Peptide COA library and reading guide

What a certificate of analysis is

A COA is a test report tied to one production lot. It is not a general product sheet and it is not a promise about every vial ever made. When a lot is manufactured, a sample from that lot is analysed and the results are recorded against the lot number. If the lot number on your vial does not match the lot number on the certificate, the certificate is not describing your material.

A useful COA answers four questions: what was tested, which lot it came from, how it was tested, and who tested it and when. Anything missing from that list reduces what the document can tell you.

The fields on a COA, in order

• Compound name and fill size — what the lot is labelled as, and the nominal amount per vial (for example, 10 mg).
• Lot (batch) number — the key that links the paper to the physical vial.
• Test date — when the analysis was run. Older dates are normal for stable lyophilised material, but the test date should come after the manufacture date.
• Laboratory — the lab that ran the analysis.
• Purity by HPLC — a percentage, ideally with the detection wavelength stated.
• Identity by MS — the observed mass compared with the expected (theoretical) mass.
• Appearance — usually "white to off-white lyophilised powder".
• Chromatogram and spectrum images — the raw traces behind the numbers.

What HPLC shows

High-performance liquid chromatography (HPLC) separates the components of a sample as it passes through a column. A detector, usually UV at a stated wavelength such as 214 or 220 nm, records a peak for each component. The purity figure is the area of the main peak divided by the total area of all detected peaks — "area percent".

What that means in practice:

• It is relative, not absolute. Area percent tells you how much of what the detector saw belongs to the main peak. It does not tell you the total peptide mass in the vial; water, counter-ions and salts do not appear as peaks. That separate figure is net peptide content (see HPLC area percent vs net peptide content).
• The wavelength matters. Different wavelengths can give slightly different numbers. A purity value with no wavelength is harder to compare.
• Look at the chromatogram. A clean report shows one dominant, sharp peak and small side peaks. A stated purity that does not match the picture is a red flag.

What MS shows

Mass spectrometry (MS) measures the mass of the molecules in the sample. For a peptide, the lab compares the observed mass with the theoretical mass calculated from the sequence. A close match confirms identity: that the main component is the molecule named on the label.

HPLC and MS answer different questions. HPLC says how clean the sample is; MS says what the main component is. A high HPLC purity with no MS identity tells you the sample is clean, but not that it is the right compound. You want both, on the same lot.

When reading the MS section, check that:

• the expected mass is stated, and the observed mass is close to it;
• multiply-charged ions, if shown, are consistent with the same molecule;
• the spectrum belongs to the same lot number as the HPLC result.

How to match your vial to its COA

1. Read the lot number on the vial label (and on the box, if present). Note it exactly, including letters and dashes.
2. Find that lot in the library above. Search by lot, or filter by compound and fill size.
3. Open the PDF and compare the lot number, compound name and fill size with your label. All three should match.
4. Check that the date and laboratory fields are present.
5. If you cannot find your lot, contact us with the lot number and order number. Published Lab COA PDFs are listed in the COA library.

A COA for the same compound but a different lot is not evidence about your vial. That is the whole point of lot matching.

Common red flags on any supplier's COA

• No lot number, or a lot number that never changes across orders.
• A purity figure with no chromatogram, no wavelength and no lab name.
• Identity claimed without an MS result or expected mass.
• A test date before the stated manufacture date.
• Identical documents reused across different compounds or fill sizes.
• Images cropped so that the lab name or lot cannot be read.

For a broader checklist, see how to verify a peptide supplier.

What a COA does not tell you

A COA describes the composition of a tested sample. It does not describe suitability for any use outside the laboratory, and it is not a statement about biological activity or outcomes. Storage and handling after delivery also matter: lyophilised material is generally kept cold, dry and away from light, following the documented storage conditions.

Further reading

• HPLC and MS explained
• Why a lot COA matters more than a purity percentage
• HPLC area percent vs net peptide content