HPLC Purity Standards for Research Peptides

HPLC purity is the single most-reported metric on a peptide COA. It is also one of the most misunderstood. This article explains what the headline percentage actually represents, how the underlying chromatogram is read, and why third-party verification is the only meaningful guarantee.

What HPLC measures

High-performance liquid chromatography separates the components of a mixture by their interaction with a stationary phase under high pressure. For peptides, the standard configuration is reversed-phase HPLC: a hydrophobic C18 stationary phase, with elution by a gradient of acetonitrile in water acidified with trifluoroacetic acid. UV detection at 220 nm captures the peptide bond absorbance.

Reading the chromatogram

The chromatogram is a plot of detector response (absorbance) against retention time. The peptide of interest appears as a peak. Smaller peaks before or after represent impurities — typically truncated sequences, deletion products, oxidation products, or residual reagents.

Purity is calculated as the area under the main peak divided by the total integrated area, expressed as a percentage. A clean main peak with a narrow base and a flat baseline is what a well-purified peptide looks like.

The 98% standard

The conventional threshold for research-grade peptides is ≥98% by HPLC. Below this, contaminants begin to interfere with downstream assays. Above approximately 99.5%, the cost of further purification rises sharply while incremental experimental benefit drops. The Pillar Research catalogue averages above 99%; individual batches are reported to 0.1% precision on the COA.

Common impurity profiles

• Deletion peptides — sequences missing one residue, typically eluting close to the main peak
• Truncation products — sequences missing several N-terminal or C-terminal residues, eluting earlier
• Oxidation products — methionine or tryptophan oxidation, +16 Da per oxygen, eluting earlier than the main peak
• Acetate / TFA salt counter-ions — these affect peptide content but not HPLC purity per se; they are reported separately

Third-party verification

A manufacturer-only COA is a self-report. Third-party verification — analysis by an independent laboratory with no commercial interest in the result — is the only credible guarantee. Pillar Research uses an independent Australian laboratory for every batch. We do not conduct in-house testing, and we will not release material on the basis of a manufacturer COA alone.

For a full walkthrough of what a complete COA contains and the red flags that mark sub-standard supply, see our COA reading guide.