What a COA is for
A Certificate of Analysis (COA) is the document that turns a vial of material into a characterized, reproducible input for in vitro work. It records what the material is, how pure it is, how that was measured, and which specific lot the result applies to.
For a bench scientist, the COA is the difference between trusting a label and trusting a measurement. Reading one correctly means checking four things: identity, purity, method, and lot linkage.
Identity and purity are separate claims
Identity answers "what is this molecule?" — confirmed by sequence, molecular weight, or structure. Purity answers "how much of the sample is that molecule?" — reported as an HPLC area percentage. They are independent, and both matter.
A material can be highly pure but the wrong molecule, or the right molecule at low purity. A complete COA reports both, with the method that produced each number.
- Identity: mass spectrometry (ESI-MS / MALDI-TOF) or amino acid analysis.
- Purity: reversed-phase HPLC area normalization.
- Content: the amount of target peptide present, distinct from gross fill.
What to check on every COA
Match the lot number on the certificate to the lot number on the vial. Confirm the testing laboratory is named, the test date is present, and the method parameters are stated rather than assumed.
- Lot / batch number and a link to the specific production batch.
- Named laboratory and test date.
- Method details (column, wavelength, gradient) — not just the result.
- Out-of-spec or non-reportable values, if any.
Red flags to look for
A COA that is recycled across many products, has no lot linkage, names no laboratory, or omits method parameters should be treated with skepticism. Documentation that cannot be traced to a specific batch does not de-risk an experiment.
- Generic or identical COAs across different materials.
- Missing or ambiguous lot linkage.
- Unnamed laboratory or no test date.
- Purity claimed with no analytical method.