HPLC vs mass spectrometry: two questions, two tests
For research use only. Not for human or animal consumption.
People often ask which is better, HPLC or mass spec. For a peptide COA that is a bit like asking whether a ruler is better than a scale. They measure different things, and a report that has only one of them leaves a real gap.
The short version
| HPLC (with UV detection) | Mass spectrometry | |
|---|---|---|
| Question it answers | How much of the sample is the main component? | What is the mass of the component? |
| What it reports | Area percent purity | Observed mass, compared to the expected mass |
| What it measures | UV absorbance over time as the sample separates | Mass-to-charge ratio of ions |
| Blind spot | Does not identify the peak | Does not give a reliable purity percentage |
What HPLC shows, and what it cannot
HPLC separates a sample into its components and measures each one as it leaves the column. The purity figure is the main peak's share of all the peak area.
What it cannot do is say what that main peak is. A wrong sequence, made and purified well, would give a lovely single peak. So would a different peptide entirely. HPLC sees "one thing, mostly," not "the right thing."
What mass spec shows, and what it cannot
Mass spectrometry turns molecules into ions and sorts them by mass-to-charge ratio (m/z). For a peptide, the lab compares the observed mass to the theoretical mass calculated from the sequence. A match within the instrument's tolerance is strong evidence that the expected molecule is present.
What it cannot do well on its own is say how much. Different molecules ionize with different efficiency, so a small impurity can give a big signal or a large one a small signal. A spectrum dominated by the right mass does not mean the sample is 99% that mass.
Why a good COA has both
Put the two together and they cover each other's blind spots:
- HPLC: the sample is about 99% one component.
- Mass spec: that component has the expected mass.
Neither one alone gets there. A report with HPLC only is a large unnamed peak. A report with mass spec only is a confirmed identity with an unknown purity.
Where the two meet: LC-MS
Many labs run the two in one instrument, with the HPLC column feeding the mass spectrometer. That is LC-MS, and it can assign a mass to each peak in the chromatogram, including impurities. It is a different setup from separate HPLC-UV and MS tests, with its own trade-offs; that comparison has its own page.
What neither one covers
Neither test measures net peptide content, endotoxin, microbial status or metals. Those need their own assays, and they appear as their own rows on a COA when they were run.
FAQ
Can mass spec detect impurities?
It can see many of them, especially when coupled to chromatography, but its signal is not a reliable measure of how much impurity is present.
Is a mass match enough to trust a peptide?
It confirms identity, not purity or content. Pair it with HPLC purity and, where relevant, content and contaminant tests.
What about NMR?
NMR can give structural detail and is sometimes used for content against a standard. It is less common on routine peptide COAs.
Research use only
Peptira supplies materials for laboratory research. For research use only. Not for human or animal consumption. Not for diagnostic or therapeutic use. This page compares analytical methods. It is not medical advice.