If you've spent any time comparing research suppliers, you've seen the phrase "99% pure" stamped on nearly every product page. The number on its own means very little. What matters is who tested it, how, and whether the report matches the vial in your hands.
Here's how to read a Certificate of Analysis like a lab manager would.
1. Check who ran the test
An in-house COA is a starting point, not proof. Look for an independent, named laboratory, ideally one you can contact to verify the report. If the lab name is missing or generic, treat the document as marketing.
2. HPLC tells you purity, not identity
High-performance liquid chromatography separates a sample into its components and shows how much of it is the main peak. A clean chromatogram with one dominant peak is a good sign, but HPLC alone can't confirm the compound is what the label says.
3. Mass spec confirms identity
Mass spectrometry measures molecular weight. If the observed mass matches the theoretical mass for the compound, you have reasonable confirmation of identity. The best suppliers publish both HPLC and MS for every batch.
A purity number without an identity test is half a report.
4. Match the batch number
A COA should reference a specific lot. If the report is undated, unbatched, or reused across every product, it isn't telling you anything about the material you'd actually receive. Before ordering, you can browse their published test results and check that lot numbers line up.
5. Red flags to watch for
- Purity listed with no chromatogram attached
- The same COA image used for multiple compounds
- No lab name, address, or report ID
- Reports only available "on request" after purchase
The bottom line
Documentation is the cheapest quality filter you have. A supplier that publishes batch-specific, independently verified HPLC and MS results up front is doing the work you'd otherwise have to do yourself.