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I used to work in a lab that bought mud from NIST. We were measuring soil contaminants, and needed a calibration point for the data collected. So, whenever we

I used to work in a lab that bought mud from NIST. We were measuring soil contaminants, and needed a calibration point for the data collected. So, whenever we collected data from river mud, we also ran the NIST mud. That way, any drift in our experimental setup over time could be normalized out.

edrxty 4y ago
Ok, I gotta ask. How does NIST source a large supply of mud that's stable in composition over a long period of time, both in terms of supply chain and storage? That seems to be the case for a lot of these items. Either they have a process for making these products with sourced ingredients that are somehow hyper stable or they buy up 1000lbs of breakfast cereal, grind it into powder, then vacuum seal and freeze it in a vault somewhere alongside powdered sewage, all the time assuming nobody in the future of the planet will need more than 1000lbs of reference powdered breakfast cereal total.
- voxadam 4y ago
  As I understand it, each and every sample isn't necessarily uniform bur rather each sample is characterized and qualified by a NIST lab and a certificate of analysis (COA) is supplied with each sample. This allows tier 2 and lower labs to verify that their equipment and analyses are within spec.
  - samatman 4y ago
    There are exact standards both for the accuracy of the reference material and the precision of the COA. So NIST can work backward, using faster tests to confirm that the material has suitable qualities to represent, say, 2% milk, then take the precise measurements for the actual batch of sample, which of course will vary.
- zinekeller 4y ago
  > Ok, I gotta ask. How does NIST source a large supply of mud that's stable in composition over a long period of time, both in terms of supply chain and storage? Technically, they don't. Obviously, they have some storage (this is one of those things you don't want to use just-in-time manufacturing). Instead, NIST (and other analogous standards organisations) have batches of materials and really, really expensive machines (that are hard to mass-produce) that can measure out the precise quantities of whatever thing they need to measure backed by processes that intrinsically is just precise (and accurate, for pedants), for example, electron microscopes or atomic force microscopes, which is then used by others (like in this case for measuring mud) to machines that are easy to mass-produce but can measure badly if not checked regularly. For some things though (like drug testing in urine), they instead have a pure substance laced with precise amounts of substances you've expect to find, but that's relatively easier than most SRMs where you're measuring things you've already have (whether it's mud, crude oil, whale blubber or peanut butter).
  - deleted 4y ago
    [deleted]
- thatguy0900 4y ago
  https://www.si.com/mlb/2019/08/07/baseball-mud-rawlings https://www.si.com/mlb/2019/08/07/baseball-mud-rawlings fun story about consistent mud collecting for the mlb
- MereInterest 4y ago
  So, starting with an analogy. Suppose you want to know the distance from Grand Central Station in New York City to a cafe a block from the Eiffel Tower. You have two options of how to make the measurement. Option 1 is to directly measure the distance. Option 2 is to use a known distance between Grand Central Station and the Eiffel Tower, then add the distance from the Eiffel Tower to the cafe. Option 1 has fewer dependencies, but Option 2 is much easier and (assuming your reference measurement is correct) will give a much more accurate measurement. Similarly, any time you're making a high-precision measurement, you want to make it relative to something that's already known to a high precision. It doesn't need to be the same high-precision measurement each time, so long as it's something that gets you into the same ballpark as the thing you're measuring. That way, you don't need to make an absolute measurement, but only need to make a relative measurement. For the mud samples, we didn't actually care that it was the example same elemental composition in the handful of NIST samples we had, only that it had a known amount of the trace elements we were measuring. That way, instead of needing to explicitly measure detector efficiency, everything became a very simple scaling question of "(X counts in sample) / (Y counts in reference) * (Z known trace element in reference)".

edrxty 4y ago

Ok, I gotta ask. How does NIST source a large supply of mud that's stable in composition over a long period of time, both in terms of supply chain and storage? That seems to be the case for a lot of these items. Either they have a process for making these products with sourced ingredients that are somehow hyper stable or they buy up 1000lbs of breakfast cereal, grind it into powder, then vacuum seal and freeze it in a vault somewhere alongside powdered sewage, all the time assuming nobody in the future of the planet will need more than 1000lbs of reference powdered breakfast cereal total.

voxadam 4y ago
As I understand it, each and every sample isn't necessarily uniform bur rather each sample is characterized and qualified by a NIST lab and a certificate of analysis (COA) is supplied with each sample. This allows tier 2 and lower labs to verify that their equipment and analyses are within spec.
- samatman 4y ago
  There are exact standards both for the accuracy of the reference material and the precision of the COA. So NIST can work backward, using faster tests to confirm that the material has suitable qualities to represent, say, 2% milk, then take the precise measurements for the actual batch of sample, which of course will vary.
zinekeller 4y ago
> Ok, I gotta ask. How does NIST source a large supply of mud that's stable in composition over a long period of time, both in terms of supply chain and storage? Technically, they don't. Obviously, they have some storage (this is one of those things you don't want to use just-in-time manufacturing). Instead, NIST (and other analogous standards organisations) have batches of materials and really, really expensive machines (that are hard to mass-produce) that can measure out the precise quantities of whatever thing they need to measure backed by processes that intrinsically is just precise (and accurate, for pedants), for example, electron microscopes or atomic force microscopes, which is then used by others (like in this case for measuring mud) to machines that are easy to mass-produce but can measure badly if not checked regularly. For some things though (like drug testing in urine), they instead have a pure substance laced with precise amounts of substances you've expect to find, but that's relatively easier than most SRMs where you're measuring things you've already have (whether it's mud, crude oil, whale blubber or peanut butter).
- deleted 4y ago
  [deleted]
thatguy0900 4y ago
https://www.si.com/mlb/2019/08/07/baseball-mud-rawlings https://www.si.com/mlb/2019/08/07/baseball-mud-rawlings fun story about consistent mud collecting for the mlb
MereInterest 4y ago
So, starting with an analogy. Suppose you want to know the distance from Grand Central Station in New York City to a cafe a block from the Eiffel Tower. You have two options of how to make the measurement. Option 1 is to directly measure the distance. Option 2 is to use a known distance between Grand Central Station and the Eiffel Tower, then add the distance from the Eiffel Tower to the cafe. Option 1 has fewer dependencies, but Option 2 is much easier and (assuming your reference measurement is correct) will give a much more accurate measurement. Similarly, any time you're making a high-precision measurement, you want to make it relative to something that's already known to a high precision. It doesn't need to be the same high-precision measurement each time, so long as it's something that gets you into the same ballpark as the thing you're measuring. That way, you don't need to make an absolute measurement, but only need to make a relative measurement. For the mud samples, we didn't actually care that it was the example same elemental composition in the handful of NIST samples we had, only that it had a known amount of the trace elements we were measuring. That way, instead of needing to explicitly measure detector efficiency, everything became a very simple scaling question of "(X counts in sample) / (Y counts in reference) * (Z known trace element in reference)".