An Open Letter to the Microanalysis Community

[Probeman]

“Houston, we have a problem” – Jack Swigert, Apollo 13

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>

[Nicholas Ritchie]

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!   

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.

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.

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.

Well I think you just identified the problem!   

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.

finally - why crystals?  why not glasses?  why the extra effort to synthesise a  crystal that will often require a flux?

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.

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.

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.

[sem-geologist]

High purity and high quality synthetic substances... Where should I sign?   

I want to point also to few addition small issues and features, which planning of these synthetics IMHO should take into consideration.

1. under-beam stability. Synthetic, but beam-unstable substance will fail miserably as inter-institutional standardization will highly depend from analyst skills/experience on instrument to mitigate those effects. In such case not so pure - but stable minerals would give better inter-lab standardized results. Thus said, I am sceptical about proposed ThSiO4 which is beam unstable, why not simple ThO2? Same for U - UO2 (using depleted U) is what I really recommend. However, for U and Th synthetic minerals there could be problem with distribution in some countries, which have stellar-magnitude-paranoia on that point. Labs  in these countries are doomed to be able to use only low concentration poor-quality glass'es (Last time hear story from some Asian country, It needs to be confirmed). Also we need something stable for Na - which can be challenging to find. So even if We would use such unstable minerals as secondary standards - the goal of getting universal k-ratios would stand on skill and experience of analyst. Another concern for obtaining universal k-ratios is that some biases can be introduced by poor-designed dead-time correction (especially on WDS systems of Jeol and Cameca, where is no pile-up correction).

2. For EDS (especially in case of DTSA-II and NeXL library) it is good to have standard reference material where given peaks are away from other element peaks, so that they could be used as reference (shape) peaks. Thus said, proposed LaAlO3 is poor standard in that case as resolving M lines of La would be possible only by de-convolution, but physical models ...grrr... ignores existence of LREE Ma lines - which produces rubbish deconvolution. Why not use widely available LaB6? The same for other LREE and MREE elements: CeB6, PrB6, NdB6, SmB6, EuB6, GdB6?  These are more and more produced are very beam stable (primary use as cathode, much higher temperatures than what we can get with beam-iradiation). I think from Tb toward Lu it could be oxides or fluorides, but substances should not contain Al or Si as that would complicate M line resolution (deconvolution). Of course these could be said to be the concern of EDS (DTSA-II, NeXL and not PfS concern) and thus is out of scope of this initiative, as PfS can do interference correction on standard (I guess) and WDS in many cases has enough resolution to not get these interferences. However, ignoring these points makes this initiative less universal and more PfS oriented then.

3. Sulfides. Again it is not enough to have only pure standards produced, as most of them degrade. To do the right analyses of sulphides is really a huge challenge - Samples (and reference samples for standardization) needs to be re-polished before to get away the oxidated layer. The handling of sample during and between re-polishing-drying-re-coating-placing-into-chamber will have much more bigger impact than homogeneity of the sulphide reference (I don't recall I ever saw non-homogeneous sulfide standard). Pyrite as a standard is really very very bad chose.

4. I also can't understand why we need 1 kg lump of standard. If there is known process how to do very clean crystallization, why can't it be then multitude of small pieces - which is easier to produce on demand and less waste when dividing. Lets say we get 1 Kg of X mineral. How it will be divided into thousand of pieces? Sawing it (mechanically or with laser) will produce lots of waste. Crushing also would produce some powder - it is not possible to divide without any waste. Producing thousand of small pieces is more efficient, as then there is no need to divide this huge lumps. This point can be completely irrelevant for say synth-wollastonite, but Would generate additional high cost for lets say REE minerals.

So I am all in for this initiative, but not for global reasons (k-ratio DB), which this would be only a small step-toward (but not sufficient on its own), but for more excellent standards available for me, and Now. We are already late, we need these standards yesterday, not for future generations (technology improves, possibly future generations will have much easier means to analyse and synthesize the minerals, it is very probably that no-one would even appreciate this initiative as it could get irrelevant in the future). Every day we use those not-perfect natural minerals as references, and publish such data – we weave this imperfection into whole global scientific fabric. It is very often that even if we update the data in further publications, no-one cares about it at all, the initial values already are circulated, compared against, migrated to some process modelling (and progress these imperfections further and further, which IMHO is near impossible to stop by any erratas or addendum). From other side we need to do analysis to keep the labs running, we can't just stop everything and say we are waiting for a full set of excellent reference materials covering (near-)whole element table. 

