TeamDoes a 99% or 100% purity COA prove the vial contains the labeled amount?

No. A 99% or 100% purity result answers a narrower question: of the peptide-related material detected by that HPLC method, how much appeared as the main peak? It does not automatically prove the compound is the peptide named on the label, that the vial contains the advertised milligrams, or that the batch passed sterility and endotoxin testing.\n\nA useful pre-buy proof ladder is:\n\n1. Match the lot number on the COA to the lot being sold.\n2. Confirm the report names an independent lab and provides a verifiable report ID.\n3. Look for identity testing, commonly mass spectrometry, not HPLC purity alone.\n4. Look for quantitative net-content or fill testing. This is the result that checks whether a vial labeled 10 mg is actually near 10 mg.\n5. Check sterility and endotoxin results where the vendor provides them.\n6. Compare price per tested mg, not simply price per labeled vial.\n\nThat last point can change the value calculation. A vial labeled 10 mg looks like .00 per mg. If quantitative testing showed only 8 mg, the effective cost is .75 per measured mg. Purity could still read 99% because purity and fill are different measurements.\n\nA displayed 100.00% result also does not mean zero impurities exist anywhere. It generally means no other reportable peak appeared above the methods detection and integration thresholds.\n\nPeptidePub breaks down each proof layer in the [COA buyer guide](https://www.peptidepub.com/blog/how-to-read-peptide-coa-before-you-buy). Once the documentation checks out, compare sellers on the [vendor page](https://www.peptidepub.com/vendors). The best deal is the lowest price backed by lot-matched identity, purity, and measured fill.