Article: What does purity % mean on a peptide COA?
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What does purity % mean on a peptide COA?
Purity percentage on a Certificate of Analysis (COA) refers to the proportion of the detected material that matches the expected compound under a specific analytical method, most commonly High-Performance Liquid Chromatography (HPLC).
It does not mean the material is “perfect,” nor does it describe biological performance. It simply indicates how much of the sample matches the expected retention profile compared to detectable impurities under the testing conditions.
A reported purity of 99% means:
- 99% of detectable peaks correspond to the expected compound
- 1% represents minor synthesis byproducts or impurities
Purity must always be interpreted alongside:
- The chromatogram
- The HPLC method used
- The lot number and testing date
A purity number without a chromatogram has little value.