How PfEPMA deals with standard compositions

[Malcolm Roberts]

Hi John
Just a quicky to confirm a suspicion of mine. Standard data for a magnetite standard has been incorrectly entered into the standard database causing unknown magnetites to report ca 3.5 wt % higher than these should be. The difference is the excess oxygen. I have dug into a .mdb file and see that PfEPMA does not write the standard compositions to the analysis file, so I guess that it calls these compositions up as required from the standard file. This means that if I correct the error in the standard database, I will have fixed my problem. Am I correct?
Cheers,
Malc.

[John Donovan]

The short answer is "yes".

Just edit the standard.mdb file and the software will utilize the updated standard composition for all quant calculations.

One note however... recently I started saving the standard compositions in each probe MDB database. Why? Just in case someone sends me an MDB file, and the same standards aren't present in my local standard database, the application can now create a "temporary" standard database for looking probe data from other labs. See this post here:

http://probesoftware.com/smf/index.php?topic=42.msg934#msg934

So what that means is that when you edit the standard composition in the standard.mdb file, and re-open your probe database, the program will note that there is a change in the compositions and will ask you which one to update.

In your case you would say"yes" to update the internally stored standard compositions in your probe database.

By the way, after you fix your magnetite composition in your standard.mdb file, it should look something like this:

St  395 Magnetite U.C. #3380
TakeOff = 40.0  KiloVolt = 15.0  Density =  5.200

Port Henry, NY
FeO=30.93% (ISE Carmichael)
Fe2O3=68.85%, FeO=30.92% (as FeO=92.73% + 6.90% O)
(Total FeO=92.73%, by EPMA, JJD)
Oxide and Elemental Composition

Average Total Oxygen:       27.803     Average Total Weight%:  100.229
Average Calculated Oxygen:  20.904     Average Atomic Number:   20.970
Average Excess Oxygen:       6.899     Average Atomic Weight:   32.969

ELEM:      FeO   Al2O3    TiO2     MgO     MnO   Cr2O3     CaO    SiO2       O
XRAY:      ka      ka      ka      ka      ka      ka      ka      ka      ka
OXWT:   92.731    .380    .020    .119    .070    .010    .000    .000   6.899
ELWT:   72.080    .201    .012    .072    .054    .007    .000    .000  27.803
KFAC:    .6779   .0011   .0001   .0003   .0005   .0001   .0000   .0000   .1954
ZCOR:   1.0632  1.7784   .9578  2.2899  1.0822   .8056   .9908  1.4163  1.4231
AT% :   42.454    .245    .008    .097    .032    .004    .000    .000  57.158
24 O:   17.826    .103    .003    .041    .014    .002    .000    .000  24.000


Or like this if one assumes stoichiometry:

St   31 Fe3O4
TakeOff = 40.0  KiloVolt = 15.0  Density =  5.000

Assumed Stoichiometric
Oxide and Elemental Composition

Average Total Oxygen:       27.641     Average Total Weight%:  100.000
Average Calculated Oxygen:  20.731     Average Atomic Number:   21.025
Average Excess Oxygen:       6.910     Average Atomic Weight:   33.077

ELEM:      FeO       O
XRAY:      ka      ka
OXWT:   93.090   6.910
ELWT:   72.359  27.641
KFAC:    .6810   .1946
ZCOR:   1.0626  1.4207
AT% :   42.857  57.143
24 O:   18.000  24.000