HPLC Purity Explained: What “≥99%” Really Means

You'll see purity claims on nearly every research compound — but a number alone doesn't mean much without context. Here's what HPLC purity actually tells you.

What HPLC measures

High-Performance Liquid Chromatography (HPLC) separates the components of a sample as they pass through a column at different speeds. A detector records each component as a peak. The area of the target compound's peak, divided by the total area of all peaks, is reported as the purity percentage.

So "99.4% purity by HPLC" means ~99.4% of what the instrument detected was the intended compound, and ~0.6% was other, process-related material.

Specification vs. result

A COA lists two things:

• Specification — the minimum standard the batch must meet (e.g. ≥95.0%)
• Result — what this batch actually measured (e.g. 99.4%)

A batch "passes" when the result meets or beats the spec. A high result against a clear spec is what you want to see.

Why the method matters

"Purity" with no method is close to meaningless. HPLC at a stated wavelength (e.g. UV 214 nm) is the standard for peptides. Be cautious of purity figures that don't say how they were measured.

What purity does not tell you

Purity is not the whole picture. It doesn't cover identity (is it the right molecule?), net peptide content (how much peptide vs. salt/water?), or contaminants (heavy metals, endotoxin, sterility). A complete COA reports all of these alongside purity.

Bottom line

Look for a high result against a stated spec, measured by HPLC, on a lot-specific certificate — and read it next to the identity and contaminant results, not on its own.

For laboratory research use only. Not for human or veterinary use.