Posted by Marcus Chen | Pinned A Certificate of Analysis is the single most important document you'll never read — until now. It's the lab report card for your peptide, and if you're not checking it, you're flying blind. Think of it this way: you wouldn't buy a used car without a Carfax report. A COA is the Carfax for your peptide. It tells you what's actually in that vial, how pure it is, and whether it's going to do what you think it's going to do. What a COA Is A COA is a document provided by the manufacturer or a third-party lab that details the testing results for a specific batch of peptide. Every batch should have one. If you can't get a COA for the specific batch you purchased, that's problem number one. Key Sections to Look At 1. Peptide Identity / Sequence Confirmation This confirms the peptide is actually what the label says it is. Methods used are typically mass spectrometry (MS) or HPLC-MS. You're looking for the molecular weight to match the expected value for that peptide sequence. If the molecular weight is off by more than 1-2 daltons, something's wrong. Either it's the wrong peptide, or there are significant impurities. 2. Purity (HPLC) This is the big number everyone looks at. It's expressed as a percentage, determined by High-Performance Liquid Chromatography. • >98% — Pharmaceutical/research grade. This is what you want. • 95-98% — Acceptable for most research purposes. • <95% — Ask questions. What's the other 5%+? Degradation products? Synthesis byproducts? • <90% — Walk away. A vendor advertising "99% purity" but the COA says 96%? That's not a rounding error. That's dishonesty. 3. Endotoxin Testing (LAL Test) Endotoxins are bacterial toxins that can cause fever, inflammation, and worse. The Limulus Amebocyte Lysate (LAL) test measures these. You want to see: • <5 EU/mg — Standard acceptable level • <1 EU/mg — Even better If there's no endotoxin data on the COA, that's a yellow flag. For injectable peptides especially, this test is non-negotiable.