General EPMA > EPMA Standard Materials

An Open Letter to the Microanalysis Community

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Probeman:

--- Quote ---“Houston, we have a problem” – Jack Swigert, Apollo 13
--- End quote ---

We also have a problem, though hopefully not one of life or death. However, it is a serious problem and one that requires our collective attention. It is a question of accuracy in the field of microanalysis.

Let's start by asking what might be the largest source of inaccuracy today in microanalysis.

Some of us would say: by *not* using standards. That is, standardless EDS analysis. Unfortunately we seem to have reached an impasse on what can be done about this situation (aside from getting EDS vendors to remove the "Quant" button and getting every SEM lab to obtain proper standards!), so let's put this aside for now, more on this later.

Then what might be the second largest source of inaccuracy in microanalysis today? We would suggest: by using standards!  Now what could we possibly mean by this statement?

Well, 40 years ago there was another problem in microanalysis. Namely that the analytical physical models for matrix corrections at that time were simply not very good. To address this issue, various empirical and semi-empirical methods were developed and tried (e.g., alpha factors, calibration curves, ZAF, etc.). But most of the time, for high accuracy work in these early days, it was usually necessary to utilize "matrix matched” standards. That is, find some "known" material that was similar to our unknowns, in order to minimize the matrix correction extrapolations from the standard to the unknown.  As we all know, if the unknown is the same composition as the standard, the matrix correction is exactly 1.000.

So what did people do? Well, heroes such as Gene Jarosewich and others went into their mineral collections and picked out some large, well crystallized natural specimens and diligently performed wet chemistry and other characterization on the pulverized material. Many of us have made similar efforts in our own laboratories to find such “matrix matched” standards.

Unfortunately these natural materials often had trace and minor element impurities, were inhomogeneous and zoned, containing various inclusions of different minerals and like the restaurant review we've all heard about: the food was terrible, and the portions small. That is, when a request for standard material was made, we would often only receive tiny flyspecks.

Since that time we have been the beneficiaries of many advances in the physical models for matrix corrections (e.g., phi-rho-z models such as PAP, XPP, Brown, Armstrong, improved mass absorption coefficients, improved fluorescence corrections, etc.), so that today we can often obtain accuracy better than 2% relative in most matrices. Sometimes, especially for minor and trace elements, our accuracy is only limited by our measurement precision!  So such “matrix matched” standards are often no longer necessary in many cases. But what is necessary are large quantities of high purity, high accuracy standards!

But here we are today still relying on these sometimes poorly characterized, natural, impure, heterogeneous, inclusion ridden standard materials (and such small portions!), which are now arguably a major source of inaccuracy in our field. See Fournelle, J., & Scott, J. (2017).

Note: due to differences in chemical bonding and coordination, there  can be subtle peak shift and shape effects, and therefore we  may still be required to utilize oxide and silicate standards for analyzing oxide and silicate materials, and sulfide and sulfosalt standards for analyzing sulfide and sulfosalt materials, etc. We can probably live with that!

For possible evidence of these issues see Gale et al., (2013) “The mean composition of ocean ridge basalts” and also Yang et al. (1996) "Experiments and models of anhydrous, basaltic olivine-plagioclase-augite saturated melts from 0.001 to 10 kbar" where they state: "An interlaboratory comparison has been made (Reynolds 1995) including MIT, the Smithsonian Institution in Washington, Lamont Doherty and University of Hawaii. It is the practice in our laboratory to correct microprobe data obtained elsewhere to an MIT reference before making thermobarometric or modeling analyses (see Table 1). Although Grove et al. (1992) neglected to discuss this issue, the Smithsonian data discussed in that paper was corrected before plotting and estimation of crystallization pressure. Failure to do so can result in significant errors, and is most commonly evident as a discrepancy in the pressures estimated from the different equations". Also please see figure 1 below from Penny Wieser for a graphical representation of these various interlaboratory biases.

So what can be done about this situation? Well, notable efforts have been made at NIST to synthesize mineral glass standards, e.g., K-411, K-412 and more recently at the USGS basaltic glasses BCR-2G, BHVO-2G and BIR-1G and these glasses be very useful standards if produced in sufficient (kilogram) quantities so that every microanalysis lab on the planet can obtain them. Compositional characterization of such glasses is however quite non-trivial, but can be done with enough effort. If only such glasses were available in kilogram quantities and freely available. Indeed if they are available in such large quantities, they should be part of every standard collection, but apparently they are not. So what might we do?

