A certificate of analysis, or COA, is the document that turns a claim into evidence. It reports what testing found about a specific batch of material, and knowing how to read it is a core research skill.
Start with the identification section. This states the product name, the batch or lot number, and often the sequence or molecular formula. The lot number matters more than it looks: a COA is tied to one specific batch, so it should match the batch you actually received.
Next, the purity result, usually reported from HPLC as a percentage. This tells you what proportion of the sample is the intended compound versus impurities. A high figure from a clean chromatogram indicates a well-made product; the accompanying chromatogram image, if included, lets you see whether that number comes from one dominant peak or a messier profile.
Then the identity confirmation, typically from mass spectrometry. This reports the measured molecular mass against the expected value. A close match confirms the molecule is what it claims to be. As covered elsewhere, purity and identity are separate questions, and a complete COA addresses both.
Additional fields may include appearance, water or solvent content, and the analytical methods used. The methods line is worth checking — it tells you how the conclusions were reached.
Read as a whole, a good COA lets you trace a specific vial back to specific measurements. The habit to build is simple: match the lot number, confirm both purity and identity are present, and treat any missing section as a question rather than an assumption.
