How to Read a Certificate of Analysis (COA)
A COA is the clearest proof that a vial matches its label. Here is how to read each section — HPLC purity, mass-spec identity, net peptide content, and batch traceability.
What a COA Is
A Certificate of Analysis is the document that records the analytical testing performed on a specific batch of a research peptide. It is the difference between a vendor claiming purity and a vendor proving it. A complete COA identifies the compound, the batch or lot number, the date of analysis, the testing laboratory, and the results of the analytical methods used — typically HPLC and mass spectrometry. Reviewing the COA for the exact batch you received is the only way to know what is actually in the vial.
HPLC Purity
The High-Performance Liquid Chromatography (HPLC) section reports purity as a percentage — the proportion of the detected material that is the target peptide. A research-grade standard is generally ≥98-99%. The accompanying chromatogram should show one dominant peak for the target compound, with minimal secondary peaks. Purity tells you how much of the sample is the intended peptide, but on its own it does not confirm the peptide's identity.
Mass Spectrometry Identity
The mass spectrometry (MS) section confirms identity by measuring the peptide's molecular weight and comparing it to the theoretical value calculated from its amino-acid sequence. A match within roughly ±1 Dalton confirms the molecule is structurally what it claims to be. This catches errors that purity testing alone cannot — a sample can be highly pure yet be the wrong compound. Purity (HPLC) and identity (MS) together are what make a COA meaningful.
Net Peptide Content & Traceability
Look for net peptide content, which accounts for salts, residual moisture, and counter-ions — the actual peptide mass can be lower than the gross fill weight. Finally, confirm the batch/lot number on the COA matches the number on your vial, and note the testing lab and date. Where a third-party lab is named, its report can often be verified directly with that lab, adding an independent layer of confidence.
For laboratory and research use only. This guide describes general handling and analytical practice for research reagents and is not medical advice or dosing guidance for human or veterinary use.