A certificate of analysis is only as useful as the method behind it. Here is how to read a peptide COA, what HPLC and mass-spec confirmation mean, 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, as measured by high-performance liquid chromatography (HPLC). A figure of 99.42% means the instrument resolved that fraction as the intended peptide. It is a measurement of one specific lot, not a brand-wide promise.
Mass-spec confirmation answers a different question
HPLC tells you how much of the sample is one thing; mass spectrometry tells you whether that thing is the right thing. A COA that reports both HPLC purity and mass-spec confirmation is answering both the purity and the identity question. One without the other leaves a gap.
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.