Why the COA is the product
In research supply, the certificate of analysis is not paperwork attached to the product: in a real sense it is the product. A white powder in a vial is unverifiable by inspection. The COA is the independent evidence that the vial contains what the label claims, at the purity claimed, without contaminants that would confound results.
The sections that matter
1. Identity
Usually established by mass spectrometry (MS). The measured molecular weight should match the theoretical mass of the peptide sequence within instrument tolerance. If the COA doesn’t state a theoretical vs. observed mass, ask why.
2. Purity
Typically HPLC (high-performance liquid chromatography), reported as a percentage: the area of the main peak relative to all peaks. Research-grade peptides commonly specify ≥98%. Look for the chromatogram itself, not just the number: a clean single peak tells you more than a summary figure.
3. Quantity
Net peptide content per vial. Note that lyophilized mass includes counter-ions and residual moisture; a “5 mg” vial’s actual peptide content depends on how the vendor fills (by gross weight or by net peptide assay). The COA should say which.
4. The lab itself
An in-house COA is a claim; a third-party COA is evidence. Check that the testing laboratory is named, independent of the vendor, and that the document carries a date and a lot number matching the vial in hand.
Red flags
- No lot number, or a lot number that doesn’t match the product label
- A purity percentage with no chromatogram
- Identity “confirmed” without mass spec data
- An undated certificate, or one recycled across multiple lots
- No named laboratory
Matching a COA to your vial
The chain is: vial label → lot number → COA for that lot → named third-party lab. If any link is missing, the certificate certifies nothing. When a vendor publishes a COA library, verify your specific lot appears in it rather than relying on a representative example.