Anyone reading a peptide COA
HPLC vs LC-MS quick reference
One page: what each method establishes, what it does not, and which question you are actually asking.
Updated 12 September 2026 · No sign-up required
Print this beside a certificate. If the document does not state the method, stop — a bare percentage is a claim, not a measurement.
HPLC (usually RP-HPLC, UV)
- Asks: what share of detected peak area is the main peak?
- Does not ask: what is the peak, or what share of mass is peptide.
- Need: method, wavelength, chromatogram, integration basis.
LC-MS
- Asks: was a mass consistent with the expected ion observed?
- Does not ask: how pure is the sample.
- Need: observed value, not only “conforms”.
When you need both
- Purity without identity is compatible with a pure wrong substance.
- Identity without purity is compatible with a correct mass on a minority peak.