We propose that a modest to moderate investment by our international microanalysis community can provide high purity, high accuracy standards for current and future generations of microanalysts.

We propose by utilizing high purity synthetic single crystal materials produced in kilogram quantities every microanalytical laboratory in the world could have access to the same standards. Such end-member single crystals of high purity can be, unlike glass standards which require further compositional characterization, already known in composition!

Note: some questions have been raised as to the degree of, or closeness to, stoichiometry of industrially-produced synthetic materials. Specifically, to what accuracy can the chemical stoichiometry of such single crystals be determined? For example, if a high purity single crystal is homogeneous on the micro-scale, is it also likely to be chemically stoichiometric? This will require further investigation.

E.g., high purity, single crystal Mg2SiO4 should be exactly Mg: 34.550 Si: 19.962 O:  57.143 weight percent (assuming accepted terrestrial isotopic distributions!). And it is grown industrially today as a laser material.

We propose to invest in high purity, stoichiometric (thermodynamically constrained end-member), synthetic standard materials produced in kilogram quantities. Specifically, pure enough single crystals so that homogeneity is not in question (though both purity and homogeneity can be checked), and enough quantity so that *every* microanalytical laboratory in the world has access to the *same* primary standards. In other words, the global standardization of microanalysis, much as was done hundreds of years ago for the metric system, when there were no global standards for commercial or scientific weights and measures. Call it the metrification of microanalysis standards if you will.

We do not propose that these materials be produced in academic/government laboratories; most do not appear set up for kilogram production quantities. However we would very much depend on the expertise of those individuals among our colleagues who are experienced in the growth of such materials to advise us as to what synthetic minerals may be commercially possible. 

Instead, we propose that there are sufficient industrial/commercial resources capable of producing semi-conductor and optical/electronic materials, so that we could contract out the production of such high purity single crystal boules for these standard materials. What standards should we invest in producing?  That is a good question. We think this is for us as a community to decide. Some polling on this question should be organized.

We might guess that the average cost of the synthesis per kilogram of such high purity synthetic standard materials might average around $10K each (pers. comm., Marc Schrier, Calchemist).  Some materials are already available (e.g., SiO2, MgO, Al2O3, MgAl2O4, Mg2SiO4, YAG, YIG, Fe2O3, TiO2, SrTiO3, RbTiOPO4, KTiPO4, MnO, Fe3O4, NiO, ZnO, LaAlO3, MnPSe3, LiTaO3, etc.) and will be a fraction of this cost and can be bought "off the shelf".

Other synthetic minerals may require further research and development, e.g., ZrSiO4 (zircon), ZrO2 (zirconia), HfSiO4 (hafnon), HfO2 (hafnia), ThSiO4 (tetragonal thorite), ThSiO4 (monoclinic huttonite), Fe2SiO4 (fayalite), Mn2SiO4 (tephroite), CaMgSi2O6 (diopside), Al2SiO5 (sillimanite), NaAlSiO4 (nepheline), KAlSi3O8 (sanidine), KAlSi2O6 (leucite), KAlSi3O8 (orthoclase), NaAlSi3O8 (albite), CaAl2Si2O8 (anorthite), Fe3Al2Si3O12 (almandine), PbSiO3 (alamosite), CaAl2O4 (krotite), CaAl4O7 (grossite), CaAl12O19 (hibonite), CaSiO3 (wollastonite), MgSiO3 (enstatite), FeSiO3 (ferrosilite), sulphides (which are seriously lacking since the pioneering days at the USGS-Reston in the 1970s by researchers including Barton, Skinner, Czamanske, Bethke, Toulmin, among others), tellurates, arsenides, niobates, tantalates, etc., may cost 2 or 4 or 10 times this. Let’s do more research on what might be possible at a reasonable cost.

The point being that with further research we believe that other high purity single crystal materials can be identified, developed, characterized and included as useful microanalysis standards in large quantities for use worldwide.

As former directors and presidents of several microanalysis societies, we know the money is available. For example we believe that the Microbeam Analysis Society has accumulated an order of magnitude more money in their funds than would be necessary to fund such a project. By spending around 10 to 30% of just the MAS funds we could secure the global future of high accuracy microanalysis for generations.  If several other national microanalysis societies join this effort, the cost to each society will be an even smaller percentage, and all will benefit.

It should also be noted that such high purity materials could also serve additional purposes such as:

1.   Primary standards to check the compositions of the current standards in every microanalytical lab. If we all are not utilizing the *same* primary standards, what is the point of comparing them?