P.S. We prefare synth as reference, if available for given element and ox state. But we never use then blindly, all our reference materials are internally checked for homogeneity and trace amount of contaminants (mostly by High Current, full extent, extended-time wavescans). In our lab, only about ~60-70% of bought reference substances can be said that are in agreement to the declared purity and composition. The resolution of issues with standards is actually what discriminate good lab from inferior lab, which blindly believes in ISO's and certificates. And that brings me to this economical, management, political problems:

5. Price and ISO certificate. The biggest, and largest impact on global correctness of analysis could be achieved for new labs, which are going to search for obtaining standards. Unfortunately, most of labs will look to price and available certificates (so that lab could be accredited). Lots of already established SEM labs are not going to be interested, because why? They already have ISO certificated standards, why they should invest in another standards? It is going to be pain to make majority of SEM labs to make any investment in this. (Just think how in the first place it is hard to turn the industry/ EDS vendors away from standartless-EDS analyses). How this initiative is going to deal with concurrency of well established biggest suppliers (SPI, MAC...)? - This leads to very important issue: Do we really need to over-invest in kg scale standards? That implies it should be cheaper than what SPI and MAC and etc... provides, It should also have ISO certificates (which again are additional cost). And even then, Simple-manged SEM lab is more keen to buy the set of standards (like 50 different pieces factory-mounted in copper 1-inch round mount), than to buy separate bulk standards and do its own mounts. Us, EPMA probers are minority in the industry and scientific institutions, I have really huge doubt if this kg scale is not huge exaggeration which will fire-back on the price for us, who are the most interested in this initiative (and i.e. I am not interested in very lax ISO certificates, neither I would be interested for additional charged for that orders-of-magnitude less strict from our internal protocols rubbish (ISO compliance)). Would it be possible to cooperate with SPI, MAC and other big vendors so that they would sell this, and throw out half of the rubbish they sell now?

[jon_wade]

my comments re: sulfides and metal was really focused on trace elements in standards.  These are rarely homogenous, but there is a desperate need for such in the LA-ICPMS community (et al) where matrix matching is a bigger issue.  Of course, 'pure' standards' should be pure - stands to reason, which is why I favour a good metals block over some of our 'pure' synthetic stuff (MgO is a good example of a commercially available single crystal that we've found is often not as 'pure' as all that).  Sulfides are a particular problem as noted above, and I would be pleasantly surprised if you can make a significant amount that are both 'pure' and stoichiometrically identical. 

I  think a lot could be done to educate current probe users about the role of standard (ahem, SJIO), background selection and instrument operating conditions which would go someway to mitigating a lot of issues (honestly, theres still papers published where dead times in olivine are hit. worrying about your standard is a little moot when that happens!).  I honestly feel the cost/benefits of this mammoth effort isn't there without embracing other microanalytical communities. Perhaps it would be worth doing a thorough market survey of demand (and not just 'I'd like some!' but 'how much would you like some?').  It may also be instructive as my gut feeling is the EPMA community at a research funding level is not in such rude health.

[wonachlas]

The Focused Interest Group on MicroAnalytical Standards (FIGMAS), a FIG of the Microscopy Society of America (MSA) and co-sponsored by the Microanalysis Society (MAS), is organizing a series of round robin exercises to begin investigating synthetic standard materials for developing a universal standards mount and accompanying database of community k-ratios. Details of the round robin and a survey to express interest are included in the link below. All labs who meet the stated criteria are welcome to participate.

https://docs.google.com/forms/d/e/1FAIpQLSd8nttQYcex9UmnHJyD3iHE-vpL7gG5XVpNumX8-fqrWrgb9A/viewform

[Probeman]

High purity and high quality synthetic substances... Where should I sign?   

I want to point also to few addition small issues and features, which planning of these synthetics IMHO should take into consideration.

Great comments. I will respond as best I can below.

