When a certificate says a peptide is "99.1% pure", it almost always means HPLC purity: the main peak's share of the total peak area in a chromatogram, measured by UV absorbance.
What it measures
Reversed-phase HPLC separates the target peptide from closely related impurities, such as chains missing a residue (deletion sequences), truncated chains, or chains with a damaged side chain. The purity figure is how much of the UV-absorbing material belongs to the target peak.
What it does not measure
- Net peptide content. Freeze-dried peptides also contain water and counter-ions (often acetate or trifluoroacetate). A vial can be 99% pure by HPLC and still be about 70–90% peptide by weight. A separate content or quantity test measures this.
- Identity. A single clean peak could, in principle, be the wrong molecule. Mass spectrometry confirms identity.
- Anything that does not absorb UV at the wavelength used, such as salts.
Why blends have no single purity figure
A blend contains several intended compounds, so one main-peak percentage is meaningless. For blends, we report identity and quantity of each component instead.
Why we never show a purity figure without a document
A purity figure is only meaningful when it is tied to a specific lot's certificate. That is why our products show "COA pending" until the certificate is published.
Quick quiz
For laboratory research use only. This article describes chemistry and handling. It does not describe human use.