How to Read a Peptide Certificate of Analysis (COA)
This article is educational information for a laboratory audience. It is not medical advice and not a recommendation for human use. Peak Labs products are supplied for laboratory research use only. Sources are cited at the end.
A Certificate of Analysis is the one document that tells you what is actually in the vial. Everything else on a product page is a claim. The COA is evidence. If you buy research peptides, reading one properly is the difference between working with a known compound and guessing.
Here is how to read a peptide COA, section by section, and how to spot one that was made to look convincing rather than to be true.
Who should issue the COA
Start with the letterhead. A COA carries weight when an independent third-party laboratory produced it, not the seller. A supplier grading its own product has an obvious conflict of interest. An outside lab has none. Reputable analytical labs in this space include Janoshik Analytical, which runs the testing behind every Peak Labs batch. If a supplier shows no third-party report at all, treat the purity number as marketing.
The four things a COA has to establish
A complete certificate answers four questions:
- Identity. Is this the compound on the label?
- Purity. What fraction of the material is the target compound?
- Contaminants. Are heavy metals or other residues within limits?
- Traceability. Does the report tie to the exact batch you receive?
Miss any one and the certificate is incomplete. Work through them in order.
Reading the purity result (HPLC)
Purity comes from High-Performance Liquid Chromatography. The instrument separates a sample into its components and plots them as a chromatogram, a graph of detector signal against time. Each peak is a compound leaving the column. The tall main peak is your target.
Purity is that main peak's share of the total peak area: main peak area divided by the area of all peaks, times 100. A report of 99% means the target accounts for 99% of the detected material. Most reputable research-grade suppliers work to 98% or higher, which suits cell-culture and animal research where reproducibility matters and confounds have to stay low.
Look for the actual chromatogram image, not just a typed number. A real report shows the trace, the retention time, and the integration. A bare "99%" with no chromatogram is a claim wearing a lab coat.
Reading the identity result (mass spectrometry)
HPLC tells you how pure the sample is. It does not tell you what the sample is. A peptide missing a single amino acid can still show 99% on HPLC and be the wrong molecule. Identity needs mass spectrometry.
Mass spectrometry measures molecular weight. The COA should list two numbers: the theoretical molecular weight calculated from the sequence, and the observed molecular weight the instrument measured. A good report states both and confirms they match within tolerance. On a modern LC-MS/MS instrument, mass accuracy sits within a few parts per million.
This is also where a subtle fake shows itself. If the report states mass-spec agreement only at a loose tolerance such as plus or minus 0.1%, do the arithmetic. On a 3,000-dalton peptide, 0.1% is a 3-dalton window, wide enough to hide a truncated sequence or a swapped residue. Tight tolerance is a feature, not a formality.
Reading the contaminant screen (heavy metals)
Synthesis and handling can leave metal residues. A heavy-metals screen by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) reports those levels against the batch. Not every compound ships with one, but its presence is a sign the lab took the sample seriously.
Checking traceability
The report has to belong to your material. Match the lot or batch identifier on the certificate to the number printed on the vial. A COA for "a" batch is not a COA for "your" batch. Reputable suppliers publish per batch and mark a new batch as in progress until its report returns, rather than reusing an old one.
The red-flag checklist
Reject or question a COA if any of these are true:
- No third-party lab named; the seller tested itself.
- A purity percentage with no chromatogram image behind it.
- No mass-spec result, or a mass tolerance loose enough to hide sequence errors.
- The compound name or molecular weight on the report does not match the product.
- No lot or batch identifier, or one that does not match the vial.
- A single certificate reused across every batch and every product.
How Peak Labs publishes COAs
Every Peak Labs batch is analysed by Janoshik Analytical: HPLC for purity, ICP-MS for a heavy-metals screen where it applies. We publish the real reports per batch. Open any product page and select Certificate of Analysis to view or download the report for that compound, or read the method summary on our Certificate of Analysis and third-party testing page. Browse the tested catalogue in all research compounds.
For the deeper mechanics of the two tests and why you need both, read HPLC vs mass spectrometry.
Sources and further reading
- United States Pharmacopeia (USP), general chapters on chromatography and purity by area normalization. usp.org
- IUPAC, definitions and recommendations for mass spectrometry terms. iupac.org
- PubChem (NIH) for compound identity and theoretical molecular weight. pubchem.ncbi.nlm.nih.gov
- NIST Chemistry WebBook for reference mass data. webbook.nist.gov
Research use only. Peak Labs products are supplied strictly for in-vitro laboratory research. They are not medicines or supplements, are not for human or veterinary use, and are not intended to diagnose, treat, cure, or prevent any condition. Nothing here is medical advice.