What is HPLC purity testing?

When a research-peptide Certificate of Analysis states a purity figure, that number almost always comes from HPLC — high-performance liquid chromatography. It's the industry-standard method for answering one specific question: how much of what's in the vial is the peptide you ordered, versus everything else?

How it works, briefly

A tiny amount of the material is dissolved and pushed under high pressure through a column packed with a specialised material. Different molecules travel through that column at different speeds, so they come out separated in time. A detector records each one as a peak on a chromatogram. The area under the main peak, as a percentage of all the peaks combined, is the purity figure — for example, 99.2%. The smaller peaks are impurities: truncated sequences, by-products of synthesis, or residual solvents.

What the number tells you

A high HPLC purity figure means the great majority of the material is the target peptide, with few contaminants. For laboratory research this matters because impurities introduce variables — anything that isn't the compound under study can affect results.

Crucially, the figure is only meaningful if it belongs to your batch. A purity result from a different lot tells you nothing reliable about the vial in your hand, which is why a certificate should always be tied to a specific lot code. You can read more about matching a certificate to a lot and verify a DNR batch here.

What HPLC does not tell you

HPLC measures purity, not identity. A sample could be highly pure and still be the wrong molecule. That's why a complete certificate pairs HPLC with mass spectrometry, which confirms the compound actually is what the label says — more on identity testing here. Purity without identity, or the other way round, only tells half the story.

HPLC also says nothing about sterility or endotoxin levels; those are separate tests.

The takeaway

An HPLC purity percentage is one of the two core numbers on a good Certificate of Analysis, and it answers "how pure?" — but only for the exact lot it was run on. At DNR Peptides every lot carries its own HPLC purity result alongside mass-spec identity, and you can check it before you buy. Browse the catalogue →