What HPLC measures
High-performance liquid chromatography (HPLC) separates components in a sample as they interact differently with a stationary phase under a defined mobile phase and detection setup. For research peptides, reverse-phase HPLC with UV detection is common.
In the CoA context, HPLC is often used to describe a purity profile: the relative peak areas of species that elute under the method’s conditions. The main peak is typically assigned to the intended peptide (or a closely related species), and other peaks may be reported as related substances or impurities when the method resolves them.
HPLC purity is therefore a method-defined chromatographic result, not a universal chemical “percent of peptide by weight” unless additional orthogonal assays support that interpretation. See also Understanding Peptide Purity Claims.
What mass spectrometry measures
Mass spectrometry (MS) measures mass-to-charge ratios of ions generated from the sample. For peptides, MS supports identity interpretation by comparing observed mass (or charge-state series) with the expected molecular mass of the target sequence or known adducts.
MS alone does not replace chromatographic purity profiling: a mass consistent with the target can coexist with isobaric or co-eluting species depending on method design. Many laboratories report HPLC for profile/purity context and MS for mass confirmation when both are available.
Why both are commonly used
- Complementary information: HPLC emphasizes separation and relative abundance under detector response; MS emphasizes mass-based identity support.
- Orthogonal checks: Agreement between a dominant HPLC peak and a mass consistent with the target sequence strengthens confidence relative to either method alone—still within the limits of the methods used.
- Procurement documentation: Research buyers often request both when institutional quality systems expect dual identity/purity evidence on a lot CoA.
What chromatograms show
A chromatogram plots detector response versus time (or volume). Peaks represent components that elute and produce a detector signal under the chosen conditions. Analysts may annotate:
- Retention time of the main peak;
- Relative peak area percentages;
- Integration windows and system suitability notes when provided;
- Wavelength or detector type (e.g., UV at a stated nm).
Co-eluting species, baseline noise, and detector response factors affect interpretation. A “clean” looking chromatogram is still method-dependent; different columns, gradients, or detection can change the observed profile.
Limitations
- HPLC area % is not automatically free-base content, salt-corrected content, or activity in a biological assay.
- MS confirmation of mass does not prove sequence purity, stereochemistry, or absence of isobaric impurities without further methods.
- Water, counter-ions, and residual solvents may require separate assays when those data are needed.
- Results apply to the tested lot and conditions; they do not authorize human or veterinary use of research materials.