Author Topic: Consensus K-Ratio Measurements  (Read 433 times)

Probeman

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Consensus K-Ratio Measurements
« on: March 16, 2022, 12:46:14 PM »
I'm starting a new topic here on the FIGMAS k-ratio consensus measurements.  This topic is related to the Open Letter to the Microanalysis Community on the effort to develop high purity, high accuracy synthetic silicates and oxides in ~kilogram quantities for global distribution to the microanalysis community as discussed here:

https://probesoftware.com/smf/index.php?topic=1415.0

The initial effort involves small amounts of synthetic materials obtained by John Donovan and Will Nachlas, specifically synthetic MgO, Al2O3 and MgAl2O4. Clearly for high accuracy measurements on such different materials the instrument at least needs to have properly calibrated dead time constants. Especially for modern instruments at moderate beam currents and with large area crystals with higher count rates. And especially Cameca instruments with their typically higher dead time constants!

Have you all actually measured the dead time constants on your instruments or are you simply using the "factory defaults"?  It's important for accuracy and it's not hard! Much helpful information is found here for JEOL instrument dead time calibrations:

https://probesoftware.com/smf/index.php?topic=394.0

Here for Cameca instrument dead time calibrations:

https://probesoftware.com/smf/index.php?topic=33.0

And here is found general information on dead time calibrations (also using the StartWin application for an automated dead time data acquisition):

https://probesoftware.com/smf/index.php?topic=1160.0

Of course other instrument calibrations are also very important.  For example, have you checked the accuracy of your high voltage power supply using the Duane-Hunt limit test?

https://probesoftware.com/smf/index.php?topic=1063.0

Or the tilt on your stage (most important for SEMs)!  Or the effective takeoff angle on your spectrometers?  Or the simultaneous k-ratio test on multiple WDS (or EDS!) spectrometers?

https://probesoftware.com/smf/index.php?topic=369.msg1948#msg1948

These are all important things to check especially as the instrument ages over time. In any event, I wanted to share my own efforts to measure k-ratios on these materials and discuss the effect of the dead time calibration on such k-ratio measurements...

So here are my Mg Ka and Al Ka measurements at 10 nA using element setups that I had (unthinkingly) loaded from 2015 that were using somewhat outdated dead time constants of 3.0 and 2.9 us respectively:

St 3100 Set   3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
 
ELEM:       Mg      Al       O
TYPE:     ANAL    ANAL    SPEC
BGDS:      EXP     EXP
TIME:    40.00   40.00     ---
BEAM:    10.06   10.06     ---

ELEM:       Mg      Al       O   SUM 
   141  17.399  38.789  44.985 101.174
   142  17.300  38.787  44.985 101.073
   143  17.244  38.544  44.985 100.772
   144  17.250  38.722  44.985 100.958
   145  17.329  38.724  44.985 101.038

AVER:   17.305  38.713  44.985 101.003
SDEV:     .064    .100    .000    .150
SERR:     .029    .045    .000
%RSD:      .37     .26     .00

PUBL:   17.084  37.931  44.985 100.000
%VAR:     1.29    2.06     .00
DIFF:     .221    .782    .000
STDS:     3012    3013     ---

STKF:    .4740   .4353     ---
STCT:   582.29  753.61     ---

UNKF:    .1341   .2700     ---
UNCT:   164.74  467.49     ---
UNBG:      .67     .73     ---

ZCOR:   1.2904  1.4336     ---
KRAW:    .2829   .6203     ---
PKBG:   247.22  639.60     ---

As one can see the values compared to ideal stoichiometry aren't too bad, but both are a little high. Of course one could look at different matrix corrections to double check the accuracy, because the matrix correction effects are quite large at 30% and 43% respectively, as seen here:

Summary of All Calculated (averaged) Matrix Corrections:
St 3100 Set   3 MgAl2O4 FIGMAS
LINEMU   Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV

Elemental Weight Percents:
ELEM:       Mg      Al       O   TOTAL
     1  17.305  38.713  44.985 101.003   Armstrong/Love Scott (default)
     2  17.213  39.034  44.985 101.232   Conventional Philibert/Duncumb-Reed
     3  17.276  38.986  44.985 101.247   Heinrich/Duncumb-Reed
     4  17.307  38.887  44.985 101.179   Love-Scott I
     5  17.301  38.704  44.985 100.990   Love-Scott II
     6  17.248  38.500  44.985 100.733   Packwood Phi(pz) (EPQ-91)
     7  17.451  38.831  44.985 101.267   Bastin (original) Phi(pz)
     8  17.333  39.217  44.985 101.535   Bastin PROZA Phi(pz) (EPQ-91)
     9  17.318  39.096  44.985 101.400   Pouchou and Pichoir-Full (PAP)
    10  17.303  38.915  44.985 101.203   Pouchou and Pichoir-Simplified (XPP)

