Most peptide certificates rely on two techniques: high-performance liquid chromatography (HPLC) and mass spectrometry (MS). They answer different questions, and neither one is enough by itself.
HPLC: how pure is the sample?
HPLC pushes the dissolved sample through a packed column under high pressure. Different components travel through the column at different speeds, so they come out at different times (their retention times). A UV detector, typically set around 214–220 nm where peptide bonds absorb, records each component as a peak.
Purity is the area of the main peak divided by the total area of all peaks. A result of 99.8% means 99.8% of the UV signal came from the main component.
What HPLC does not tell you:
- Identity. A peak shows that something came off the column at a certain time, not what it is.
- Net peptide content. Lyophilised peptides also contain water and counter-ions (such as acetate or TFA) that HPLC-UV doesn’t count. A sample can be 99% pure by HPLC and still be less than 100% peptide by weight.
- Impurities that overlap or are invisible. Impurities that come off at the same time as the main peak, or that don’t absorb UV, can be missed.
Mass spectrometry: is it the right molecule?
MS ionises the sample and measures the mass-to-charge ratio (m/z) of the ions. Peptides often carry several charges, so they show up as a series of peaks that can be converted back into one molecular mass. If the observed mass matches the theoretical mass (for example, 639.8 g/mol for SS-31), the identity is confirmed.
What MS does not tell you on its own:
- How much of each component is there. MS signal depends on how easily each molecule ionises, so it isn’t a direct measure of purity.
- Isomers. Molecules with the same mass, such as some sequence variants, can need extra methods (fragmentation, MS/MS) to tell apart.
LC-MS: both at once
Many labs connect the two (LC-MS), so each HPLC peak is also checked by mass. This confirms that the main peak really is the target compound.
HPLC-MS and LC-MS/MS: what the abbreviations mean
You will see the combined method written several ways: HPLC-MS, LC-MS, HPLC-MS/MS or LC-MS/MS. They all describe the same idea: the outlet of the chromatography column feeds straight into a mass spectrometer, so every peak the column separates also gets a measured mass.
The single MS version measures the mass of each intact molecule. The MS/MS (tandem) version goes one step further: it isolates one ion, breaks it into fragments and measures those fragments. For a peptide, the fragment pattern follows the amino-acid sequence, so MS/MS can confirm not just the total mass but the order of the residues.
| Method | What it measures | Question it answers |
|---|---|---|
| HPLC (UV detector) | Peak areas at 214 to 220 nm | How pure is the sample? |
| MS | Mass of the intact molecule | Is the main peak the right molecule? |
| HPLC-MS / LC-MS | Retention time plus mass for each peak | Purity and identity in one run, and what the impurities are |
| LC-MS/MS | Fragment masses of a selected ion | Is the sequence correct, residue by residue? |
Common questions about HPLC and mass spectrometry
Is HPLC the same as LC?
HPLC is a form of liquid chromatography (LC) run at high pressure through a tightly packed column, which gives sharper separation. UHPLC uses even higher pressure and smaller particles. On a certificate, LC-MS and HPLC-MS usually refer to the same setup.
Why is purity reported from the UV trace and not the mass spectrum?
Different molecules ionise with very different efficiency, so the size of a peak in the mass spectrum does not reliably reflect how much of that substance is present. UV absorbance at the peptide bond is far more uniform across peptides, which is why purity percentages come from the HPLC-UV trace.
What does ESI mean on a mass spectrometry report?
Electrospray ionisation (ESI) is the gentle ionisation method most often used for peptides. It tends to produce ions carrying several charges, so a report may list values such as [M+2H]2+ or [M+3H]3+. These are the same molecule seen at different charge states, and the software converts them back to one molecular weight.
Can HPLC alone confirm identity?
Not on its own. A retention time that matches a reference standard is supporting evidence, but two different molecules can elute at almost the same time. Mass spectrometry is what confirms the molecule is the one on the label.
What to look for on a certificate
- A purity figure and an identity confirmation.
- The method named for each (for example “HPLC” and “ESI-MS”).
- Ideally, the chromatogram and the observed mass, not just a pass or fail.
Our Bioviridian certificates in the COA Bank report both HPLC purity and mass-spectrometry identity for each batch. New to certificates? Start with How to read a COA.
Research use only
Isla Longevity supplies research compounds for laboratory use only. They are not approved by the FDA for human or veterinary use and are not for human consumption. This article explains analytical testing and is not medical guidance.