1. under-beam stability. Synthetic, but beam-unstable substance will fail miserably as inter-institutional standardization will highly depend from analyst skills/experience on instrument to mitigate those effects. In such case not so pure - but stable minerals would give better inter-lab standardized results. Thus said, I am sceptical about proposed ThSiO4 which is beam unstable, why not simple ThO2? Same for U - UO2 (using depleted U) is what I really recommend. However, for U and Th synthetic minerals there could be problem with distribution in some countries, which have stellar-magnitude-paranoia on that point. Labs  in these countries are doomed to be able to use only low concentration poor-quality glass'es (Last time hear story from some Asian country, It needs to be confirmed). Also we need something stable for Na - which can be challenging to find. So even if We would use such unstable minerals as secondary standards - the goal of getting universal k-ratios would stand on skill and experience of analyst. Another concern for obtaining universal k-ratios is that some biases can be introduced by poor-designed dead-time correction (especially on WDS systems of Jeol and Cameca, where is no pile-up correction).

Characterization of beam stability is of course one of our concerns. We propose to carefully characterize all potential candidates for purity, stoichiometry, homogeneity and beam stability as described in the open letter. 

Though I am surprised by your mention of ThSiO4 beam stability as I have both synthetic huttonite and thorite from John Hanchar and both seemed to be quite beam stable, though it has been years since I looked at them. However almost every material is beam unstable at some level given sufficient beam focus and beam currents. I will have to re-examine these materials. That said, ThO2 and UO2 would be excellent standards, though we would prefer at least two materials for each element in order to make k-ratio measurements.

However, I am heartened by my experience of beam stability in many other crystal synthetics, for example RbTiOPO4 as a Rb standard which is wonderfully beam stable. Interestingly there is also a widely available KTiOPO4 synthetic which would be worth testing for K stability. Would anyone be willing to provide us with a few grams for testing?

In the past we have also discussed synthesis of a Cs zircono phosphate material... certainly something like this would be better than the usual "fly specks" of pollucite that are sometimes circulated:

https://probesoftware.com/smf/index.php?topic=560.msg6674#msg6674

As for "universal" or as I call them "consensus" k-ratios, you are correct, this indeed will be a significant amount of work. However, eventually once these materials are properly characterized they could also be used to test instrumental performance, e.g., dead time calibrations, effective take off angles, beam current linearity, etc. not to mention matrix correction models, etc. as described in the open letter.

It must also be pointed out that such "consensus" k-ratio measurements will not be arrived at naively, but rather will be evaluated carefully to obtain to most accurate values possible. In other words if ones WDS detectors are not already carefully calibrated for dead time, ones reported k-ratios will not be helpful. The skill and dedication of the operator will indeed be a critical factor in such measurements.  I can think of a handful of such people that I would immediately trust...

2. For EDS (especially in case of DTSA-II and NeXL library) it is good to have standard reference material where given peaks are away from other element peaks, so that they could be used as reference (shape) peaks. Thus said, proposed LaAlO3 is poor standard in that case as resolving M lines of La would be possible only by de-convolution, but physical models ...grrr... ignores existence of LREE Ma lines - which produces rubbish deconvolution. Why not use widely available LaB6? The same for other LREE and MREE elements: CeB6, PrB6, NdB6, SmB6, EuB6, GdB6?  These are more and more produced are very beam stable (primary use as cathode, much higher temperatures than what we can get with beam-iradiation). I think from Tb toward Lu it could be oxides or fluorides, but substances should not contain Al or Si as that would complicate M line resolution (deconvolution). Of course these could be said to be the concern of EDS (DTSA-II, NeXL and not PfS concern) and thus is out of scope of this initiative, as PfS can do interference correction on standard (I guess) and WDS in many cases has enough resolution to not get these interferences. However, ignoring these points makes this initiative less universal and more PfS oriented then.

Good and widely available standards for quant EDS are certainly important as mentioned in the open letter. Your suggestion of REE borides and fluorides is a good idea. Would you be willing to investigate the commercial availability and pricing of such high purity REE borides and fluorides for us? We would be very interested. I know that high purity BaF2 and MgF2 are easily available. But with LaB6 is it high purity?  Please find out for us.