AVER:   17.305  38.888  44.985 101.179
SDEV:     .062    .211    .000    .225
SERR:     .020    .067    .000

MIN:    17.213  38.500  44.985 100.733
MAX:    17.451  39.217  44.985 101.535

So they all look a little high, so what could be the problem?  Well to me this indicates that there may be a problem with a too low dead time correction since the pure oxide (primary) intensities will be lower than expected if the dead time constants are too low (and your spectrometer dead times will only get longer over time as the instrument ages!). And when I looked at the dead time constants in the PFE Elements/Cations window, sure enough they were from a 2015 dead time calibration I had done 7 years ago of 3.0 us and 2.9 us respectively!



So, one could edit the dead time constants for each element in each sample but that would be tedious. If only there was an easier way, and yes there is. Just go to the Analytical | Update Dead Time Constants menu and open the dialog and select all samples (standards and unknowns) and edit the dead time value for that spectrometer (and crystal) as seen here:



By the way, this Update dead Time Constants dialog automatically loads the current dead time constants from the SCALERS.DAT file (it's almost as though it were exactly designed for such a situation!).    ;D

So using the new calibrated dead time constants (from 2019!) of 3.8 us and 3.5 us respectively for Mg and Al, we obtain the following results:

St 3100 Set   3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
 
ELEM:       Mg      Al       O
TYPE:     ANAL    ANAL    SPEC
BGDS:      EXP     EXP
TIME:    40.00   40.00     ---
BEAM:    10.06   10.06     ---

ELEM:       Mg      Al       O   SUM 
   141  17.343  38.710  44.985 101.038
   142  17.244  38.708  44.985 100.938
   143  17.188  38.464  44.985 100.637
   144  17.194  38.643  44.985 100.823
   145  17.273  38.645  44.985 100.903

AVER:   17.248  38.634  44.985 100.868
SDEV:     .064    .100    .000    .150
SERR:     .028    .045    .000
%RSD:      .37     .26     .00

PUBL:   17.084  37.931  44.985 100.000
%VAR:      .96    1.85     .00
DIFF:     .165    .703    .000
STDS:     3012    3013     ---

So now we have relative variances of 0.96% and 1.85% respectively, which really isn't too bad at all for extrapolating from pure MgO and Al2O3 to MgAl2O4. But since that 2019 dead time calibration is now about 3 years old, I going to re-run it as soon as I get a chance. Because if I look at a test run at 6 nA (compared to the previous run at 10 nA) I obtain these results:

St 3100 Set   8 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
 
ELEM:       Mg      Al       O
TYPE:     ANAL    ANAL    SPEC
BGDS:      EXP     EXP
TIME:    40.00   40.00     ---
BEAM:     6.03    6.03     ---

ELEM:       Mg      Al       O   SUM 
   216  17.123  38.535  44.985 100.643
   217  17.230  38.581  44.985 100.797
   218  17.053  38.557  44.985 100.595
   219  17.219  38.757  44.985 100.961
   220  17.199  38.502  44.985 100.686

AVER:   17.165  38.587  44.985 100.737
SDEV:     .075    .100    .000    .146
SERR:     .034    .045    .000
%RSD:      .44     .26     .00

PUBL:   17.084  37.931  44.985 100.000
%VAR:      .47    1.73     .00
DIFF:     .081    .656    .000
STDS:     3012    3013     ---

Now we are even closer with relative variances of 0.47% and 1.73% respectively. So I suspect the dead times have increased slightly since 2019 and so I will run a new dead time calibration and report the new results as soon as Julie let's me have some time on the instrument!  😁
« Last Edit: March 16, 2022, 12:57:36 PM by Probeman »
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NicholasRitchie

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Re: Consensus K-Ratio Measurements
« Reply #1 on: March 17, 2022, 08:31:46 AM »
My experience creating QC systems for multi-laboratory systems is that even "simple samples" identify shortcomings in laboratory procedures.  Part of what excites me about the k-ratio project is that it will allow laboratories to compare their results with other labs in a non-judgemental yet rigorous manner.  EPMA is subtle.  There are many possible ways to introduce small errors that are hard to identify when you don't have a "correct result" to compare against.  Every time I've been involved in one, I've learned something new that improves my procedures.
"Do what you can, with what you have, where you are"
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crystalgrower

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Re: Consensus K-Ratio Measurements
« Reply #2 on: March 19, 2022, 11:57:09 AM »
Having clean stuff isn’t the whole story.  I learned from doing quarterly round robins of 20 labs, to ask a lot of picky questions.  The most frequent issue was  overdue maintenance of the conducting surface.  The numbers told us to overhaul some labs’ equipment and that greatly improved their data. 

