HPLC purity is the area-percent of a target compound’s peak relative to all UV-detectable peaks in a chromatogram. A peptide listed at 99% HPLC purity means the target peptide accounts for 99% of the UV-absorbing material detected by the HPLC column at the analytical wavelength (typically 214 nm or 280 nm for peptides).
What ≥99% Actually Means
HPLC purity does not measure mass purity. It measures the proportion of UV-active material that is the target compound. UV-inactive impurities (water, salts, ions that don’t absorb at the detection wavelength) don’t appear in the chromatogram and don’t affect the percentage.
For most research peptide work this distinction is fine — UV-active impurities (other peptides, fragments, racemized isomers) are exactly the contaminants that would interfere with biological assays.
The Tiers
- ≥99%: research-grade standard for most compounds.
- ≥99.5%: achievable for shorter peptides; worth specifying for sensitive assays.
- 95–99%: acceptable for preliminary screening but not strictly research-grade.
- Below 95%: not research-grade. The unidentified material can interfere with results.
How to Verify
A research-grade supplier publishes a per-lot HPLC chromatogram, addressable by the lot number on the vial label. Without lot-specific documentation, the purity claim is marketing material — not data.
For deeper detail, read How to Read an HPLC Chromatogram. The full Matte COA library is at /coas/.
Research use only. Not for human consumption. Statements not evaluated by the US FDA.