HPLC vs Mass Spectrometry: How Peptides Are Tested

Two different measurements answering two different questions. What each one establishes and why a certificate reports both.

Two different questions

These are not competing methods and a certificate should report both, because they answer different things.

HPLC asks: how much of this is the target? Mass spectrometry asks: is the target what we think it is? Either on its own leaves an obvious gap.

What HPLC establishes

High-performance liquid chromatography separates a mixture by pushing it through a column; different molecules move at different speeds and emerge at different times. A detector records what comes off and when, producing a chromatogram of peaks.

Integrating the area under those peaks gives the purity figure. A single sharp peak accounting for nearly all the area indicates one dominant substance. Several peaks indicate a mixture, and their relative areas indicate the proportions.

What mass spectrometry establishes

Mass spectrometry ionises the sample and measures mass-to-charge ratio, giving the molecular weight of what is present. Compared against the weight calculated from the molecular formula, it confirms identity.

This is the check that catches a substituted compound. A vial could contain a single very pure substance that is not the peptide ordered — HPLC would report excellent purity and be entirely correct. Only the mass tells you which molecule it is.

What neither establishes

Both are composition measurements. Neither says anything about sterility, bacterial endotoxin, or heavy metals — those require separate assays that are not part of a standard purity and identity report.

And neither is a statement about suitability for any use outside a laboratory.