What Peptide Purity Actually Means

When a COA states a purity of 99%, it describes the outcome of an analytical separation: 99% of the signal in the chromatogram corresponds to the target peptide. It is an empirical result, not a grade a supplier assigns themselves.

Purity is method-dependent. A result is only meaningful alongside the method used to produce it — which is why reputable documentation always names the technique.

Even in a high-purity preparation, the non-target fraction exists. It typically consists of closely related synthesis byproducts — truncated or deletion sequences — plus trace water and counter-ions from the purification process.

This is distinct from net peptide content, which accounts for the total mass of the vial. A vial can be 99% pure by HPLC while some of its weight is water and salts rather than peptide at all.

Impurities introduce uncontrolled variables. In analytical and in-vitro work, that uncertainty propagates directly into results. Documented, batch-specific purity is the foundation that reproducible research is built on.