(I don’t have access to FIGMAS)

These questions are intended only to collect useful facts:

What about Faraday cups? In fact the exact Faraday Cup used should be a required entry in the k values database.  Is it an aperture in a well or a separate FC?  Is it mounted in the sample holder as opposed to the actual mount? How is it maintained? 

Another required entry should be the COATING ELEMENT, and its COLOR if on steel.  “Carbon coat” ranges in practice from a gold film to a solid shiny black layer.  Other coatings like Os and Au impact data.   

Anyway, there are already about 400 mounts out there that have the following high purity synthetic materials and a FC.  The  mounts are laid out in a distinctive pattern of 53 materials and were sold under several brand names. There should be at least 400 entries for k values in your database right now  using the following:

Periclase MgO,  “quartz” SiO2, “rutile” TiO2,  “calcite” CaCO3, “cuprite” Cu2O, “fluorite” CaF2,  Cr2O3, Y Al garnet Y3Al5O12.  BUT note that in these mounts, “cassiterite” SnO2 is SINTERED.

Of the sulfides in these mounts, “sphalerite” ZnS,  “galena” PbS, “stibnite” Sb2S3 are high purity synthetics. Cinnabar HgS might be really good or might be porous, I guess you would use the S k value from the known synthetics to verify.

Teaching labs should assign the measurement and calculation of k-values to all courses of “instrumental analysis of minerals” to every student.   Getting people into the habit is important.

For a list of suppliers here is https://probesoftware.com/smf/index.php?topic=1223.msg9443#msg9443
« Last Edit: March 19, 2022, 02:08:42 PM by John Donovan »

Probeman

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Re: Consensus K-Ratio Measurements
« Reply #3 on: March 21, 2022, 09:14:13 AM »
I was able to run a new dead time calibration this weekend on the SX100.

Remembering the last dead time calibration from several years ago is shown here:

3.8      3.8      3.5      3.5      3.5     "deadtime in microseconds"

The new dead time calibration from this weekend is shown here:

3.9      4.2      3.7      3.6      2.6     "deadtime in microseconds"

So it appears that 4 of the detectors showed increases in dead time since the last calibration, hence the importance of re-running these dead time calibrations every few years or so. The last detector (spectrometer 5) using a PET crystal had a lot of scatter in the plot (see attached spreadsheet below), so I want to re-run the calibration again, this time maybe using the Ti Ka line on Ti metal (PET and LiF crystals).

Eventually, I will edit the SCALERS.DAT file on the probe computer, but in the mean time let's review the last quantitative results from the MgO, Al2O3 and MgAl2O4 FIGMAS mount using a beam current of 10 nA and the dead time constants from 2015:

St 3100 Set   3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
 
ELEM:       Mg      Al       O
TYPE:     ANAL    ANAL    SPEC
BGDS:      EXP     EXP
TIME:    40.00   40.00     ---
BEAM:    10.06   10.06     ---

ELEM:       Mg      Al       O   SUM
   141  17.343  38.710  44.985 101.038
   142  17.244  38.708  44.985 100.938
   143  17.188  38.464  44.985 100.637
   144  17.194  38.643  44.985 100.823
   145  17.273  38.645  44.985 100.903

AVER:   17.248  38.634  44.985 100.868
SDEV:     .064    .100    .000    .150
SERR:     .028    .045    .000
%RSD:      .37     .26     .00

PUBL:   17.084  37.931  44.985 100.000
%VAR:      .96    1.85     .00
DIFF:     .165    .703    .000
STDS:     3012    3013     ---

Where we see relative variances for Mg and Al of 0.96% and 1.85%. After using the handy dandy Analytical | Update Dead Time Constants menu dialog for the new dead time constants, from this weekend, for spectrometers 1 and 4, we now obtain:

St 3100 Set   3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
 
ELEM:       Mg      Al       O
TYPE:     ANAL    ANAL    SPEC
BGDS:      EXP     EXP
TIME:    40.00   40.00     ---
BEAM:    10.06   10.06     ---

ELEM:       Mg      Al       O   SUM 
   141  17.336  38.698  44.985 101.020
   142  17.238  38.696  44.985 100.919
   143  17.181  38.452  44.985 100.619
   144  17.188  38.632  44.985 100.804
   145  17.266  38.633  44.985 100.885

AVER:   17.242  38.622  44.985 100.849
SDEV:     .064    .100    .000    .150
SERR:     .028    .045    .000
%RSD:      .37     .26     .00

PUBL:   17.084  37.931  44.985 100.000
%VAR:      .92    1.82     .00
DIFF:     .158    .691    .000
STDS:     3012    3013     ---

So now we have slightly smaller variances of 0.92% and 1.82%, so not a significant difference, but again an accuracy improvement in the right direction.
« Last Edit: March 21, 2022, 09:16:02 AM by Probeman »
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crystalgrower

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Re: Consensus K-Ratio Measurements
« Reply #4 on: May 11, 2022, 08:15:10 AM »
Why isn't any other lab posting theirs?