I should emphasize, this global effort has nothing to do with any particular software or vendor. Yes, EDS will struggle with some WDS standards for creating valid profile spectra, but certainly simple synthetics will usually be a better bet than some natural material loaded with various minor elements. LA-ICPMS will also require trace element homogeneity, and that will be another aspect to consider.  But we need to start somewhere and not get overwhelmed by satisfying every possible criteria immediately.

Since EPMA geologists are generally most concerned with major and minor element accuracy, we say let's start with suitable primary and secondary standards for EPMA geology and see what we can obtain.  This of course, is not to exclude any SEM geologists!   

3. Sulfides. Again it is not enough to have only pure standards produced, as most of them degrade. To do the right analyses of sulphides is really a huge challenge - Samples (and reference samples for standardization) needs to be re-polished before to get away the oxidated layer. The handling of sample during and between re-polishing-drying-re-coating-placing-into-chamber will have much more bigger impact than homogeneity of the sulphide reference (I don't recall I ever saw non-homogeneous sulfide standard). Pyrite as a standard is really very very bad chose.

I'm sure sulfides will be a challenge which is why we have started looking at synthetic oxides and silicates. Sulfides were mentioned in the open letter because some co-signers felt we shouldn't exclude the ore people. If these types of standards are important to your work, perhaps you could help us research commercially available synthetic materials?  Please ask about purity, stoichiometry, pricing and availability. First in amounts of a few grams for initial testing and characterization, but eventually in larger quantities for global distribution.

Curious: why would high purity synthetic pyrite be such a bad standard material? Seems quite stable when I've used it at 30 nA and 20 keV.  Then again I usually run my standards slightly defocused or turn on the TDI correction.

4. I also can't understand why we need 1 kg lump of standard. If there is known process how to do very clean crystallization, why can't it be then multitude of small pieces - which is easier to produce on demand and less waste when dividing. Lets say we get 1 Kg of X mineral. How it will be divided into thousand of pieces? Sawing it (mechanically or with laser) will produce lots of waste. Crushing also would produce some powder - it is not possible to divide without any waste. Producing thousand of small pieces is more efficient, as then there is no need to divide this huge lumps. This point can be completely irrelevant for say synth-wollastonite, but Would generate additional high cost for lets say REE minerals.

The eventual need for 500 to 1000 gram quantities is explained in my response to Jon Wade above. As for waste, there will always be some produced, but I'm sure we can minimize that problem. We are already discussing with some vendors that single crystal boules are not necessary, as long as the pieces are at least millimeters in size and crystalline.

It all depends on how the crystal material is produced. If produced as a single boules it will have to be sawn or crushed. This may be unavoidable depending on how it is supplied to us.

So I am all in for this initiative, but not for global reasons (k-ratio DB), which this would be only a small step-toward (but not sufficient on its own), but for more excellent standards available for me, and Now. We are already late, we need these standards yesterday, not for future generations (technology improves, possibly future generations will have much easier means to analyse and synthesize the minerals, it is very probably that no-one would even appreciate this initiative as it could get irrelevant in the future). Every day we use those not-perfect natural minerals as references, and publish such data – we weave this imperfection into whole global scientific fabric. It is very often that even if we update the data in further publications, no-one cares about it at all, the initial values already are circulated, compared against, migrated to some process modelling (and progress these imperfections further and further, which IMHO is near impossible to stop by any erratas or addendum). From other side we need to do analysis to keep the labs running, we can't just stop everything and say we are waiting for a full set of excellent reference materials covering (near-)whole element table. 

We all want excellent standards now (or even yesterday would be nice), but most of us live in the real world and know that a scientific project as presented in the open letter requires time, money, cooperation and a lot of effort. I'm sure you agree.

And no one is saying we have to stop all current lab work immediately until this project is complete. Where did you see that mentioned in the open letter?   

Everyone will have their own reasons for joining this project, we hope you will find sufficient reasons of your own to help us in this global effort. It might be one of the most enduring contributions we can make to our field.

