Yesterday I asked: When you look at a peptide COA, what’s the first thing you check? Now let’s break down some of the important things a Certificate of Analysis can tell you — and what it doesn’t tell you. 1. Identity First question: Is the compound actually what the label says it is? Depending on the testing method, identity may be evaluated using techniques such as mass spectrometry. A purity percentage alone does not necessarily establish identity. 2. Purity HPLC (High-Performance Liquid Chromatography) is commonly used to evaluate peptide purity. You may see results such as 98%, 99%, or 99%+ purity. Remember: purity describes the proportion of detected material represented by the target compound under that analytical method. It does not automatically tell you how many milligrams are in the vial. 3. Quantity / Peptide Content This is different from purity. A vial can test at very high purity and still contain more or less peptide than the amount stated on the label. Look for testing that actually evaluates peptide content or quantity, when available. 4. Sterility & Endotoxin Testing These are separate tests from purity and identity. A standard HPLC purity report does not prove that a sample is sterile or establish its endotoxin level. If those characteristics are being claimed, look for the appropriate separate testing. 5. Lot or Batch Number The COA should be traceable to the specific batch or lot it represents. A beautiful COA isn't very useful if you can't determine whether it corresponds to the actual batch being discussed. 6. Testing Date Check when the sample was analyzed. Testing dates help establish when the reported results were obtained. 7. Testing Laboratory Look at who performed the analysis. Ideally, the laboratory and report should be independently verifiable rather than relying solely on a screenshot supplied by a seller. THE BIG TAKEAWAY Purity ≠ quantity ≠ sterility ≠ identity. They answer different questions and may require different analytical methods.