Does HPLC purity prove the vial actually contains the peptide I ordered?

No. HPLC measures purity, not identity. It separates a sample by how compounds move through the column (retention time) and reports the main peak as a percentage of everything else. A clean 99% peak only tells you one compound dominates. It does not prove that compound is the peptide on the label. A different molecule with similar properties can co-elute or show a believable retention time. Identity comes from mass spectrometry. MS measures molecular weight, and tandem MS reads the sequence, so it can catch a wrong peptide, a single amino acid substitution, or incomplete synthesis that HPLC misses. As Creative Peptides puts it, purity is "how much else" and identity is "what." Two separate questions. So look for both on a certificate of analysis: an HPLC purity number and an MS identity confirmation. Independent labs like Janoshik run both and assign a unique key you can check at their verification portal, which also confirms the report itself isn't forged. This is research-use information about lab testing, not medical or usage advice. These compounds are not approved for human consumption.