How to Read a Peptide COA (Certificate of Analysis): What It Is and How to Verify It

Key takeaways

A Certificate of Analysis (COA) is the primary evidence a laboratory has about the identity, purity, and quantity of the material in a vial. For a research peptide, it is also the single most useful document for judging whether a supplier is trustworthy. This article walks through what a real COA contains, what each measurement actually tells you, and the specific red flags that indicate a document is decorative rather than diagnostic.

What a COA is

A COA is an analytical report produced by a laboratory that received a sample of a specific batch and ran a defined set of tests on it. For research peptides, "real" COAs are produced by independent third-party analytical laboratories — organisations whose business is analytical chemistry and who have no commercial stake in the outcome of the test. Two labs commonly seen in this space are Janoshik Analytical and Freedom Diagnostics (see the published certificates). Both are examples of independent labs; both publish reports that can be verified against the issuing lab's system.

A COA that is generated by the seller and never touched by an independent lab is not third-party. It is a claim.

The methods you should see: HPLC and MS

A competent peptide COA reports at least two techniques.

High-Performance Liquid Chromatography (HPLC)

HPLC separates the components of a sample by pushing them through a chromatographic column under high pressure. Each component elutes at a characteristic time and produces a peak on the chromatogram. Peak areas are integrated, and the reported "purity %" is typically the area of the main peak divided by the total peak area (area-percent).

What area-percent tells you: how much of what the UV detector saw at that wavelength was the peptide of interest, versus other UV-absorbing species (fragments, side-products, residual reagents).

What area-percent does not tell you: it is not a mass fraction. Non-UV-absorbing impurities (residual salts, water) are largely invisible to a standard HPLC-UV method. A 99% area-percent number is not the same as "99% of the powder in the vial is peptide."

Mass Spectrometry (MS)

MS confirms identity. The instrument measures the mass-to-charge ratio (m/z) of ions produced from the sample. A real peptide COA will report a measured mass that matches the theoretical monoisotopic or average mass of the target peptide, usually to within a fraction of a Dalton for a well-calibrated instrument. Common ionisation methods are ESI (electrospray) and MALDI.

What MS tells you: whether the main peak on the HPLC really is the peptide it claims to be.

Without MS, a high HPLC purity number is not enough — the main peak could, in principle, be the wrong peptide entirely.

Reading a real report end-to-end

When you open a peptide COA, look for the following:

1. The issuing laboratory's name, address, and report identifier. A real report is issued by a real company at a real address, with a unique report number you can quote back to them.
2. The sample identifier and lot / batch number. Every vial on the supplier's shelf should be traceable to a lot; every lot should be traceable to one specific COA.
3. Analytical methods. The report should name the techniques used (e.g. RP-HPLC with UV detection at a specified wavelength; ESI-MS in positive mode). Vague reports that just say "purity: 99%" without stating how are less informative than they look.
4. The chromatogram itself. A real report includes the chromatogram image. You should be able to see the main peak, retention time, and integrated peak table.
5. The mass spectrum. A real report includes the mass spectrum with the observed m/z and the assigned charge state, and states the theoretical mass for comparison.
6. Date of analysis. COAs are batch- and time-specific. A report from three years ago on a different lot number tells you very little about the material you actually received.

What "purity %" actually measures

Restated as a checklist for a reader:

• Purity is usually area-percent by HPLC-UV at a stated wavelength.
• It captures UV-absorbing impurities relative to the main peak.
• It does not capture residual salts, moisture, counter-ions, or anything else the detector does not see.
• A high purity number is meaningful only alongside a mass-spectrum confirmation that the main peak is the intended peptide.

A COA that lists a purity number without either a chromatogram or a mass spectrum is not giving you enough information to act on.

Red flags

Some patterns should make a researcher pause:

• No lot number. Without a lot, the COA is not tied to the material in the vial.
• No issuing laboratory name. "Independently tested" with no lab named is not independent.
• Self-reported purity. A number that appears only on the seller's marketing page and never on a lab report.
• A single COA re-used across every product. Real batches produce real, distinct reports.
• No chromatogram, no spectrum. A purity number that is not backed by the underlying data.
• A COA older than the manufacturer's stated shelf-life for that lot.
• PDFs that have clearly been edited — different fonts inside the same table, misaligned rows, watermarks that don't belong to the lab.