P.S. We prefare synth as reference, if available for given element and ox state. But we never use then blindly, all our reference materials are internally checked for homogeneity and trace amount of contaminants (mostly by High Current, full extent, extended-time wavescans). In our lab, only about ~60-70% of bought reference substances can be said that are in agreement to the declared purity and composition. The resolution of issues with standards is actually what discriminate good lab from inferior lab, which blindly believes in ISO's and certificates. And that brings me to this economical, management, political problems:

Good for you. I wish all labs worked so diligently on their standard materials. 

I am reminded of occasions when I have been contacted by some EPMAers attempting to utilize the MAN background correction (Donovan et al, 2017), and been told that they had no idea that their standards were so contaminated with minor and trace elements...   

5. Price and ISO certificate. The biggest, and largest impact on global correctness of analysis could be achieved for new labs, which are going to search for obtaining standards. Unfortunately, most of labs will look to price and available certificates (so that lab could be accredited). Lots of already established SEM labs are not going to be interested, because why? They already have ISO certificated standards, why they should invest in another standards? It is going to be pain to make majority of SEM labs to make any investment in this. (Just think how in the first place it is hard to turn the industry/ EDS vendors away from standartless-EDS analyses). How this initiative is going to deal with concurrency of well established biggest suppliers (SPI, MAC...)? - This leads to very important issue: Do we really need to over-invest in kg scale standards? That implies it should be cheaper than what SPI and MAC and etc... provides, It should also have ISO certificates (which again are additional cost). And even then, Simple-manged SEM lab is more keen to buy the set of standards (like 50 different pieces factory-mounted in copper 1-inch round mount), than to buy separate bulk standards and do its own mounts. Us, EPMA probers are minority in the industry and scientific institutions, I have really huge doubt if this kg scale is not huge exaggeration which will fire-back on the price for us, who are the most interested in this initiative (and i.e. I am not interested in very lax ISO certificates, neither I would be interested for additional charged for that orders-of-magnitude less strict from our internal protocols rubbish (ISO compliance)). Would it be possible to cooperate with SPI, MAC and other big vendors so that they would sell this, and throw out half of the rubbish they sell now?

This issue of cost and working with commercial microanalysis providers has been discussed on a number of Zoom calls with many of the co-signers, and we have made a few decisions regarding your points above:

1. These samples will be developed by volunteers in the microanalysis community and any commercially sourced materials will be purchased through grants and matching funds. As mentioned in the open letter several microanalysis societies have more than sufficient funding to get this project well on its way. Several of our members are already beginning the process of grant writing to further extend our purchasing power.

That said. there are possibilities of obtaining synthetic crystal material from state sponsored crystal growing projects which, if located, might be freely available. In addition, some of us have been able to obtain hundreds of grams of various synthetic materials from commercial crystal producers for *free* by asking nicely if they have any scraps or "cutoffs" from their boules!  If you don't ask, you already know the answer!   

So the plan is that these materials will be provided for free to qualifying laboratories. A good first step in that qualification process is to join the FIGMAS:

https://figmas.org/about.php

2. In order to provide a long term and stable repository for these synthetic materials, we have been informed that the Smithsonian Institution would be pleased to provide this service for our global standards project, but they cannot have any association with commercial providers that would be making a profit from the sale of these materials.

3. The question of ISO certification is outside my area of expertise, but maybe some else can chime in on this?

[Nicholas Ritchie]

2. In order to provide a long term and stable repository for these synthetic materials, we have been informed that the Smithsonian Institution would be pleased to provide this service for our global standards project, but they cannot have any association with commercial providers that would be making a profit from the sale of these materials.

It seems to me that for this to be a success (meaning we actually reach those people tempted to use standards as long as it isn't too hard), we need to involve commercial vendors.  This suggests that, as kind as the Smithsonian's offer is, we should probably look for someone else to handle the material who isn't averse to associating with commercial vendors.

[Probeman]

my comments re: sulfides and metal was really focused on trace elements in standards.  These are rarely homogenous, but there is a desperate need for such in the LA-ICPMS community (et al) where matrix matching is a bigger issue.  Of course, 'pure' standards' should be pure - stands to reason, which is why I favour a good metals block over some of our 'pure' synthetic stuff (MgO is a good example of a commercially available single crystal that we've found is often not as 'pure' as all that).  Sulfides are a particular problem as noted above, and I would be pleasantly surprised if you can make a significant amount that are both 'pure' and stoichiometrically identical. 

