How to read a peptide certificate of analysis

A certificate of analysis is the only document that connects a vial in your freezer to a measurement someone actually made. It is also the easiest document in this industry to fake, so it is worth knowing what a real one says.

The three questions a COA has to answer

A COA that is worth anything answers identity, purity and quantity. Everything else is context.

• Identity — is this molecule what the label says? Mass spectrometry answers this. Look for an observed mass that matches the theoretical mass of the sequence, usually within a fraction of a dalton.
• Purity — how much of the material is the target molecule? This comes from HPLC, reported as area percent at a stated wavelength. A number with no chromatogram behind it is a claim, not a result.
• Quantity — how much is in the vial? Net peptide content, not gross fill weight. Lyophilised powder carries counter-ions and residual water.

What a purity figure actually means

"99% purity by HPLC" means that 99% of the area under the curve, at one wavelength, belonged to one peak. It does not mean the vial is 99% peptide by mass, and it says nothing about what the other 1% is.

This is why the chromatogram matters more than the headline. A clean baseline with one sharp peak is a different material from a 99% figure sitting on top of a noisy baseline with three shoulders.

Red flags

1. No batch number. A COA that cannot be tied to a specific lot describes nothing you can verify.
2. No test date. Peptides degrade. A two-year-old result on freshly shipped material is not evidence about that material.
3. No lab name, or a lab that does not exist. Third-party means a lab you can look up and contact.
4. Identical documents across products. Real chromatograms differ. Reused images mean reused claims.
5. Purity quoted to two decimal places. HPLC area percent is not that precise. It reads as confidence, not rigour.

How we publish ours

Every batch we sell has its certificate on the product page and in the COA library, with the batch number, the test date and the measured purity. If a batch has not been tested, it is not listed. That is the whole policy.

Research use only. Nothing on this site is intended for human or veterinary use.