Verifying a COA

The strongest form of verification is checking the report against the issuing laboratory's own system. Independent labs like Janoshik Analytical and Freedom Diagnostics maintain report databases you can query with the report identifier. If the number on the paper matches a record on the lab's system, the document is genuine. If it does not match, or the lab has no record, that is the entire story.

At Hermetica, every published third-party report is listed on the Certificates of Analysis page with the issuing lab and batch reference so a researcher can perform this check directly.

A COA read this way — methods, lot, chromatogram, spectrum, verification — is what makes a research peptide a defensible reagent rather than an act of faith.

Working through certificates for a Canadian order? Our peptides Canada catalogue marks which SKUs carry a published third-party COA, and the TB-500 10mg listing links its full Janoshik report.

Worked examples of every field described above appear on the certificates we publish. The full set is in the COA library, and each lot is linked from its product page — see BPC-157 or MOTS-c for a current example.

Peptide COA questions, answered briefly

What does COA mean for peptides?

COA stands for certificate of analysis. For a peptide it is the testing laboratory's report on a sample from one batch, giving identity (usually by mass spectrometry), purity (usually by HPLC), the method and the date.

How do COAs verify peptide purity?

They report the HPLC area-percent of the main peak. D'Hondt et al. (2014) list the peptide-related impurities that synthesis can leave, including deletion and insertion sequences, racemised residues, side-chain adducts, oxidation products and dimers. HPLC separates many of these from the main peak, and that ratio is the purity figure.

What does a COA not cover?

Counter-ion content. Peptides made by solid-phase synthesis are mainly obtained as trifluoroacetate salts (Roux et al. 2008), and Erckes et al. (2025) argue that TFA content should be analysed and stated separately. If the certificate is silent on counter-ions, so is the purity number.

Worked example from the Hermetica library

Related: what is BPC-157, what is TB-500, how to test peptide purity, Janoshik peptide COA checklist, what 99% purity means.

FAQ

What is a COA for peptides?

A certificate of analysis: a report from a testing laboratory stating the identity, purity and test method for one specific batch of a peptide. It describes only the lot that was sampled.

How do you read a peptide COA?

Check five things in order: the issuing laboratory and test number, the batch number, the method (HPLC for purity, mass spectrometry for identity), the reported purity, and the test date. The batch must match the vial.

How do you verify a peptide COA is authentic?

Look up the test number on the issuing laboratory's own verification system and confirm that the compound, batch and purity match the PDF. A report the lab has no record of should not be relied on.

Does a COA show how much peptide is in the vial?

Usually not. HPLC purity is a ratio of UV-detected components, not a mass. Counter-ions such as trifluoroacetate are measured separately, as Roux et al. (2008) and Erckes et al. (2025) describe.

What impurities does a COA purity figure cover?

Peptide-related impurities that HPLC separates from the main peak, such as deletion and insertion sequences, racemised residues and oxidation products. D'Hondt et al. (2014) review these impurity types in synthesised peptides.

References

1. D'Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, De Spiegeleer B. (2014). Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis, 101, 2–30. doi:10.1016/j.jpba.2014.06.012 · PubMed 25044089
2. Roux S, Zékri E, Rousseau B, Paternostre M, Cintrat JC, Fay N. (2008). Elimination and exchange of trifluoroacetate counter-ion from cationic peptides: a critical evaluation of different approaches. Journal of Peptide Science, 14(3), 354–359. doi:10.1002/psc.951
3. Erckes V, Streuli A, Chamera Rendueles L, Krämer SD, Steuer C. (2025). Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides and Its Influence on Membrane Permeation. Pharmaceuticals, 18(8), 1163. doi:10.3390/ph18081163 · PMC12389442

Research Use Only. Hermetica Research Labs supplies laboratory reagents for in-vitro research. Not for human or veterinary use. Buyers must be 21 or older.