A COA is only as trustworthy as the lab that issued it. Learn what each line of a peptide certificate of analysis actually proves — and the red flags of a fabricated document.
Every legitimate research peptide ships with a certificate of analysis. Every counterfeit one does too. The difference is not whether a PDF exists — it is whether the data inside it is specific, internally consistent, and traceable to a real analytical run. This guide walks through a COA line by line.
The five things a real COA must show
- Batch or lot number — unique to a single synthesis run, and matching the label on your vial.
- HPLC purity — the percentage of the sample area under the main peak. Research-grade material should read ≥98%.
- Mass spectrometry result — the observed molecular weight, which should match the theoretical mass of the peptide within instrument tolerance (typically ±0.5–1 Da on a well-calibrated instrument).
- Appearance and solubility — qualitative but expected; lyophilized peptides should be described as a white to off-white powder or cake.
- Test date and analyst or laboratory identification — a COA without a date or issuing lab is decorative, not evidentiary.
What HPLC purity actually means
HPLC separates the sample by hydrophobicity and reports purity as the main peak's share of total absorbance area. A 99.2% purity figure means roughly 0.8% of UV-absorbing material is something else — deletion sequences, truncated fragments, or residual protecting groups. What HPLC does not tell you is whether the main peak is the right peptide. A vial of the wrong compound can still test at 99% purity. That is why the mass-spec line matters.
Mass spectrometry: the identity check
Mass spec confirms the peptide is what the label claims. The observed mass should match the calculated monoisotopic or average mass of the target sequence. For acylated peptides like semaglutide or tirzepatide, this is the critical line — it proves the fatty-acid side chain is present and correctly attached.
Red flags of a fabricated COA
- A generic COA with no batch number, or the same document reused across every product a supplier sells
- Purity of exactly 99.00% or '100%' — real chromatograms almost never produce round numbers
- No chromatogram image included when the supplier claims in-house testing
- Test dates that predate the synthesis date of the batch
- Missing mass-spec data on a peptide where identity verification is trivial to perform
- A COA that lists purity but no method (column, gradient, detection wavelength) for how it was measured
The traceability test
The simplest verification step: ask the supplier for the COA of the exact batch in stock before ordering, and confirm the lot number on the vial matches the document when it arrives. Suppliers who manufacture or directly qualify their material can answer this in one email. Resellers three layers removed from the synthesis often cannot.
