If you have read a few certificates of analysis, you will have seen the same two abbreviations again and again: HPLC and MS. Shops quote them, labs list them, forums argue about them. They are often mentioned in the same breath, as if they were two names for one test. They are not. They answer different questions, and a report that offers only one of them is telling you half the story.
The short version
- HPLC (high-performance liquid chromatography) answers: how much of this sample is one compound, and how much is something else? It is the source of the purity percentage.
- MS (mass spectrometry) answers: what is the mass of the molecules in this sample — and does it match the peptide on the label? It is the basis of the identity check.
A sample can be 99% pure and still be the wrong peptide. A sample can be the right peptide and only 80% pure. You need both answers.
How HPLC works, in plain terms
The sample is dissolved and pushed under pressure through a column packed with fine material. Different molecules travel through the column at different speeds, so they come out at different times. A detector — usually measuring UV light absorption — records a signal as each one exits.
The result is a chromatogram: a line with peaks. Each peak is something the detector saw. The area under the main peak, divided by the area under all peaks, gives the purity figure you see on the certificate.
What HPLC is good at:
- Showing whether there is one dominant compound or several.
- Detecting related impurities, such as shortened sequences, that separate from the main peak.
- Giving a repeatable number that can be compared between batches.
What HPLC cannot do on its own:
- It cannot tell you which molecule the main peak is. A wrong compound can produce a clean, single peak.
- It only “sees” what the detector responds to at the chosen wavelength. Water, many salts and some contaminants are invisible to it.
- The purity percentage depends on method choices — column, gradient, wavelength. Two labs can report slightly different numbers for the same batch.
How mass spectrometry works, in plain terms
Mass spectrometry turns molecules into charged particles and measures their mass-to-charge ratio. For peptides, the lab compares the observed mass with the expected mass calculated from the sequence. If they agree within the stated tolerance, the identity is confirmed.
What MS is good at:
- Confirming that the main compound has the right molecular mass.
- Spotting compounds with the wrong mass — a different peptide, a modified one, or a fragment.
What MS cannot do on its own:
- A standard MS result is not a purity measurement. It can show that the right molecule is present without telling you how much of the sample it makes up.
- Two different molecules with the same mass would not be told apart by mass alone.
Why the best reports combine them
Many labs run LC-MS: the HPLC separation feeds straight into a mass spectrometer, so each peak can be both measured and identified. When a certificate shows an HPLC chromatogram and an MS identity result with numbers, you have the two halves of the picture.
When you read a report, look for:
- An HPLC section with a chromatogram and a purity percentage.
- An MS section with expected and observed mass.
- The same batch number on both.
What this means when you shop
Our purity & testing criterion — the heaviest in our scoring, at 30% — rewards shops that publish this kind of documentation per batch. Right now, that column is thin across our partner list. Nexo Research has not published lab reports yet, and we found no public reports for Europa-Peptide; in our facts tables both read “not published” for lab testing.
That is not the same as saying their products fail any test. It means the evidence isn’t public, so the burden shifts to you as the buyer: ask for the batch COA, and check that it contains both an HPLC result and an MS identity result. If a shop sends only a purity number, ask whether an identity test was run. A good shop will know what you mean.
A note on numbers that look too good
A chromatogram with a single needle-thin peak and “99.9%” printed beside it is not automatically suspicious — but a set of certificates where every product, every batch, shows exactly the same figure should make you curious. Real measurements wobble. Repeated identical numbers are worth a polite question.
The takeaway
HPLC tells you how clean the sample is. MS tells you what it is. One without the other is half a receipt. When you see both, with matching batch numbers and a named lab, you are reading the kind of paperwork that earns points in our ledger.
Products sold by these shops are for laboratory research use only. Nothing in this article is medical advice.