How to read a research peptide COA (and how to spot a fake one)

A Certificate of Analysis is the only evidence you have, before the vial is opened, that the material in it is what the label says. It is also the document most often faked, borrowed or quietly recycled in the UK research peptide market. This note explains what a genuine COA contains, how to read the parts that matter, and the four checks that catch almost every problem COA we have seen.

What a Certificate of Analysis is supposed to prove

A COA is a report issued by an analytical laboratory describing the tests run on a specific batch of material and the results. For a research peptide the questions it should answer are simple:

• Identity: is the compound the one claimed? Usually confirmed by mass spectrometry, where the observed molecular weight matches the theoretical value for the sequence.
• Purity: what fraction of the peptide content is the target sequence, versus related substances (deletion sequences, oxidation products, truncated chains)? Usually measured by reverse-phase HPLC.
• Net content: how much material is actually in the vial, and how much of that is water or counter-ion rather than peptide.
• Batch: which specific lot these results describe.

Anything that does not answer those questions for the batch you are holding is marketing, not analysis.

The anatomy of a genuine peptide COA

1. Header: issuing lab, batch number, dates

The top of the document should name the laboratory that ran the tests, with an address and contact details, and state the batch or lot number. That batch number must match the number printed on the vial label. It should also show a test date. If the supplier's own name is the only name on the document and no independent lab is identified, treat the results as the supplier's claim rather than a third-party finding.

2. HPLC purity: the chromatogram, not just the number

The purity figure everyone quotes (98%, 99%, 99.5%) is derived from an HPLC chromatogram: a trace of detector response against retention time. The main peak is the target peptide; anything else is an impurity. A genuine COA shows the trace, the integration table (peak retention times and area percentages), and the method conditions: column, gradient, flow rate, detection wavelength (220 nm is standard for peptide bonds).

A bare "Purity: 99.2%" with no chromatogram is the single most common feature of a low-quality COA. Without the trace you cannot see whether the main peak has a shoulder (a co-eluting related substance), whether the baseline was drawn sensibly, or whether the integration excluded early or late peaks. Ask for the trace. A supplier that has it will send it.

3. Mass spectrometry: identity

The MS section should state the theoretical molecular weight for the sequence and the observed mass, typically by ESI-MS. For research peptides the observed value should sit within about 1 Da of theoretical (multiply-charged species are reported deconvoluted). A COA that omits MS entirely has confirmed purity of something without confirming what that something is.

4. Water content and counter-ion (optional extras)

Lyophilised peptides retain water and carry a counter-ion (usually trifluoroacetate or acetate) from purification. Some COAs additionally report water content or net peptide content; most, including ours, report HPLC purity and leave net-content interpretation to the researcher. The absence of a water-content figure is not a sign of a fake. The absence of the chromatogram or the MS result is.

The four checks that catch most fake or borrowed COAs

1. Batch number mismatch. The number on the COA is not the number on the vial. This is the commonest failure and usually means the supplier is sending one "representative" COA with every order, regardless of lot.
2. Test date more than six months old. Suggests the lab tested a precursor lot, or an early batch, and the document has been reused for later production runs.
3. No chromatogram, only a purity number. See above. If the trace is not on the document and the supplier will not send it, assume the number is unverifiable.
4. Issuing lab not identified, or details scrubbed. A genuine analytical lab puts its name on its work. Redacted addresses, missing contact details, or a logo you cannot trace to a real laboratory are all tells. Some sellers overlay their own branding on a lab template; the lab's name should still be legible.

Two further tells worth knowing: identical purity values to two decimal places across many different compounds from the same seller (real batches vary), and image artefacts around the numbers on a scanned COA (numbers pasted over an original).

What an Alphex COA contains

Every batch we sell is tested before it is listed. The COA for that batch includes:

• Batch number matching the vial label
• Test date as reported by the laboratory
• Full RP-HPLC chromatogram at 220 nm with integration table and method conditions; acceptance threshold 99+% purity
• The issuing third-party laboratory's name and address

The COA for every batch is published in the COA library, chromatogram included, so you can read it before you order. After delivery, type the batch code printed on your vial label into the library to pull up that exact certificate.

Applying this to any supplier

Use these questions on every vendor, including us. Ask for the COA of the batch that is actually in stock, not a representative document. Check the batch number against what arrives. Look for the trace, the MS result and the lab name. If any of the four checks fails, the purity claim on the product page is not evidence of anything. Our 12-point UK supplier checklist builds on this into a full procurement test.

All Alphex products are supplied for laboratory and in-vitro research only and are not authorised for human or veterinary use.

Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.

Published 22 April 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.

Alphex Research Team

Alphex Limited, UK research peptide supplier

The Alphex research team writes and maintains these notes for UK laboratories buying research peptides. Every batch Alphex lists is verified by reverse-phase HPLC with a batch-matched Certificate of Analysis. Content covers laboratory and in-vitro research only.