HPLC & Mass Spec Testing Explained

Two analytical methods sit behind almost every credible purity claim in peptide research: high-performance liquid chromatography (HPLC) and mass spectrometry (MS). They measure different things, and a proper quality check uses both together. Understanding what each one actually does makes a Certificate of Analysis far easier to interpret.

What HPLC Measures

HPLC separates the components of a sample by pushing it, dissolved in a solvent, through a densely packed column under high pressure. Different molecules travel through the column at different speeds depending on their chemistry, so they emerge at different times. A detector records each as a "peak" on a chromatogram. For a peptide sample, the target compound should show as one dominant peak; smaller peaks represent impurities or related substances. Purity is calculated from the relative area of those peaks.

In short: HPLC answers the question "how much of this sample is the thing I want, versus everything else?"

What Mass Spectrometry Measures

Mass spectrometry answers a different question: "is this actually the right molecule?" It ionises the sample and measures the mass-to-charge ratio of the resulting fragments, producing a highly accurate molecular weight. Because every peptide has a known theoretical mass based on its amino acid sequence, MS can confirm whether the material matches the intended compound — something HPLC alone cannot do.

Why Both Are Needed

The two methods cover each other's blind spots. HPLC can tell you a sample is 99% pure but not what it actually is; MS can confirm identity but isn't the primary tool for quantifying trace impurities. A sample could, in principle, be highly pure yet be the wrong peptide entirely — which is why a CoA that shows HPLC purity and MS identity together is far more trustworthy than one showing either alone.

To see how these results are presented in practice, read our guide on how to read a Certificate of Analysis.