How to read a certificate of analysis (COA)

What a COA is

A certificate of analysis documents the test results for one specific sample of material. It is issued by the testing laboratory and always refers to the material that was submitted, never to a product in general. A COA without that reference is worthless, because it cannot be tied to any material that physically exists. The document records what was measured, with which method and on which date. It describes the sample that reached the laboratory, not the product name printed at the top of the page.

The essential details

• Product and sequence: name of the peptide, where applicable sequence or molecular formula.
• Report reference: a report number or date that ties the document to the material tested.
• Test method: HPLC is standard for purity, mass spectrometry for identity.
• Result: purity in percent (area percent of the main peak), measured mass compared with the theoretical mass.
• Test date and laboratory: who tested, and when.
• Sample description: what was submitted, in which quantity and in which form.

Putting purity into context

A figure such as “99.2 %” describes the share of the main peak in the total area of the chromatogram at the wavelength used. It says nothing about water content, counter-ions or net peptide content. Two COAs are therefore only comparable if method and wavelength are the same: one vial measured at 214 nm and at 280 nm can yield two different numbers, because the detector responds to different parts of the molecule. More on this in the guide Purity of research peptides.

Identity: mass, not assumption

Mass spectrometry provides the measured molecular mass. If it matches the theoretical value of the sequence – within the measurement tolerance – identity is confirmed. A high HPLC value alone is not enough: a pure but wrong peptide would also show a clean peak. The two results answer different questions and are read together, never one instead of the other.

What the chromatogram adds

Where the trace is attached, it shows more than the single number derived from it. Worth looking at: whether the baseline is flat and returns after the main peak, whether the run was long enough for late-eluting components to appear, whether small peaks were integrated or fell below the integration threshold, and how far the main peak is separated from its neighbours. A percentage quoted without the underlying trace cannot be checked, only believed.

How to recognise a reliable certificate

1. The product named on the COA matches the label on the vial.
2. The laboratory is named and independent of the seller.
3. Method, instrument or conditions are stated.
4. The chromatogram or spectrum is attached or available on request.
5. The test date is consistent with the material supplied.
6. The file has not been reduced to the headline figure alone.

Typical mistakes

• Comparing two percentages that were produced with different methods or at different wavelengths.
• Treating a purity figure as a statement about the amount of peptide in the vial.
• Carrying an older report over to material that was delivered later.
• Accepting a document in which laboratory, date or method is missing.

Where to find the COAs at GPeptides

All available certificates are in the lab section, sorted by product; listings in the shop overview link to the most recent report for that product where one has been published. Testing is commissioned regularly from an external, independent laboratory, and every report names the material it belongs to, so it can be held against the label. If a certificate is missing, the product is marked as “pending” – we add it as soon as the laboratory delivers. The steps from goods receipt to publication are set out in the quality-control guide.

The methods behind these numbers – separation, detection and mass determination – are described in the guide HPLC and mass spectrometry.