2.   Primary and secondary standards as a test bed for the community consensus k-ratio database as proposed by Nicholas Ritchie. This means we should strive for at least two standards per element in this effort!

3.   "Blank" materials for trace element analysis and also for mean atomic number (MAN) background standard materials. Six or more “nines” purity is required for use as a trace element blank.

4.   Having these end member high purity synthetics (and maybe some glasses) will really stress our EPMA matrix corrections, dead time calibrations, beam current (Faraday Cup) linearity, not to mention effective takeoff angles and stage tilt on SEM instruments. Such failure mode analysis is essential if we are to make progress in improving these areas of instrumental calibration.

5.   It should also be noted that unlike the “historical accidents” of many of our current standards available today (which are very unlikely to ever be re-created with the same exact compositions), the future production of high purity, single crystal, and thermodynamically constrained standard compositions can always be repeated in the future if necessary. E.g., high purity MgAl2O4 will always be high purity MgAl2O4.

Some possible other items to consider:

6.   The MASFIG committee should establish the minimum qualifications for a candidate standard material to be included in the archive: e.g., characterization by XRD for a crystalline material; independent elemental analysis for a glass; trace measurements by WDS/ICP-MS to establish minimum detectable limit for a specified suite of elements.

7.   It should be noted that in the area of synthetic minerals there are basically two types of candidates: (a) materials already produced at an industrial scale and readily available in kilogram quantities at a fairly reasonable prices (e.g., MgO, Al2O3, MgAl2O4, TiO2, SrTiO3, etc.), and (b) those that are only produced in experimental laboratories in limited (e.g, grams to tens of gram) amounts (e.g., Mg2SiO4, Fe2SiO4, ZrSiO4, Al2SiO5, CaMgSi2O6, etc.).

It must be said that we should probably first concentrate on those materials that are already available in sufficient quantities with reasonable prices to begin with, and then follow up with consultation and investigation of other possible synthetic minerals based on their feasibility of being produced in sufficient quality and quantities.

8.   Establish an on-line database for the information on each standard material, perhaps supported by a non-fungible digital token (NFT) that documents the composition and any other issues, e.g., dose sensitivity, surface layers, etc. This database could include approved additions of information to the analytical record for each material supplied by users. FIGMAS already has a framework for this process.

9.   Establish a site for the repository of the materials, located at a university, museum or national laboratory. 

10.   Establish a strong mechanism for making these standard materials available to customers worldwide, e.g., create working relationships with the vendors who currently provide prepared microanalysis standards. A participating vendor would be given a quantity of the standard material that could be included in that vendor’s prepared microanalysis standards for distribution. A portion of the material supplied to the vendor should also be available for interested customers to purchase (at a nominal cost to cover the vendor’s expenses) individual rough pieces suitable for mounting and polishing by the customer.

11.   These materials may also be useful for other methods of characterization, i.e., Raman spectroscopy, Infrared specular reflectance spectroscopy, Infrared ATR spectroscopy (as powdered material), etc.

Regardless, this is a global analytical issue affecting the microanalysis community. Every microanalysis lab should be able to reference the same primary standard materials if we are to attempt to properly compare our data and results.  If such standard materials are readily available in kilogram quantities, then not only every EPMA lab, but every SEM lab should be able to utilize the same reference materials. Now that would be something worth having for a truly global science of microanalysis.

We are currently in the gathering ideas phase. This effort is clearly one that will foster lots of interest from our community and beyond (as we should hope, with a project such of large scope as this). Please post your comments and ideas to this topic and let’s begin the discussion on how to finally move forward on this critical aspect of our field.
This is an investment not only for ourselves, but for the future of our science, so please join us in these efforts and change the world for future generations (of analysts) to come. They will thank us!

