Peptides - Handling & quality
Purity, HPLC and COAs: what the numbers mean
How to read a certificate of analysis: what HPLC measures, what a purity percentage does and does not tell you, and where the gaps are.
A certificate of analysis, or COA, is the document meant to tell you what is actually in a vial. Learning to read one - and to see its limits - is one of the most practical skills in this field.
What HPLC measures
Most purity figures come from a technique called HPLC (high-performance liquid chromatography). In simple terms, it separates the contents of a sample into its components and measures how much of each is present. A result of "99% purity" means that, by this method, 99% of what was detected was the target compound and 1% was other material.
What a purity number does not tell you
- Identity: purity says the sample is mostly one thing, not that the one thing is the compound on the label. Identity needs a separate test, such as mass spectrometry.
- Quantity: a sample can be pure and still contain more or less than a stated amount.
- Contaminants the method misses: not everything shows up on a given HPLC run.
- What happened afterwards: a COA describes the batch when it was tested, not how it was stored since.
A good COA is a genuine quality signal - but only if it is real, specific to a named batch, and from an independent lab. A vague or generic certificate tells you very little, however reassuring it looks. Learning to read the document, rather than being reassured by its existence, is the whole point.
Educational content only. Not medical advice.
Further reading
Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.
