Analytical methods · 6 min read
HPLC vs. Mass Spectrometry: What Each Test Proves About a Peptide
Why a research peptide needs both HPLC purity and LC-MS identity testing, what each method measures, and how to read the results together.
Two analytical methods appear on nearly every peptide certificate: high-performance liquid chromatography (HPLC) and mass spectrometry (MS), often combined as LC-MS. They are not interchangeable. Each answers a different question, and relying on only one leaves a gap.
What HPLC measures
Reversed-phase HPLC pushes a dissolved sample through a column packed with a hydrophobic stationary phase. Molecules elute at different times depending on how strongly they interact with the column, and a UV detector records each one as a peak. The purity figure is the area of the main peak divided by the total area of all peaks.
HPLC is excellent at showing how much of a sample is one species. It cannot, on its own, prove that the main peak is the correct sequence. A different peptide of similar polarity can produce a clean single peak.
What mass spectrometry measures
Mass spectrometry ionizes the sample and measures the mass-to-charge ratio of the resulting ions. For peptides, electrospray ionization typically produces several charge states, which are deconvoluted to give the molecular mass. If the observed mass matches the theoretical mass of the intended sequence within instrument tolerance, identity is confirmed.
MS is highly specific for identity but is not a reliable quantitative purity method by itself, because different molecules ionize with different efficiency.
Reading them together
- HPLC high, MS match: the sample is pure and it is the right molecule.
- HPLC high, MS mismatch: the sample is pure, but it is the wrong molecule or a modified form.
- HPLC low, MS match: the right molecule is present alongside significant impurities.
- No MS reported: identity has not been demonstrated.
Common impurities HPLC reveals
Solid-phase peptide synthesis can leave deletion sequences (a missing residue), truncated sequences, incompletely removed protecting groups, and oxidized or deamidated forms. These typically appear as small peaks near the main peak. A published chromatogram lets a researcher judge their size directly.
North Wall reports both HPLC-UV purity and LC-MS identity for every lot. See the eight-assay panel.
Educational content for laboratory professionals. North Wall products are for in-vitro research only and are not for human or veterinary use.