Signed,

Marisa Acosta, University of Lausanne
Dave Adams, Auckland University
Julien Allaz, ETH Zurich
Renat Almeev, Hannover of University
Paul Asimov, California Institute of Technology
Aaron Bell, University of Colorado
Joseph Boro, University of Hawaii
Scott Boroughs, Washington State University
Emma Bullock, Carnegie Institution of Science
Paul Carpenter, Washington University
Henrietta Cathey, Queensland University of Technology
Dave Crabtree, Ontario Geological Survey
Joel Desormeau, University of Nevada, Reno
John Donovan, University of Oregon
Mike Dungan, University of Oregon
Paul Edwards, Strathclyde University
Jon Fellowes, University of Manchester
John Fournelle, University of Wisconsin
Zack Gainsforth, University of California at Berkeley
Raynald Gauvin, McGill University
Karsten Goemann, University of Tasmania
Stacia Gordon, University of Nevada, Reno
Dick Grant, Sandia National Laboratory
Juliane Gross, Rutgers University
Jakub Haifler, Masaryk University
John Hanchar, Memorial University of Newfoundland
Jason Herrin, Nanyang Technological University
Heidi Hoefer, Frankfurt University
Julia Hammer, University of Hawaii
Eric Hellebrand, University of Utrecht
Dominik Hezel, University of Frankfurt
Raymond Jeanloz, University of California, Berkeley
Mike Jercinovic, University of Massachusetts
Brian Joy, Queen’s University
Stuart Kearns, University of Bristol
Adam Kent, Oregon State University
Michael Lance, Oak Ridge Laboratory
Donovan Leonard, Oak Ridge National Laboratory
Yanan Liu, University of Toronto
Xavier Llovet, University of Barcelona
Andrew Locock, University of Alberta
Heather Lowers, United States Geological Survey
Chi Ma, California Institute of Technology
Danny MacDonald, Dalhousie University
Ryan McAleer, USGS, Reston
Mike Matthews, Atomic Weapons Establishment
Francis McCubbin, NASA, Johnson Space Center
Andrew Mott, Texas A&M
Aurelien Moy, University of Wisconsin
Timothy Murphy, Macquarie University
Will Nachlas, University of Wisconsin
Owen Neill, University of Michigan
Angus Netting, University of Adelaide
Dale Newbury, National Institute of Standards and Technology
Phil Orlandini, University of Texas, Austin
Changkun Park, Korea Polar Research Institute
Anne Peslier, NASA, Johnson Space Center
Glenn Poirier, University of Ottawa
Xiaofei Pu, Idaho National Laboratory
Ron Rasch, University of Queensland
Minghua Ren, University of Nevada, Las Vegas
Paul Renne, Berkeley Geochronology Center
Nicholas Ritchie, National Institute of Standards and Technology
Malcolm Roberts, University of Western Australia
George Rossman, California Institute of Technology
Dawn Ruth, USGS Menlo
Gareth Seward, University of California, Santa Barbara
Lang Shi, McGill University
Tom Sisson, USGS Menlo
Giovanni Sosa-Ceballos, , National Autonomous University of Mexico
John Spratt, London Museum of Natural History
Frank Tepley, Oregon State University
Edward Vicenzi, Smithsonian Institution
Anette von der Handt, University of Minnesota
Benjamin Wade, University of Adelaide
Richard Walshaw, University of Leeds
Penny Wieser, Oregon State University
Axel Wittmann, Arizona State University
Karen Wright, Idaho National Laboratory
Panseok Yang, University of Manitoba
Shui-Yuan Yang, China University of Geosciences
Marty Yates, University of Maine
Keewook Yi, Korea Basic Science Institute
Ying Yu, University of Queensland
Zhou Zhang, Zhejiang University
Ryan Ziegler, NASA, Johnson Space Center



Fig 1 - Assessing the effect of interlaboratory biases on Cpx-only and Cpx-Liq thermobarometery using the average reported Cpx and Liq composition from the experiments of Krawcyznski et al. (2012) analyzed on the MIT microprobe.

(a-b) Interlaboratory correction factors for glass from Gale et al., (2013) relative to the Lamont microprobe (plotting at 1, 1).

(c-d) Calculated Cpx-only and Cpx-Liq pressures and temperatures for the average reported composition from Experiment 41c-106, corrected as if these materials were measured in the different laboratories shown in a-b. We assume the Cpx and Glass offsets between different laboratories are identical, as to our knowledge no Cpx round robin has ever taken place.

(e-f) as for c-d, using experiment 41c-108b.

Calculating pressures can vary by ~4 kbar and 50 K just depending on which microprobe analyses were performed on. These systematic offsets between laboratories likely increase the amount of noise in experimental datasets compiled from different laboratories when calibrating different thermobarometric expressions. Similar systematic offsets in pressure and tempreature space can be expected for different groups measuring Cpx and Glass compositions in natural samples to calculate pressures and temperatures. 

For example, for a given natural Cpx composition,  the MIT microprobe might yield ~12.5 kbar, while the Lamont microprobe would yield ~10 kbar (c). These potential offsets largely cannot be corrected retrospectively, as there is insufficient data on the magnitude of offsets between different EPMA laboratories for different geological materials.

See attached pdf (please login to see attachments).

Probeman:
Comments and suggestions for moving forward with this global project are welcome.

