A CoA is a supplier's own report on a specific batch. It is not independent verification, and a PDF is trivially edited — so the first question is always whether the document names a batch you can match to the vial in front of you, and an analytical lab you can look up.
Purity by HPLC
Reverse-phase HPLC separates the sample over time and reports each component as a percentage of total peak area, usually at 214 or 220 nm where the peptide bond absorbs. A figure like 99.1% means the main peak is 99.1% of what the detector saw — not that the vial is 99.1% peptide by mass.
That distinction matters. Water and counterion do not show up as impurity peaks, so a high HPLC purity is entirely compatible with a vial whose net peptide content is meaningfully below the labelled mass. A trustworthy CoA shows the chromatogram, not just the number.
Identity by mass spectrometry
Mass spec confirms the molecule is the one claimed, by matching observed mass against the theoretical mass of the sequence. Purity without identity is close to meaningless — it says the vial contains one thing, not that it contains the right thing. Check the observed mass against the monograph.
The things most often missing
- Net peptide content — the fraction of the labelled mass that is peptide rather than counterion and water.
- Water content, typically by Karl Fischer titration.
- Counterion identity and amount (see the acetate versus TFA guide).
- Bacterial endotoxin, which matters for any material used in cell culture.
- The date of analysis, and whether it refers to this batch or an earlier one.
A CoA describes a batch, not a compound. It says nothing about whether a compound is safe or effective, and inclusion of a supplier anywhere on this site is never an endorsement.