A Certificate of Analysis (COA) is a document issued by a testing laboratory that reports the measured identity and purity of a specific batch of material. For research peptides, it is the main way a buyer can confirm that a vial contains what the label says.
Without a COA, a researcher has only the seller's word. With one, there is a record from a lab that tested the material directly.
What a COA usually includes
Most peptide COAs list the compound name, the batch or lot number, the date of analysis, the name of the testing lab, the methods used and the results.
The two most common methods are HPLC (high-performance liquid chromatography), which measures purity, and mass spectrometry (MS), which confirms identity by molecular weight. Some reports also include a measured quantity per vial, plus extra panels such as heavy metals, endotoxin, sterility or contaminant screening.
Why the lot number matters
A COA only describes the batch it was run on. Peptides are made in batches, and each batch can turn out slightly differently. Matching the lot number on the report to the lot on your vial is the simplest check that the report applies to your material.
Be cautious of a COA with no lot number, or one that is several years old and reused for every batch.
Independent vs. in-house testing
Reports from an independent, third-party lab carry more weight than in-house testing, because the lab has no stake in the result. Every report in our COA Library comes from an outside lab.
How to check a COA
Look for the lab's name and contact details, the date, and the lot number. Many labs offer a verification code or online lookup so you can confirm the report is genuine.
Check that the compound and amount match what you bought. Then look at the purity figure and the mass spec result to make sure both are reported.
Red flags
Watch for missing lab details, blurry or edited-looking documents, purity listed with no method, no identity test, or a report that does not match the product size. When in doubt, contact the supplier and ask for the original report.