Our next efforts will be focused on obtaining some modest amounts (a few grams each?) of 7 or 8 commercially available high purity synthetic materials for mounting to begin their initial characterization.

If anyone can locate or obtain a few grams of these (or other) readily available high purity synthetic materials, please comment below. The idea being a limited set of initial test materials that could be utilized to produce several k-ratio measurements on TAP, PET and LiF Bragg crystals by FIGMAS or other MAS/EMAS/AMAS/JSM/KSEM, etc., members. Also enough extra material to also perform ICP/MS to check for trace elements, XRD for crystallinity, etc...

MgO, Al2O3, MgAl2O4, SiO2, TiO2, SrTiO3, Fe2O3, Fe3O4, YIG, YAG, etc.

Will Nachlas will be coordinating this effort. Please contact Will directly and/or send candidate materials to:

Will Nachlas
Weeks Hall for Geological Sciences
1215 West Dayton St
Madison WI 53706

Will Nachlas <nachlas@wisc.edu>

NicholasRitchie:
Thanks for organizing this John.  It is an important endeavor that will ground the technique for decades to come.

jon_wade:
hi John

I'm broadly sympathetic but I have a few comments.  Firstly, there is a need for microanalytical standards particularly in the LA_ICPMs world and particularly for metals and sulphides. Unfortunately, and for obvious reasons, these are never homogeneous at the scales required - some elements are better than others (like Cu in sulphides) but others are a perennial problem and thats not an easy one to fix.

Secondly, I'm not sure the inclusion of lab comparisons for the CPX barometry is actually that helpful to the cause. You could also include redox sensors in this, but the problems are more protracted as a critic/reviewer may want to look at the accuracy of the experimental data and point an initial finger there, rather than, say,  just the lack of standards.For instance, what is the true error on Pressure and temperature in the experiments how much does grain size in the natural samples/volatile content/prep play a role etc etc.  In reality a single reference secondary standard would provide intra-lab/run consistency and it doesn't really have to be that 'good'. Many groups already offer their published materials as 'standards', such as Mossbauered synthetic spinels or oxygen bearing sulphides.  Yes, they may not always be that great, but they do provide a common reference point and their availability is often key to publication.

finally - why crystals?  why not glasses?  why the extra effort to synthesise a  crystal that will often require a flux? and why the amount?  is there really a need for kg's of sample which will inherently present more issues of homogeneity when a few grams will keep us happy?  they are, after all, micro analytical standards. ;)

Probeman:
Hi Jon,
We appreciate any and all comments. I will try to answer them as best I can, though perhaps I should start by pointing out that participation in this global standards project is completely voluntary.  You can of course continue to utilize your existing standards!   :)


--- Quote from: jon_wade on November 19, 2021, 02:26:41 PM ---I'm broadly sympathetic but I have a few comments.  Firstly, there is a need for microanalytical standards particularly in the LA_ICPMs world and particularly for metals and sulphides. Unfortunately, and for obvious reasons, these are never homogeneous at the scales required - some elements are better than others (like Cu in sulphides) but others are a perennial problem and thats not an easy one to fix.

--- End quote ---

I don't see why you would say that metals and sulfides are obviously never homogeneous. Pure metals which are 99.99% pure would seem to be homogeneous by definition at any scale.  As for sulfides, I have very little experience with natural sulfides, but again, if a synthetic pyrite (not pyrrhotite), is 99.99% pure, how exactly would it be inhomogeneous? 

Incidentally, a long time ago at UC Berkeley I once characterized a half dozen natural well crystallized pyrite cubes (I might still have the mount) and they had identical Fe:S ratios within precision, so that is hopeful at least. But of course any assumed stoichiometries will have to be evaluated on a case by case basis for any proposed synthetic standards.

If you're thinking of trace elements that is something we will investigate of course, but this project is focused on major elements as that is a large source of analytical error today.  But remember, for SEM and even EPMA, anything below say a few PPM is essentially a homogeneous zero.

Just as an aside, in EPMA the best primary standard for a trace element is the pure metal or pure oxide, and the best secondary standard (again for a trace element) is a (roughly) matrix matched zero blank. Then one can determine ones accuracy at zero concentration since it is the background determination that dominates accuracy for trace elements in EPMA. In fact, the use of a zero blank in EPMA is a gift from the science gods as it is one of the few times that one can obtain accuracy equal to ones measurement precision (Donovan et al., 2011).

