What to actually check on a peptide COA

A certificate of analysis shows up in almost every conversation about buying research peptides, and almost nobody explains what it is actually supposed to prove. Here is what separates a real one from a template with numbers filled in. What a COA is A certificate of analysis is a lab's written record that a specific batch of material was tested, and what the tests found. Two tests matter most for a peptide: HPLC, which measures purity as a percentage, and mass spectrometry, which confirms the molecule is actually the one it claims to be rather than something the wrong molecular weight. Purity without identity confirmation tells you the batch is 99% pure something. Identity without purity tells you it is the right molecule mixed with an unknown amount of everything else. You want both, from the same batch, on the same document. The word that matters most: batch-specific A COA that is not tied to a specific batch or lot number is not a certificate of that product, it is a certificate of a product like it, once, maybe. Peptide synthesis varies batch to batch. A supplier who ran one real test eighteen months ago and now attaches that same PDF to every order is not lying about the test happening. They are lying about what it tells you. The batch number on the COA has to match the batch number on what actually ships, and if a supplier cannot show you that connection, the document is decorative. Who ran the test Third-party means a lab with no financial stake in the result, testing on the supplier's behalf but not owned by or dependent on the supplier. An in-house test is not worthless, but it is not independent, and a COA that does not name the testing lab at all is the easiest of these checks to fail. A real lab name is checkable. Search it. Real testing labs have a web presence, a physical address, and other clients who reference them. Reading the purity number in context 99% purity sounds like a pass or fail number, but the real question is what fills the other 1%: residual solvents from synthesis, unreacted starting material, or a related peptide sequence that is close enough to pass a casual glance but is not the compound on the label. A thorough COA breaks out related substances rather than reporting a single purity figure. A number with nothing behind it is a claim, not a measurement. What we actually check When a supplier applies to be listed on A Peptide Store, we read every COA against the product it is supposed to cover: does the batch number match, is the testing lab real and identifiable, does the report show both purity and identity testing, and does the purity figure hold up against its own related-substances breakdown. We do not run our own tests. We are not a lab, and pretending otherwise would be exactly the kind of claim this whole site refuses to make. What we check, and what we do not, is stated on every listing, because a verification badge that does not say what it verifies is just decoration with a different shape. If you already have a COA in hand You do not need to be a chemist to catch the most common problems: no batch number, no named testing lab, a purity figure with no supporting data, or a document that reads like it was written for a different product entirely and never updated. Those four checks alone rule out a meaningful share of what circulates. The rest takes knowing what to look for, which is the entire reason this page exists.