I can imagine that some synthetic materials might be inhomogeneous in trace elements especially at ICPMS sensitivity levels, but if we start with high purity materials we might mitigate much of that, especially for EPMA where anything below a few PPM is essentially undetectable.

As for LA-ICPMS standards I agree metals or oxides would work well as primary standards. Pretty much the same situation in EPMA, though some people still haven't thought this question through sufficiently and are still seeking some trace doped standard to test their trace accuracy. The best accuracy test for trace levels is a zero blank. See here for more details:

https://probesoftware.com/smf/index.php?topic=928.msg8498#msg8498

As for testing trace accuracy in LA-ICPMS, I would similarly ask why not a (roughly) matrix matched (high purity) blank as we are (or should be!) using in EPMA?

As for commercial MgO, today it is quite easy to find MgO with close to zero Ca.  This was not true in the past. Likewise, it used to be almost impossible to find Zr without a percent or so of Hf, but this material is now available in 99.999% pure form:

https://www.americanelements.com/zirconium-metal-7440-67-7

Question: I know nothing about growing synthetic sulfides, but in talking with John Hanchar he has indicated to me that it's the purity of the starting materials that matter (and cost) the most!

I  think a lot could be done to educate current probe users about the role of standard (ahem, SJIO), background selection and instrument operating conditions which would go someway to mitigating a lot of issues (honestly, theres still papers published where dead times in olivine are hit. worrying about your standard is a little moot when that happens!).  I honestly feel the cost/benefits of this mammoth effort isn't there without embracing other microanalytical communities. Perhaps it would be worth doing a thorough market survey of demand (and not just 'I'd like some!' but 'how much would you like some?').  It may also be instructive as my gut feeling is the EPMA community at a research funding level is not in such rude health.

I agree that for many laboratories the dead time calibrations are probably a major area of inaccuracy. Paul Carpenter has tried to point this out for decades. If anyone out there is still using the "default" dead time calibrations provided to them at the time their instrument was installed, I can promise them that they have large accuracy problems. These gas detectors age quite dramatically over time and one should be re-running these dead time calibrations every year to two at most for reasonable accuracy.  This issue has actually gotten worse over time as both Cameca and JEOL have migrated to larger and larger Bragg crystals with increasing geometric efficiency.

So unless you always run a 10 nA or less, here is a link to Paul Carpenter's dead time spreadsheet which is very nice for performing your own dead time constant calculations using any software:

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

As for other microanalysis communities, we welcome all. I note that Zack Gainsforth at UC Space Sciences just wrote to Will Nachlas volunteering his TEM time, would you be willing to work with us on laser ablation standard characterization?

We need all the help we can get.

[Probeman]

2. In order to provide a long term and stable repository for these synthetic materials, we have been informed that the Smithsonian Institution would be pleased to provide this service for our global standards project, but they cannot have any association with commercial providers that would be making a profit from the sale of these materials.

It seems to me that for this to be a success (meaning we actually reach those people tempted to use standards as long as it isn't too hard), we need to involve commercial vendors.  This suggests that, as kind as the Smithsonian's offer is, we should probably look for someone else to handle the material who isn't averse to associating with commercial vendors.

Really?  I'm not opposed to having this global material hosted in several locations, but it's not just the Smithsonian, it's also NSF. I'm pretty sure NSF would not fund an effort that involves for profit activity.

Maybe once we've got a stable of high purity global standards that have been shared with the labs that actually care about accuracy, then we can have discussions with commercial providers.

[Probeman]

While discussing WDS detector dead time calibration issues someone recently made the following point which I'd like share here:

From my perspective it's exactly these sorts of instrumental calibration issues that has over time tended to corral people into finding matrix matched standards even as the matrix corrections themselves have become more accurate. As has been pointed out previously, if ones standard is exactly the same composition as ones unknown, *all* corrections are exactly 1.000!

So I think that what started out as a necessity for dealing with sub par matrix correction physics, has over the decades slowly become a crutch to avoid making sure our instruments are properly calibrated in other respects (dead time, effective takeoff, beam current linearity, etc.).