So it should be noted (as discussed in the open letter) that these proposed high purity synthetic mineral standards can be utilized as not only primary standards, but also as secondary standards. In fact, one additional aspect of this global effort is the compilation of a "k-ratio consensus database" that can be utilized for testing not only our matrix correction physics, but also our instrument calibrations. Hence the necessity of having at least two materials for every element.

And not only standards for blank measurements but also standards for MAN background calibration curves (Donovan et al., 2017). And I'm sure others can think of other uses for high purity stoichiometric synthetic oxides, silicates and sulfides available globally in significant quantities.


--- Quote from: jon_wade on November 19, 2021, 02:26:41 PM ---Secondly, I'm not sure the inclusion of lab comparisons for the CPX barometry is actually that helpful to the cause. You could also include redox sensors in this, but the problems are more protracted as a critic/reviewer may want to look at the accuracy of the experimental data and point an initial finger there, rather than, say,  just the lack of standards.For instance, what is the true error on Pressure and temperature in the experiments how much does grain size in the natural samples/volatile content/prep play a role etc etc.  In reality a single reference secondary standard would provide intra-lab/run consistency and it doesn't really have to be that 'good'. Many groups already offer their published materials as 'standards', such as Mossbauered synthetic spinels or oxygen bearing sulphides.  Yes, they may not always be that great, but they do provide a common reference point and their availability is often key to publication.

--- End quote ---

Well I think you just identified the problem!   :P

Yes, the cpx barometry is just one example shared with us by a geologist (Wieser) who approached us about the issue of inter-laboratory bias, which is apparently of some concern in her field. The question of standard accuracy is of course just one concern of many, but given the well documented problems with many standards utilized by these researchers (e.g., Kakanui augite), it seems reasonable to pursue better and more available standards which can be reproduced relatively easily as needed in the future, rather than the "historical accidents" with which we are limited to today. That is to say, we will never get more of the heterogeneous, inclusion ridden Kakanui augite standard, and for that we should all be grateful I say!   :)

I'll let you geologists discuss the other experimental issues you mention, but this project can help by at least getting us all "on the same page" with regards to our primary standards. As mentioned in the open letter, the situation today in microanalysis is a bit like 400 years ago before the introduction of the global metric system.  But this can be remedied and this project is an effort to begin this process.


--- Quote from: jon_wade on November 19, 2021, 02:26:41 PM ---finally - why crystals?  why not glasses?  why the extra effort to synthesise a  crystal that will often require a flux?

--- End quote ---

We have nothing against glass standards. As discussed in the open letter we do propose utilizing glass standards where they are available in significant quantities and accurately characterized. Ah, but there's the rub. It's not easy to characterize the major elements of a glass composition. Which technique do you trust for this characterization?  As Ben Hansen at Corning Glass said to me recently: who knows what the actual composition of these glasses are? Corning has made a historical decision to rely on XRF calibration curves which I assume relates back to the wet chemistry (gravimetric analysis) of "standard" glasses, but even wet chemistry has its systematic biases.

The other issue with glass standards is that even the NIST K-411 and K-412 glasses are also, when you think about it, just "historical accidents" that will never be exactly reproduced in the future. And there are no more of these materials available today. This is not an ideal situation for long term global standardization.

That said, in my lab when we run say, Mg Ka on synthetic MgO and synthetic Mg2SiO4 against the NIST K-411 and K-412 and BIR-G glasses, we obtain results that agree within precision. Of course this requires that one's dead time constants are precisely calibrated, but it is a sign of hope.


--- Quote from: jon_wade on November 19, 2021, 02:26:41 PM ---and why the amount? is there really a need for kg's of sample which will inherently present more issues of homogeneity when a few grams will keep us happy?  they are, after all, micro analytical standards. ;)

--- End quote ---

Well for one, we are thinking long term: generations of microanalysts. Second we are thinking of making sure that every microanalytical lab in the world has access to these materials. And third we are hoping that each of these labs has sufficient material to withstand repeated re-polishing and re-coating (and sometimes re-mounting) as is often necessary (our lab re-polishes and re-coats our standard mounts every one to two years).

A quick calculation: let's say there are several hundred EPMA instruments in the world, several thousand SEMs and how ever many other instruments that might benefit from global standards, and let's say we distribute 0.25 or 0.5 grams to each lab (as opposed to the usual "fly specks"). Well we can quickly see that quantities of 500 to 1000 grams are pretty reasonable.

I guess the point being, we can do this, we have the resources, and we (more than 90 co-signers) think we should do this. Will you join us?

But again- it's voluntary.

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