 100.00 wt%

Thanks, Andrew! That's really helpful!

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Author Topic: Specifying Unanalyzed Elements For a Proper Matrix Correction (Read 51453 times)

John Donovan

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

John Donovan

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

John Donovan

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

AndrewLocock

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

John Donovan

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

DavidAdams

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

AndrewLocock

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

Probeman

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction

DavidAdams

Re: Specifying Unanalyzed Elements For a Proper Matrix Correction