Quality · 6 min
How to Read a Peptide Certificate of Analysis
What a COA documents
A Certificate of Analysis is the quality unit's record that a specific lot meets defined specifications. It is not a marketing document. It is dated, lot-specific, and signed.
Identity
Identity confirmation typically uses mass spectrometry. The observed mass should match the calculated mass within instrument tolerance. CAS number, molecular formula, and amino acid sequence anchor the identity claim.
Purity
Purity is most commonly reported by reverse-phase HPLC at 220 nm, the wavelength at which peptide bonds absorb. The principal peak should integrate to ≥99.0% of total peak area for reference-grade material. The method should be stated.
Water and counter-ion content
Karl Fischer titration reports water content. Acetate is the most common counter-ion from synthesis; it is reported as a percentage and affects mass-balance calculations when dissolving the lyophilized powder.
Endotoxin and bioburden
For research use these are reported in EU/mg and CFU/g respectively. They are quality indicators of synthesis and handling.
Storage and retest dates
A COA documents the storage condition under which the specification holds and the retest date — the point at which the material should be re-verified against specification rather than discarded outright.