Research guide

How to Read a Peptide Certificate of Analysis (COA)

Quick answers

What is a COA?
A certificate of analysis is a lab report on one specific batch. It lists the tests run, the methods used and the results.
What are the two numbers that matter most?
Purity, usually by HPLC, and identity, usually by mass spectrometry. Purity says how much of the sample is the main compound. Identity says whether the main compound is the right molecule.
How do I know the COA belongs to my vial?
The lot or batch number on the COA must match the lot number printed on your vial. If it does not match, the COA tells you nothing about your vial.
Is third-party testing better than in-house?
Usually, yes, because the lab has less reason to shade the result. But only if you can confirm the lab exists and the report is real.
What are the red flags?
No lot number, a lot that does not match, the same COA reused across products, missing dates, no lab name, no chromatogram or spectrum, and edits or blur around the numbers.

A certificate of analysis, or COA, is the single most useful document a research peptide supplier can give you. It is also one of the easiest to fake or misuse. This page explains what each part of a peptide COA means, how to check that it actually describes the material in your hands, and the warning signs that it does not.

For the bigger picture of what a COA can and cannot prove, see our brief What a Certificate of Analysis Tells You (and What It Can't). Research peptides are for research use only and are not for human consumption.

The parts of a peptide COA

Header details

A real COA should show:

  • Product name and sequence or catalog number.
  • Lot or batch number. This is the key that links the report to a physical vial.
  • Test date and, ideally, a manufacturing date and a retest or expiry date.
  • Lab name, address and contact details.
  • A signature or approval by a named role, such as a QC manager.

Purity by HPLC

HPLC stands for high-performance liquid chromatography. The sample is pushed through a column that separates its components. A detector draws a graph called a chromatogram, with peaks for each component. Purity is usually reported as the main peak's share of the total peak area, for example "98.6%."

What to look for:

  • The chromatogram itself, not just a number. A single number with no graph is much weaker.
  • The method details: column type, wavelength, and run conditions.
  • A main peak that is clearly dominant, with small labeled impurity peaks.

Keep in mind what HPLC purity is not. It does not tell you what the other few percent are. And it is a relative measure. It does not say how much peptide is in the vial by weight.

Identity by mass spectrometry

Mass spectrometry (MS) measures the mass of molecules in the sample. For a peptide, the expected mass can be calculated from its sequence. The COA should show the expected mass and the observed mass, and they should agree closely. Look for the actual spectrum, not just a "conforms" checkbox.

HPLC can tell you a sample is 99% one thing. MS tells you whether that one thing is the right thing. You want both.

Other tests you may see

  • Net peptide content. How much of the powder is peptide versus salts and water. This matters for concentration math.
  • Water content, often by Karl Fischer titration.
  • Endotoxin, a measure of bacterial contamination residue.
  • Appearance, such as "white lyophilized powder."

Matching the COA to your vial

This is the step most people skip, and it is the most important. A COA describes one batch. If your vial came from a different batch, the COA is about someone else's material.

  1. Find the lot number printed on your vial or its box.
  2. Find the lot number on the COA.
  3. They must be identical. Not similar. Identical.
  4. Check that the product name, quantity and dates make sense together. A test date after the shipping date, or years before the product was listed, is a question to ask.

A supplier that posts a single "sample COA" for a product, with no way to get the report for your specific lot, is giving you marketing, not verification.

Third-party versus in-house testing

An in-house COA comes from the manufacturer's or seller's own lab. A third-party COA comes from an independent testing lab. Independent testing is generally more credible because the lab has no direct stake in the result.

But "third-party" is only worth something if you can check it:

  • Does the named lab exist, with a real address and website?
  • Does the lab offer a way to verify a report, such as a report ID or lookup?
  • Does the report format match other reports from that lab?

If you cannot answer those, the label "third-party tested" is just a phrase.

Red flags of fake or reused COAs

  • No lot number, or a lot number that does not match your vial.
  • The same COA used across different products or across years of sales.
  • Round, suspiciously perfect numbers with no chromatogram or spectrum behind them.
  • Missing lab identity: no name, address or contact.
  • Signs of editing: mismatched fonts, blurred areas around numbers or dates, pasted logos.
  • An observed mass that does not match the expected mass for the sequence.
  • "COA available on request" that never arrives.

Why this matters: what testing has found

Labels can be very wrong. In a 2024 study, researchers made test purchases of semaglutide from illegal online sellers and analyzed what arrived. The vials' labels claimed 99% purity. Measured purity ranged from about 7.7% to 14.4%. Endotoxin was detected in every sample. Several ordered products never arrived at all. That study looked at one compound from one type of seller, so it does not describe every supplier. But it shows how far a label can drift from what is in the vial, and why a lot-matched, verifiable COA matters.

Next, see How to Tell If a Research Peptide Company Is Legit for the full supplier checklist.

Sources

  1. Ashraf AR, Mackey TK, Vida RG, et al. Multifactor quality and safety analysis of semaglutide products sold by online sellers without a prescription. J Med Internet Res. 2024;26:e65440. PubMed 39509151 · DOI
  2. U.S. Food and Drug Administration. 21 CFR Part 211, Current Good Manufacturing Practice for Finished Pharmaceuticals (eCFR). Source

Peptide Proof reports what studies found. Research peptides are for research use only and are not for human consumption. Nothing on this page is medical advice, dosing guidance or a treatment recommendation.

Where to buy: researchers who want materials with a certificate of analysis can see our sourcing partner, Trynx Research.