Reading a lab report
What a certificate of analysis (COA) for a peptide should show, how to read its main numbers, and the red flags. No vendors are named.
What a COA is
A certificate of analysis is a lab’s report on one batch, identified by its lot number. It should match the lot printed on your vial, name the lab and the test methods, and carry a date. A COA describes the sample that was tested, not what happened to the vial in storage or shipping since.
What it should cover
FDA’s 2026 reviews of peptides nominated for compounding looked for these tests on certificates of analysis, and called sterility, endotoxins and microbial counts critical for injections.
| Test | What it tells you |
|---|---|
| Identity (mass spectrometry) | That the molecule is the one on the label. The measured mass should match the molecular weight on the compound’s datasheet here. |
| Purity (HPLC) | What share of the peptide material is the target peptide, as a percentage of peak area. It says nothing about how much peptide is in the vial. |
| Assay (content) | How much peptide is actually present. Powder also holds water and salt, so a “5 mg” vial can hold less than 5 mg of peptide. |
| Impurities and aggregates | Related peptides left over from synthesis, and clumped peptide. FDA ties both to the risk of immune reactions with injections. |
| Bacterial endotoxins | Fragments of bacteria that cause fever and inflammation even in a sterile product. Reported in endotoxin units (EU), by the bacterial endotoxins test. |
| Sterility or microbial count | Whether living microbes are present. Sterility and endotoxins are separate tests; passing one doesn’t cover the other. |
Salts and water change the weight
Many peptides are sold as acetate or trifluoroacetate (TFA) salts. FDA gives TB-500 as 889.0 g/mol on its own and 949.1 g/mol as the acetate salt, so about 6% of the salt’s weight isn’t peptide, before any water is counted. When a COA reports net peptide content, that’s the share of the powder that is peptide.
Compare: the TB-500 datasheet lists 889.0 g/mol for the peptide itself.
Red flags
- No lot number, or one that doesn’t match your vial.
- No lab name, method or date.
- Only purity is reported. FDA found a public COA for TB-500 that listed appearance, identity and purity, with no assay, impurities, endotoxin or aggregate testing.
- Identity shown only by HPLC. A matching HPLC time suggests identity; mass spectrometry confirms it.
- The same COA shown for different batches, or results with no chromatogram or spectrum behind them.
- An injectable with no endotoxin or sterility result.
What a COA can’t do
A clean report shows that one sample passed the tests listed. It doesn’t make an unapproved product safe, effective or legal to use, and it can’t vouch for the vial in your hand if the lot differs or the product was stored badly.
Sources: FDA Pharmacy Compounding Advisory Committee briefing documents (December 2024 and July 2026); USP general chapters 85 (bacterial endotoxins test) and 71 (sterility tests).