A certificate of analysis is only as useful as the tests behind it. Here is how to read a peptide COA, why purity is only one of six questions, and what to distrust.
Every reputable peptide supplier will hand you a certificate of analysis. Fewer will tell you how to read one — and the differences matter when you are placing a wholesale order.
Purity is a measurement, not a grade
The headline figure on a COA is purity: the proportion of the sample that is the target compound. A figure like 99.42% means testing resolved that fraction as the intended peptide. It is a measurement of one specific lot, not a brand-wide promise.
Purity is only one of six questions
Purity tells you how much of the sample is the target compound. It does not tell you whether the identity is correct, whether the fill quantity matches the label, or whether the vial is sterile, free of endotoxins, and clear of heavy metals. A complete release test answers all six — purity, identity, quantity, sterility, endotoxins, and heavy metals. A COA that reports purity alone leaves five questions open.
Tie the certificate to a lot
A certificate that is not bound to a lot number is decoration. The value of a COA is that you can match the figure on the vial to the record on file, years later. That is why every lot we sell carries its lot code on the label and in a searchable library.