The good news is that by utilizing standards that are not exactly matrix matched, but instead accurately characterized for composition and purity, these instrumental calibration issues (and matrix correction physics) will become better understood and therefore more easily able to be improved.

[sem-geologist]

I know that high purity BaF2 and MgF2 are easily available. But with LaB6 is it high purity?  Please find out for us.

BaF2 and MgF2 are not so good EDS standards for the same reasons as La oxide-bearing phases (The Ba can emit Ma, especially if working with low voltages). Sincerely, I currently have no Ba standard which would allow to deal with this problem. One of candidates I would look for is Ba carbide (BaC2, https://www.americanelements.com/barium-carbide-50813-65-5), the same for Cs (Cs2C2) - I however have no idea how stable those would be. Currently to overcome these shortcomings I set DTSA-II to ignore M lines of Ba, but for any low voltage work that will bring huge impact on F and O EDS direct quantization.
As far of concerning LaB6 purity it needs to be pure as that is main material of that type of cathodes - any contaminants would cripple the stable emission. As from EPMA WDS perspective - I have wavescans and it is pure from that point of view.

Now When I say "wavescans" I mean very high current wavescans acquired using all available electron juice on our field emission SXFiveFE. Normally that is around 800nA and more (up to 1µA) which makes tops of peaks to blunt (unaccounted pile-up), but it exposes the backgrounds very clearly and any spectral artifacts or impurities at 10-50 ppm level is visible (depends from position and XTAL, (2048 channels 1 second per channel). The beam is defocused to 50um. The carbon coat is done with Leica coater with multi-pulse mode which makes a composite carbon layer which allows the coating to withstand 40+ minutes at these harsh conditions easily for most of standards. (Coating - this is again one of these underrated very crucial steps which if done wrongly will ruin analysis). Exception is minerals which breaks down (i.e. apatite) at this beam. I actually more believe my wavescans than some LA-ICP-MS where I have no control on fractionation, data reduction, laser stability. Lots of stuff there (at least what I had witnessed with my limited experience there) is quite a black box. And LA-ICP-MS can have all kind of nasty interference (mass interference). What I would be interested more for low concentration detection is µXRF. Don't understand me wrong, LA-ICP-MS is really robust method for comparative analysis (REE spider plot patterns, Isotope ratios, etc..), but I had never ever seen a reliable results for absolute values which would sum to 100 % (rather very far from it). Maybe there will be difference with new generation femto-second lasers, but previous generation with all that fractionation stuff is very unreliable as for absolute values, and I would take EPMA or µXRF (if done correctly) values without any doubt if would need to chose from values obtained by different methods. In that sense EPMA-WDS wavescan is quite a powerful and more reliable tool IMHO for trace detection down to tens of ppm especially when there is no interference hell (standards) and interpretation of such wavescan is simple.

Getting back on topic, as For EPMA-WDS REE I see no need of those REE borates, as REEPO4 scratch my all possible itches. (and there are also those REEP4O14, which I find less stable than REEPO4, and use it not at all). I don't know where we got these REEPO4 as they show absolutely no wavescan-detectable Pb (unfortunately, there is a very sad story behind that, why I don't know where it comes from). REE-borates would be handy for low voltage EDS, or/and substances where F, O, Na needs to be measured directly. 

Curious: why would high purity synthetic pyrite be such a bad standard material? Seems quite stable when I've used it at 30 nA and 20 keV.  Then again I usually run my standards slightly defocused or turn on the TDI correction.

Let me put Your another quote below from your previous post:

(our lab re-polishes and re-coats our standard mounts every one to two years)

If Your unknown pyrites was re-polished some weeks before EPMA session, then both your standard and Unknown pyrites are oxidized. You get away from it with 20kV generating X-rays from deeper of sample (for that reason alone I do all sulphides at 25kV). You will notice, however, that same calibrations does not give good result for chalkopyrite (even with corrected S position). That is as chalkopyrite oxidizes at different rate and extent. So basically, while your Unknown will be similarly oxidised as your standards you will get away with it, But try to do freshly polished Unknown samples and you should get some surprise.
 
