How to read a certificate of analysis
A COA is the only objective evidence you have about what is in a vial. Most of the document is boilerplate; four lines actually matter.
HPLC purity
High-performance liquid chromatography separates the sample into its components. The purity figure is the target peak's area as a percentage of all peaks. Anything at or above 98% is normal for research-grade material. Look at the chromatogram itself, not just the number — one clean dominant peak is what you want to see.
Mass spectrometry identity
HPLC tells you how pure the sample is. Mass spec tells you whether it is the right molecule at all. The observed mass should match the theoretical molecular weight closely. A pure sample of the wrong compound is worthless.
Batch number and date
The batch number on the certificate must match the batch printed on your vial. A generic certificate with no batch reference, or one dated years earlier, tells you nothing about what you received.
Which laboratory issued it
An independent third-party laboratory letterhead carries weight. A certificate issued by the seller does not, however well designed it is.
Red flags
Purity quoted as exactly 99.9% on every product. No chromatogram image. No batch number. A PDF that is an image rather than text, making the numbers unverifiable.