Reading a Peptide Certificate of Analysis in Two Minutes
A five-field checklist for qualifying a lot from its COA — lot match, HPLC purity and method, mass-spec identity, and water/counterion content.
Check the lot number first
The lot or batch number on the certificate must match the number printed on the vial in your hand. If it does not, the document describes different material and cannot be used to qualify your vial, regardless of how good the numbers look.
A usable certificate also names the independent laboratory that performed the analysis and carries a date. Third-party testing matters because the analyzing lab has no commercial interest in the result.
Purity, then method
Purity is reported from reverse-phase HPLC as the main peak's area divided by total peak area, typically with UV detection at 214 nm. Read the number, then read the method conditions beneath it: column chemistry, gradient, flow rate, and run time. A short, steep gradient can co-elute impurities with the target and inflate the apparent figure, so purity values are only comparable when methods are comparable.
Identity and residual content
Mass spectrometry establishes identity by comparing the calculated molecular weight from the sequence against the observed mass. Expect agreement within the instrument's stated tolerance, and remember that multiply charged ions appear at a fraction of the neutral mass — an m/z near half the expected value is usually a doubly charged ion, not a different compound.
Finally, check water content and counterion content. Both contribute to the weighed mass of a lyophilized vial, so a lot with high residual water contains less peptide than the label mass implies. Where a net peptide assay is reported, that is the figure to use for precise molar calculations.
References
These products are sold strictly for in-vitro laboratory research and are not intended for human consumption, diagnosis, treatment, or any therapeutic use. Purchaser must be 18 years of age or older and confirms they are a qualified researcher.