How we do sulphides? as for sulphur reference we use ZnS which does not oxidizes, and does not require to be often re-polished (we re-polish our standards as You do - once a year). We don't use neither pyrite neither chalkopyrite standards as the only good correct analysis (intensity) possible to obtain from them is at first days after re-polishing of standard block. Samples of Unknown needs to be polished a day (for best results) before session. Differently than other samples, sulphide (for analysis) bearing samples are not placed into heater for riddance of water vapour, as oxidation of pyrite/chalkopyrite and other sulphides increase with temperature. We dry samples with stream of nitrogen gas, and then keep it longer in coater in vacuum to get away the vapour residual (like 1-2 hours). After coating it should not lay days on shelf (or worse in the heater) as coating is not enough to prevent pyrite from oxidation. The best it should be analysed the same day. We use Fe,Co, Ni, Cu and other metals from normal oxide standards like Fe2O3, CoO, NiO... or metals (i.e. Ag, Au) and sulphur only from ZnS. Analysis in this way closes around 100%, and most importantly the atomic composition makes complete sens. If we would try to repeat analysis after a week, there would be huge discrepancies.

From other side we need to do analysis to keep the labs running, we can't just stop everything and say we are waiting for a full set of excellent reference materials covering (near-)whole element table. 

And no one is saying we have to stop all current lab work immediately until this project is complete. Where did you see that mentioned in the open letter?   

These are inner personal regrets sometimes. Especially when looking to some mine, one of the first analysis which were published. At least I find myself pretty often in situation when I am asked for results immediately! Even if there are some clear analytical biases or artifacts (which were not obvious previously), which would imply to redo some analysis at changed settings. Not everyone would say "Ok, take time and investigate and make sure these next analyses are correct, or redo those and make it more correct", rather "We already published this paper with these standards and these settings, we don't want to describe new methodology, we just will cite that old one, we don't ***** care... it should be completely the same. Period!", because our system is publish-or-perish, and incremental improvement of method does not fit well with that system.

So that is why I wish to have synth's covering all elements already yesterday. Of course I understand that it will take time.

I am reminded of occasions when I have been contacted by some EPMAers attempting to utilize the MAN background correction (Donovan et al, 2017), and been told that they had no idea that their standards were so contaminated with minor and trace elements...   

That is why I don't use MAN, but single background and precise and universal slope - This way I can get down to 10 ppm, but without: any hassle of LA-ICP-MS of standards, making background correction curves, etc. Simple, elegant, reliable, works same independently from matrix.
 

So the plan is that these materials will be provided for free to qualifying laboratories. A good first step in that qualification process is to join the FIGMAS:

https://figmas.org/about.php

Do I understand correct, I should join at first MicroAnalysis Society (MSA, as European joining MAS would make little sense), then I  should join FIGMAS?

As dead time was picked few times... I probably should get back and finish my MC simulation of pile-ups and come up at last with non-linear equation which actually works for whole range of possible count rates (0-1Mcps), and different generation of counting electronics.

[Probeman]

If anyone is interested in our current Google spreadsheet of commercially available synthetic standard material candidates, as shown here:



Please use this link:

https://docs.google.com/spreadsheets/d/19AeXvxIaP6qvChbE7cxK05B_6rkZSN14T-7ZJ7nkm8M/edit*gid=0

If you would like to add to this spreadsheet any additional commercial (or academic or institutional) sources of potential synthetic standard candidates, please contact Nicholas Ritchie and he can add your email to the approved  "edit list".  Please read the instructions carefully so this spreadsheet remains well  organized.

Ultimately we are looking for high purity synthetic materials in 500 to 1000 gram quantities, enough for true global standards with extra material for future generations. This material does *not* need to be crystallographically oriented or polished. Also these do not need to be single crystals, they can be broken in pieces as long as the individual crystals are at least millimeter(s) in size.

We're looking for: Mg2SiO4, YAG, RbTiOPO4, KTiPO4, MnO, Fe3O4, NiO, ZnO, LaAlO3, MnPSe3, LiTaO3, 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 and sulfosalts, etc., etc.

We would like pricing on 500 to 1000 gram amounts and also, for some initial testing, pricing on amounts in the range of 3 to 5 grams.

We need your help in tracking down suitable materials!