It may be useful to separate the two goals articulated in the Open Letter.

The collection of a k-values database absolutely does not require the creation and distribution of a new materials collection.  Mount makers have been selling high-purity synthetic oxides for over 50 years  and there should be something like 2,000 mounts worldwide that have adequate documentation of purity and supplier. Use google to get links to at least 10 different former and present manufacturers (not resellers).

The highest uptake of a database would be for NIST or a parallel body to set this up formally as a NIST effort.
An online table with space to make entries about k-value with material, known provenance and purity, instrumentation, Faraday cup used for data collection, software used, etc could be created.  The manager would have to back up such a data-entry table daily to prevent deletions.  Other ideas about security don’t  need to be public.

The data should be collated into a second anonymous  table for public distribution.  Absence of identification is necessary to secure widespread participation.

Chemistry and physics societies could help greatly to engage universal participation in a k-values project  because this science is part of their mission. The increase of international linking of physics societies to the American Institute of Physics  has promoted  open access to even archival material that is searchable in English as well as the original language.
In contrast, participation in FIGMAS requires paid membership to a limited list of microscopy societies PLUS a membership fee to FIGMAS itself. 

And to those who purchase materials for any distribution, please consider a more efficient process of material verification.  For example:

Polarized light microscopy of batches of pieces immersed in a petri dish of water or isopropanol is essential. 

Powder XRD on one subsample passing PLM is more than enough to confirm the phase. 

SEM examination of one polished/mounted  subsample will confirm whether the material is sintered—in case the PLM fails to catch this.

If the prior steps show  evidence that the manufacturer’s certificate is unreliable then NO further effort should be made. 

Batch XRF-WDX on 50-100 grams of 2mm loose pieces is the best way to determine  trace contaminants.   NO you are not trying to assay the major component, just the level of contamination.

Wet chemistry that is performed under conditions that guarantee the absence of contamination during dissolution is so expensive that it is really  not a priority.  Some good EPMA materials simply do not dissolve easily.

LA-ICP-MS is absolutely not a batch technique. Neither is EPMA.

Probeman

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Re: Consensus K-Ratio Measurements
« Reply #5 on: May 11, 2022, 09:12:46 AM »
No one is posting consensus k-ratios here. I'm just sharing my surprise and pleasure with some quant results.  Related to this I'm also collecting k-ratios at different beam currents for the possible purpose of a better dead time calibration procedure.  More on this soon.

In the meantime the FIGMAS group is working with the initial participants and is collating results returned to them for the specific materials currently being distributed.  More materials are "in the pipeline".   I'm as impatient as you are...   :D

Indeed there are many synthetic oxides "out there", but we want to utilize materials that we know are currently available in bulk quantities, so we are starting afresh working with various suppliers.

The characterization of high purity synthetic materials is indeed a separate process from the k-ratio data collection. Your suggestions for bulk purity characterization are helpful. Thanks.
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John Donovan

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Re: Consensus K-Ratio Measurements
« Reply #6 on: May 15, 2022, 05:57:48 PM »
We added a new feature to Probe for EPMA to assist in the accurate acquisition of consensus k-ratios.

If you're like some people and utilized element setups from the SETUP.MDB element database or loaded a sample setup from a previous Probe for EPMA run, you probably loaded the element setups, then peaked the spectrometers, checked the PHA settings and maybe even re-ran a wavescan sample to check on your off-peaks, but that might not be enough.

Recently Probeman contacted us to let us know that although he did all of the above, when loading the element setups from previous runs, he neglected to note that the dead time constants for his WDS spectrometers had since been re-calibrated. Therefore that the stored elemental setups still referenced the old dead time constants, from prior to the dead time re-calibration.  And they should of course since they are a record of that calibration!  ::)

But to prevent this from happening again, in the latest version of Probe for EPMA, if one has updated the dead time constants in the SCALERS.DAT file since those element setups were saved, Probe for EPMA will now check for this and provide the following user dialog, if it finds that the dead time constants have been updated since then:



Therefore this new PFE update will allow one to utilize older element setups but with the new dead time calibrations from the SCALERS.DAT file.

Of course one can always manually update these dead time constants "after the fact" using the Analytical | Update Dead Time Constants menu dialog as described here:

https://probesoftware.com/smf/index.php?topic=1442.msg10641#msg10641
« Last Edit: May 15, 2022, 10:15:56 PM by John Donovan »
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