And now for something (almost) completely different!
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This is a different situation involving (only) the calculation of stoichiometric (unanalyzed) oxygen in the matrix correction. In this example we have compositions in which one or more halogens replace some of the stoichiometric oxygen sites. This can occur primarily chlor-apatites and fluor-phlogopites, though I'm sure there are cases with other minerals (and glasses) with similar halogen replacement situations (oxygen equivalence).
If you've been following the recent (quite long) discussion involving calculating carbon in carbonates as an unanalyzed element relative to calculated stoichiometric oxygen, you might have seen this code snippet:
' Calculate element relative to stoichiometric oxygen based on previous iteration calculation of oxygen
If zaf.il%(zaf.in0%) = 0 Then ' if calculating oxygen by stoichiometry
For i% = 1 To zaf.in1%
If zaf.il%(i%) = 15 Then
r1!(i%) = (r1!(zaf.in0%) / zaf.atwts!(zaf.in0%)) * sample(1).StoichiometryRatio! * zaf.atwts!(i%)
zaf.ksum! = zaf.ksum! + r1!(i%)
zaf.krat!(i%) = r1!(i%)
End If
Next i%
' Calculate amount of stoichiometric oxygen and add to total
r1!(zaf.in0%) = 0#
For i% = 1 To zaf.in1%
r1!(zaf.in0%) = r1!(zaf.in0%) + r1!(i%) * zaf.p1!(i%)
Next i%
' Calculate equivalent oxygen from halogens and subtract from calculated oxygen if flagged
If UseOxygenFromHalogensCorrectionFlag Then r1!(zaf.in0%) = r1!(zaf.in0%) - ConvertHalogensToOxygen(zaf.in1%, sample(1).Elsyms$(), sample(1).DisableQuantFlag%(), r1!())
' Add to sum
zaf.ksum! = zaf.ksum! + r1!(zaf.in0%)
End If
Note the line of code to calculate the halogen effect on stoichiometric oxygen. This is where a correction for halogens (F, Cl, Br and I) replacing stoichiometric oxygen is made. The idea being that if one calculates stoichiometric oxygen as usual, the total will be too high because the halogen is replacing some of the stoichiometric oxygen. So how much of an effect could this be on the matrix? And why do we care?
Well the effect depends on the composition of the mineral and the particular emitting line in question. And we should care because sometimes the matrix effect of *subtracting* this replaced stoiciometric oxygen is large enough to significantly effect the results.
So here is an example involving chlor-apatite, where the halogen correction has *not* been applied:
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Oxygen Equivalent from Halogens (F/Cl/Br/I), Not Subtracted in the Matrix Correction
Un 5 Cl-apatite as unk, Results in Elemental Weight Percents
ELEM: Si F Cl Mg Ca P Al K O SUM
429 .022 -.545 6.825 .035 38.442 17.751 .006 .000 38.323 100.858
430 .010 -.193 6.868 .028 38.363 17.816 .001 .003 38.354 101.251
431 .015 .173 6.766 .045 38.087 17.885 -.001 -.009 38.346 101.308
432 .026 .123 6.706 .032 38.319 17.901 .004 -.018 38.465 101.557
433 .010 .117 6.890 .022 38.150 17.715 -.003 .011 38.133 101.046
AVER: .017 -.065 6.811 .032 38.272 17.814 .002 -.002 38.324 101.204
SDEV: .007 .305 .075 .009 .149 .081 .004 .011 .120 .266
SERR: .003 .136 .034 .004 .067 .036 .002 .005 .054
%RSD: 41.59 -468.63 1.11 26.47 .39 .46 216.37 -452.12 .31
STDS: 160 284 285 12 285 285 160 374 ---
STKF: .1621 .0256 .0602 .4736 .3596 .1601 .0335 .1132 ---
STCT: 1746.9 73.2 2281.7 18768.4 8605.4 3444.2 5316.8 1646.9 ---
UNKF: .0001 -.0001 .0602 .0002 .3575 .1596 .0000 .0000 ---
UNCT: 1.6 -.4 2281.6 8.3 8554.2 3433.5 1.9 -.4 ---
UNBG: 2.7 4.9 17.5 19.2 33.9 7.1 96.3 10.8 ---
ZCOR: 1.1443 5.1792 1.1305 1.5496 1.0706 1.1163 1.3347 1.0079 ---
KRAW: .0009 -.0049 1.0000 .0004 .9940 .9969 .0004 -.0002 ---
PKBG: 1.60 .93 132.03 1.43 253.74 490.50 1.02 .98 ---
INT%: ---- -102.12 ---- ---- ---- ---- ---- ---- ---As you can see the totals are slightly high because the oxygen has been calculated based on the cations, without consideration of the chlorine oxygen equivalence. In fact for ideal chlor-apatite, the oxygen concentration should be around 36.8 wt%. Now here is the same sample, but with the halogen correction turned on:
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Oxygen Equivalent from Halogens (F/Cl/Br/I), Subtracted in the Matrix Correction
Un 5 Cl-apatite as unk, Results in Elemental Weight Percents
ELEM: Si F Cl Mg Ca P Al K O SUM
429 .022 -.539 6.823 .035 38.429 17.731 .006 .000 36.979 99.486
430 .010 -.187 6.866 .028 38.349 17.794 .001 .003 36.849 99.713
431 .015 .177 6.764 .045 38.071 17.861 -.001 -.009 36.708 99.632
432 .026 .128 6.704 .032 38.304 17.877 .004 -.018 36.861 99.917
433 .010 .122 6.888 .022 38.134 17.691 -.003 .011 36.489 99.365
AVER: .017 -.060 6.809 .032 38.257 17.791 .002 -.002 36.777 99.623
SDEV: .007 .304 .075 .009 .150 .081 .004 .011 .188 .212
SERR: .003 .136 .034 .004 .067 .036 .002 .005 .084
%RSD: 41.59 -509.17 1.11 26.47 .39 .45 216.35 -452.09 .51
STDS: 160 284 285 12 285 285 160 374 ---
STKF: .1621 .0256 .0602 .4736 .3596 .1601 .0335 .1132 ---
STCT: 1746.9 73.2 2281.7 18768.4 8605.4 3444.2 5316.8 1646.9 ---
UNKF: .0001 -.0001 .0602 .0002 .3575 .1596 .0000 .0000 ---
UNCT: 1.6 -.3 2281.6 8.3 8554.2 3433.5 1.9 -.4 ---
UNBG: 2.7 4.9 17.5 19.2 33.9 7.1 96.3 10.8 ---
ZCOR: 1.1424 5.1608 1.1302 1.5466 1.0701 1.1149 1.3325 1.0070 ---
KRAW: .0009 -.0045 1.0000 .0004 .9940 .9969 .0004 -.0002 ---
PKBG: 1.60 .94 132.03 1.43 253.74 490.50 1.02 .98 ---
INT%: ---- -101.99 ---- ---- ---- ---- ---- ---- ---The calculated oxygen is now 36.77 wt%, which is much closer to the ideal 36.8 wt%. The concentrations of the other elements have also decreased slightly, due to the change in the matrix correction from there being less oxygen than before. And the total is somewhat better, but not a big change in any case.
Now let's next consider fluor-phlogopite...