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Understanding HPLC Purity Certificates

Research Team · August 15, 2026 · 5 min read

Any supplier can print 99% on a label. A certificate of analysis (COA) is what lets a researcher check that number. Knowing how to read one is one of the most useful skills when sourcing research peptides.

What HPLC measures

High-performance liquid chromatography (HPLC) separates the components of a sample as they pass through a column. A detector, typically measuring UV absorbance at around 214 to 220 nm where the peptide bond absorbs, records each component as a peak on a chromatogram. Purity is the area of the main peak expressed as a percentage of the total peak area.

A figure of 99% therefore means roughly 99% of the UV-absorbing material in the sample is the main peak. It does not, by itself, say what that peak is.

Purity is not the same as identity

HPLC tells you how much of the sample is one compound, not which compound it is. Identity is normally confirmed by mass spectrometry (MS), which measures the molecular mass. A trustworthy COA reports the observed mass alongside the theoretical mass for the expected sequence, and the two should agree within instrument tolerance.

Purity is not the same as peptide content

A lyophilised peptide is not 100% peptide by weight. It contains counter-ions left over from synthesis and purification, most commonly trifluoroacetate (TFA) or acetate, plus residual water. Net peptide content describes the proportion of the powder that is actually peptide. Two batches with the same HPLC purity can differ in net content, which matters when preparing solutions of a defined concentration.

What to look for on a COA

  • The compound name and, ideally, its sequence or molecular formula.
  • A batch or lot number that matches the vial you received.
  • The test date, and the name of the laboratory that ran the analysis.
  • The HPLC purity percentage, with the chromatogram itself attached.
  • Mass spectrometry results showing observed mass against theoretical mass.

Red flags

  • No batch number, so the report cannot be tied to the product.
  • A chromatogram with no axes, no retention time or no visible baseline.
  • Identical certificates reused across different batches or different compounds.
  • A purity figure with no accompanying identity data.

Independent testing

The strongest assurance is a COA from a third-party laboratory rather than the manufacturer itself, because it removes the conflict of interest. If a batch matters to your work, ask for its certificate and check that it matches the lot you hold.

All products are supplied strictly for in-vitro laboratory research by qualified professionals and are not for human or animal consumption.