Updated 2026-09 · 5 min read
A Certificate of Analysis is the laboratory's record of what it measured in a specific lot. It is the most useful document a supplier can publish and the most commonly misread, because its four core figures answer four different questions and two of them are routinely confused.
Purity is not identity
The purity figure — reported by HPLC — says how much of the peptide present is the intended sequence rather than a truncated fragment or a synthesis by-product. It says nothing about which peptide it is, and nothing about how much is in the vial. A sample can be 99% pure and be the wrong compound, or the right one at half the stated mass.
Identity is the separate answer. Confirmed by mass spectrometry, it establishes that the molecule matches the reference at the molecular level. Purity grades the sample; identity names it. A COA worth trusting reports both.
Net content belongs to one lot
Net peptide content is what the laboratory actually weighed, stated against the labelled amount. It is the only figure that speaks to how much material a vial holds, and it is measured per lot — a result on one batch is not a promise about the next.
What a complete COA carries
- The compound and the lot the certificate describes
- Purity by HPLC, with the method stated
- Identity confirmation, typically by LC-MS
- Net peptide content against the label claim
- The laboratory, the test date, and an accession or report number
Where a certificate omits a figure, a careful supplier leaves it blank rather than inferring it. A blank is information: it says the test was not run or the result was not reported, which is more useful than a number nobody measured.
In the catalog
This material is synthesized from publicly available preclinical literature and industry documentation for qualified laboratory researchers. It is not medical, veterinary, therapeutic, or diagnostic advice. All compounds are supplied and discussed solely for in-vitro laboratory research and are not for human or animal use.