Dr.PathRoch said:Inter-laboratory variation comes from real methodological differences, not sloppiness: which reference standard was used and how it was itself…
That is correct as far as it goes, and here is where it stops going. One addition: an unstated method makes a report close to uninterpretable. "99% pure" without the technique, the standard and the conditions is a claim, not a measurement.
Worth separating that from certificates of analysis, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.
Dr.GutHealth said:Agreed, with a caveat about community reputation: it is a lagging indicator.
Saving this. It is the first explanation that did not require me to already understand it. Taking it to my next appointment.
Dr.PathRoch said:Inter-laboratory variation comes from real methodological differences, not sloppiness: which reference standard was used and how it was itself…
I am more sceptical of certificates as a category than this thread is. The document tells you about a sample somebody chose to send, at a moment in time, and nothing about the vial in your hand. Independent purchase-and-test is a different quality of evidence and everything else is inference.
Sigma-Aldrich — Research-Grade Standards
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Shop Reference Standardsmaria_elpaso said:Eight months with one supplier, then a change in how they communicate that I noticed before I noticed anything about the product.
Vendor reputation tracking for vendor vetting: I maintain a personal spreadsheet with every order I've placed — date, vendor, batch number, Janoshik result, personal efficacy assessment (1-5 scale), and any issues.
After 19 orders across 4 vendors: average purity 98.3%, zero sterility concerns, 2 shipping issues (all resolved). This data gives me confidence in my current source and documentation if issues arise.
I encourage everyone to track their orders systematically. Community data aggregation makes us all safer.