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What a Certificate of Analysis actually tells you

2 min read

A Certificate of Analysis is the document a testing lab produces for a specific batch of material. It is the difference between a supplier claiming purity and a supplier demonstrating it — but only if you can read one.

Identity

Before purity means anything, the material has to be the right compound. Identity is usually confirmed by mass spectrometry, reported as an observed molecular weight compared against the theoretical value. Those two numbers should agree closely. A COA reporting purity without confirming identity has answered the second question and skipped the first.

Purity

Typically determined by HPLC and reported as a percentage — the share of material that is the intended compound rather than anything else. Look for the method and wavelength alongside the number. A bare percentage with no method attached is an assertion, not a measurement.

Mass

How much material is actually in the vial. This matters more than it sounds: a vial labeled 10 mg containing 8 mg is a 20% discrepancy in every calculation downstream.

Residual solvents and water

Synthesis and purification leave traces behind, and lyophilized powders absorb moisture. Both displace mass. A result that reports purity but not water content leaves an open question about what the remaining percentage consists of.

A COA without a batch number is not a certificate of analysis. It is a brochure.

Batch identity and date

The document must name the specific lot it describes and when it was tested. Without that link, the certificate cannot be tied to the vial in your hand — and a generic COA reused across production runs tells you nothing about the material you actually received.

One habit worth adopting: check whether the testing laboratory is named and independent of the supplier. In-house results are not worthless, but they are not the same claim.

Research use only. The compounds discussed here are supplied for laboratory research purposes exclusively. They are not drugs, dietary supplements, or cosmetics, and are not intended or approved for human or veterinary use. This article is a summary of published chemistry and pharmacology, provided for reference. It is not guidance for use in any living subject.