Quality & Testing
Peptide Purity and the Certificate of Analysis: A Researcher's Guide
HPLC, mass spectrometry, and what an honest CoA actually looks like — plus how to read one without being misled.
A Certificate of Analysis (CoA) is the single most important quality artifact in research peptide procurement. It is also, unfortunately, the most commonly misrepresented. Knowing what a credible CoA contains — and what its absences imply — is a baseline skill for any laboratory sourcing reference compounds.
What HPLC tells you
Reversed-phase high-performance liquid chromatography (RP-HPLC) separates a peptide from synthesis-related impurities (truncated sequences, deletion products, oxidation variants). The 'purity' value on a CoA is conventionally the area-under-curve of the target peak as a percentage of total UV-absorbing material at 214 nm (peptide-bond absorption).
What mass spectrometry tells you
Mass spec — typically ESI-MS or MALDI-TOF — confirms peptide identity by molecular mass. HPLC alone shows you something is pure; MS confirms that it is the molecule you intended. A complete CoA includes both.
What a credible CoA contains
- Lot or batch number traceable to a specific synthesis run
- HPLC chromatogram with method parameters (column, gradient, detection wavelength)
- Mass spec spectrum with observed vs theoretical mass
- Net peptide content (corrected for counter-ion and residual water)
- Date of analysis and signature of the analytical chemist
Red flags
Beware CoAs without lot numbers, without chromatograms, with identical-looking chromatograms across different products, or with purity values quoted without analytical conditions. A CoA that cannot be tied to a specific synthesis batch is, in practice, marketing copy.
Third-party verification
An in-house CoA is necessary but not sufficient. Independent third-party verification — from an unaffiliated analytical laboratory — eliminates the supplier's conflict of interest. The cost (typically €30–€80 per sample) is trivial compared to the risk of building a multi-month study on misidentified material.
For research use only. All products are sold strictly as analytical reference material.
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