A certificate of analysis (COA) is the document that accompanies a batch of research peptide. It is often read as a single verdict — '99% pure' — when in fact it reports two orthogonal measurements, and frequently omits a third.
Two numbers, two questions
Reversed-phase HPLC reports purity: what proportion of the peptide-related material in the sample is the intended sequence, rather than deletion sequences, truncations, oxidised forms or other synthesis by-products. Mass spectrometry reports identity: whether the material present has the expected molecular mass. A COA carrying only one of the two is incomplete. HPLC purity without a mass spectrum quantifies how clean the material is but not what it is; a mass spectrum without HPLC confirms identity but says nothing about purity.
What '99% pure' does and does not mean
The purity figure is a statement about a chromatogram. A peptide reported as 99% pure by HPLC is 99% of the peptide-related material — the number does not account for non-peptide mass. The gap between a purity claim and the reality of a grey-market vial was demonstrated in 2026, when Sky News had unregulated peptide products bought in the UK tested by a UK laboratory; a product labelled 99% pure tested at approximately 10%.
Net peptide content: the number nobody checks
A vial labelled '10 mg' is usually 10 mg of lyophilised powder, not 10 mg of peptide. The powder also contains counterions, residual water and residual solvents. Net peptide content (sometimes simply 'peptide content') expresses the proportion of the powder mass that is actually the target peptide.
Most synthetic peptides purified by reversed-phase HPLC are supplied as trifluoroacetate (TFA) salts, because trifluoroacetic acid is used as a mobile-phase additive during purification. Basic residues (arginine, lysine, histidine) and a free N-terminus carry TFA counterions that contribute to the mass. Theoretical net peptide content can be estimated by dividing the peptide's molecular weight by that weight plus the mass of the required counterions (TFA molecular weight approximately 114); measured content also reflects water and residual solvents. For a TFA-salt peptide, content is frequently in the 70–85% range.
The consequence is that a COA reporting 99% HPLC purity alongside 78% net peptide content is internally consistent. It means the peptide present is very pure, and the powder is 78% peptide. Where a research calculation assumes otherwise, every downstream figure is out by more than a fifth.
What a complete batch record should contain
- A batch or lot number matching the vial supplied
- HPLC purity as a percentage, with the conditions stated — column, gradient and detection wavelength
- Mass spectrometry identity data, observed against theoretical mass
- The salt form (TFA, acetate, hydrochloride or free base) and, where declared, peptide content
- Residual moisture, and endotoxin testing where the research context requires it
- The date of analysis
Independent verification
A manufacturer's own COA is a claim about its own product. Only an accredited independent laboratory testing a received sample constitutes verification. Peptide Data's vendor reviews are built on third-party laboratory testing for that reason.
The UK framing
Under the Human Medicines Regulations 2012, a product sold for human use as a medicine requires a marketing authorisation. Research peptides sold under a 'research use only, not for human consumption' label sit outside that authorisation, which is precisely why batch-level documentation carries the weight it does. A COA is not a licence and it is not a safety guarantee; it is a record of analytical testing on one batch. Nothing here is consumption advice.
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.