For laboratory research use only — not for human or veterinary use. View the COA library →
Analytical

HPLC-UV and LC-MS answer different questions

Jul 27, 2026 · 5 min read

Purity and identity are not the same property, and the two methods that measure them are not substitutes for one another.

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Two methods, two questions

HPLC-UV LC-MS
Answers How much of this is peptide? Is it the peptide I ordered?
Separates or measures Hydrophobicity, on a reverse-phase column Mass-to-charge ratio
Detector UV at 214 nm — sees the peptide bond Mass spectrometer
Catches Deletion sequences and other UV-active impurities, as separate peaks Single amino-acid substitutions, as a mass shift
Blind to Which peak is which What else is in the vial

Neither method substitutes for the other. Every PEPTiQX batch carries both.

Every batch we release carries both an HPLC-UV purity result and an LC-MS identity confirmation. People sometimes ask why we pay for both. The short answer is that they answer different questions.

## What HPLC-UV tells you

Reverse-phase HPLC separates components by hydrophobicity. A UV detector at 214 nm sees the peptide bond, which means it responds to essentially any peptide in the sample — your target and its deletion sequences alike. Integrating the peaks gives you a relative purity figure. What it cannot do is tell you which peak is which.

## What LC-MS tells you

Mass spectrometry measures mass-to-charge ratio. Comparing the measured mass against the theoretical monoisotopic mass of your sequence confirms you have the compound you ordered. A single amino acid substitution shifts the mass measurably — this is how sequence errors get caught.

## Why both

HPLC without MS gives you a pure unknown. MS without HPLC gives you a confirmed identity in an uncharacterised mixture. Run together, they tell you that the right molecule is present and that little else is.

Research use only. Nothing here is medical advice or a claim of therapeutic benefit. PEPTiQX products are supplied for in-vitro laboratory research by qualified professionals.

More research notes

How to actually read a certificate of analysis

A COA is only useful if you know which numbers matter. Here is what each section on a peptide certificate is telling you — and the three things people most often misread.

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Reconstitution practices that preserve your sequence

Shearing, oxidation and adsorptive loss all happen at the bench, after the material leaves our hands. A few habits prevent most of it.

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Storage, stability and what -20°C actually buys you

Lyophilised peptides are far more robust than people assume in transit, and far more fragile than people assume in solution.

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