How to read a certificate of analysis (COA)

A certificate of analysis (COA, Certificate of Analysis) is a document that links a specific batch of a product to analytical results. In the world of peptides it is often the only evidence the buyer receives before purchase — so it is important to know what to look for in it and what to disregard.

This guide is practical. It does not promise that you will discover every flaw with it, but it helps you separate a serious document from a marketing sheet.

What is a COA?

A COA is a document issued by the manufacturer or an analytical laboratory. It contains information on:

• the identity of the product (name, catalogue number);
• the batch number;
• analytical methods;
• results;
• the date of manufacture or analysis;
• any specifications and limits.

The key word is batch. A product with the same catalogue number may be produced in several batches, and each may have its own analytical results.

What must a credible COA contain?

1. Product identification

• the peptide name and, where applicable, the sequence;
• the catalogue number;
• the pack size;
• the form (lyophilized powder, solution);
• the manufacturer or supplier.

2. Batch number and dates

• a batch/lot number matching the label on the vial;
• the date of manufacture;
• the date of analysis;
• the expiry date.

Without a matching batch number, the COA proves nothing about your vial.

3. Analytical methods

• HPLC for purity, stating the column, mobile phase and wavelength;
• mass spectrometry (MS) for identity, stating the ionisation mode;
• where required, water content (Karl Fischer), salt content or endotoxins.

The method matters because “99 %” without context is not a measurable claim.

4. Results and specifications

It is good if specifications (e.g. ≥ 98 %) and measured values are stated. You can then see whether the result is close to the limit or comfortably within it.

5. Laboratory and signature

• the name of the laboratory;
• the address or website;
• the name of the responsible person and a signature;
• any accreditation (e.g. ISO/IEC 17025).

Accreditation is not an absolute guarantee, but it means that the laboratory operates according to defined procedures.

What does “purity 99 %” mean?

In HPLC, purity is often calculated as the percentage of the main peak area relative to the total area of all peaks at a given wavelength (often 214 or 220 nm for peptides).

This means:

• impurities that do not absorb at that wavelength are not included;
• water and salt content are not part of this number;
• isomers or peptides with the same mass may be hidden;
• the separation method must be adequate for the peaks to be resolved at all.

Therefore 99 % by HPLC is a good sign, but not a complete guarantee.

What does mass spectrometry show?

MS confirms the molecular mass and often the fragmentation pattern. This helps establish whether the molecule really is the one you expect. It is especially important for:

• fragments with similar names;
• modified peptides (acetylation, amidation);
• substitutions with another analogue.

If the COA states only “MS: conforms”, without mass and conditions, that is weak evidence. It is better to see the measured mass and the expected mass.

Red flags

Watch for the following signs:

• A generic COA without a batch number.
• No laboratory name, or an invented logo.
• Only a purity percentage, without a chromatogram.
• A completely identical COA for different products.
• Dates that do not match (e.g. analysis before manufacture).
• A low-resolution photograph of the chromatogram where the integration cannot be seen.
• Claims of 100 % purity — realistically rare and suspicious.
• Lack of storage information and expiry date.

Read more about recognising counterfeits in the thematic article.

What to do if no COA is available?

Ask the supplier for:

1. The COA of the specific batch you will receive.
2. The chromatogram and HPLC conditions.
3. The measured mass by MS.
4. Information on water and salt content.
5. The option of independent analysis of the sample.

If the answers are not clear, that is information in itself.

Example of a good COA summary

A good document can be verified at first glance. It must contain the following blocks:

If any of these blocks is missing, the document is not necessarily forged — but it is incomplete. An incomplete COA is a weaker basis for a decision.

Independent analysis

The strongest form of verification is to send a sample from the purchased batch to an independent laboratory. This is more expensive and slower, but it removes the basic weakness of a COA: the document may describe something other than what is in the vial.

For research laboratories this is often a standard part of procurement, not a luxury.

Conclusion

A COA is a useful document if it is specific, traceable and methodologically honest. Without a batch number, method and laboratory, it is merely decoration. With peptides, where quality is crucial to results, take the time to read the small print.

See the peptide catalogue or read how analysis by HPLC and MS works.