NIST Standards!

[John Donovan]

This topic will be focused on the NIST (previously NBS) quantitative standard reference materials (SRM) standards and all associated issues related to obtaining, mounting, characterizing, utilizing, etc., etc., etc.

I will make it "sticky" so it will always be available for newcomers.  Let me know if anyone has other suggestions.

[Probeman]

OK. I'll start this thread off with a comment about the NBS (NIST) mineral glasses which as we all know have had further characterization performed more or less informally by various labs, so here's my lab's contribution:

Here's the output from my standard database for both standards:

St  160 NBS K-412 mineral glass
TakeOff = 40.0  KiloVolt = 15.0  Density =  2.600

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)
Oxide and Elemental Composition

Average Total Oxygen:       43.597     Average Total Weight%:  100.120
Average Calculated Oxygen:  42.797     Average Atomic Number:   12.694
Average Excess Oxygen:        .800     Average Atomic Weight:   21.981

ELEM:     SiO2     FeO     MgO     CaO   Al2O3     MnO       O    Na2O
XRAY:      ka      ka      ka      ka      ka      ka      ka      ka
OXWT:   45.352   9.960  19.331  15.250   9.270    .099    .800    .058
ELWT:   21.199   7.742  11.657  10.899   4.906    .077  43.597    .043
KFAC:    .1621   .0654   .0776   .1008   .0334   .0006   .1738   .0002
ZCOR:   1.3079  1.1840  1.5025  1.0818  1.4676  1.2046  2.5078  1.9910
AT% :   16.571   3.044  10.530   5.970   3.992    .031  59.822    .041
24 O:    6.648   1.221   4.224   2.395   1.601    .012  24.000    .016


St  162 NBS K-411 mineral glass
TakeOff = 40.0  KiloVolt = 15.0  Density =  2.600

SRM 470, NIST
C.M. Taylor (Photometry?) FeO 4.39, Fe2O3 11.23
Total as FeO 14.49, Excess O 1.12
Oxide and Elemental Composition

Average Total Oxygen:       43.558     Average Total Weight%:  100.183
Average Calculated Oxygen:  42.438     Average Atomic Number:   13.227
Average Excess Oxygen:       1.120     Average Atomic Weight:   22.412

ELEM:     SiO2     FeO     MgO     CaO   Al2O3     MnO       O
XRAY:      ka      ka      ka      ka      ka      ka      ka
OXWT:   54.301  14.420  14.671  15.471    .100    .099   1.120
ELWT:   25.382  11.209   8.847  11.057    .053    .077  43.558
KFAC:    .2018   .0950   .0568   .1027   .0004   .0006   .1735
ZCOR:   1.2577  1.1793  1.5585  1.0769  1.4586  1.2001  2.5106
AT% :   20.217   4.490   8.143   6.172    .044    .031  60.903
24 O:    7.967   1.769   3.209   2.432    .017    .012  24.000

Right off you'll note that I've got some FeO/Fe2O3 data so you'll see that there is some "excess oxygen", that is, not all the Fe is as FeO.

Secondly, you will note that there are some trace elements (Na and Mn) that have been documented by several labs.  What does your lab obtain for trace impurities in these NBS (NIST) glasses?

Thirdly, are these glasses still available on the open market?  They are terrific.

[Anette von der Handt]

Hi,

I haven't mounted them yet but I am about to, then I can add to your second point. In regard to your third question, my lab got the K-411 as glass microspheres a few years ago so they should be still available. I found the glass shards online listed at SPI supplies as part of their "30 glasses mounts". I got both as glass shards as a generous gift from John Fournelle. He also recommended them to me as standards for pyroxene analysis.

[John Donovan]

Also check this discussion of mounting the Smithsonian standards which also come in tiny fragments in very small vials:

http://probesoftware.com/smf/index.php?topic=172.0

[Probeman]

In the NIST K-411 and K-412 mineral glasses, one of them (K-411) is not certified for aluminum as it is apparently a zero concentration. I've never looked closely at trying to measure it myself, but I always see a few hundred PPM of Al in K-411 when measuring Al.

Has anyone made a more serious effort to characterize the NIST K-411 mineral glass for Al?
john

[crystalgrower]

So here from the NIST archives is the certificate for the "bulk" form of glasses K-411 and K-412. 

Charles Taylor purchased these and chisel-cut/broke them up for resale. When John Rucklidge purchased these cuts at auction, he had some of them checked by XRF, more to assure that pieces were not mixed, rather than to verify NIST data. Interested parties should contact Astimex Standards directly to see if those WDS were archived. 

The EDS spectra archived at www.2spi.com were collected on the ETEC, low resolution and no Be window for low-energy peaks.  I collected better EDS in 2010 but those files were turned over to Astimex at the time of takeover. Again, asking Astimex  for the 2010 EDS plots directly would be the way to go. I had converted  them all to Excel files at the time. 

FYI the "30 glasses" mount was made only once in duplicate as a custom order and backup.  The second mount was in John's hands in 2010. 
There was no reason to suspect any contamination from polishing of other SPI special order mounts with K-411 and K-412.  The glasses were durable under the older type of petrographic polishing.  By this I mean the predecessor to the heavy-weight fast-acting polishing machines. 

Added later:  I found an old EDS for SiC that definitely had NO Al by XRF-WDS.  The Excel file is attached, and you can see what I guess is causing the false Al in other materials.  Looks like the remedy is a change of background setting.

[Probeman]

In the NIST K-411 and K-412 mineral glasses, one of them (K-411) is not certified for aluminum as it is apparently a zero concentration. I've never looked closely at trying to measure it myself, but I always see a few hundred PPM of Al in K-411 when measuring Al.

Has anyone made a more serious effort to characterize the NIST K-411 mineral glass for Al?

Yes, I can promise that the Al background is curved due to the tail of the Si Ka peak. Here is a figure from my traces in quartz paper that shows this very thing (data from USGS JEOL instrument):



Basically utilizing a linear fit with typical background offsets results in a decrease of about 60-70 PPM for Al ka in a quartz matrix. A link to the full paper is here:

https://epmalab.uoregon.edu/pdfs/3631Donovan.pdf

But this more recent paper is essentially a followup on EPMA trace methods (warning: a lot of statistics!) including using the MAN correction for point analyses and quantitative x-ray maps:

The amazing thing is that the MAN method (when combined with the blank correction for improved accuracy), is that it gives better sensitivity for trace elements (in half the time). 

https://epmalab.uoregon.edu/publ/A%20new%20EPMA%20method%20for%20fast%20trace%20element%20analysis%20in%20simple%20matrices.pdf

And one doesn't have to worry about curved backgrounds *or* off-peak interferences!