General EPMA > EPMA Standard Materials

An Open Letter to the Microanalysis Community

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sem-geologist:
High purity and high quality synthetic substances... Where should I sign?   8)

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:

--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---High purity and high quality synthetic substances... Where should I sign?   8)

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

--- End quote ---

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


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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).

--- End quote ---

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...


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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.

--- End quote ---

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!   :D


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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.

--- End quote ---

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.


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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.

--- End quote ---

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.


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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. 

--- End quote ---

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.


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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:

--- End quote ---

Good for you. I wish all labs worked so diligently on their standard materials.  8)

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...   :(


--- Quote from: sem-geologist on November 22, 2021, 03:33:06 AM ---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?

--- End quote ---

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?

NicholasRitchie:

--- Quote ---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.
--- End quote ---
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.

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