HPLC and Mass Spectrometry: How Peptide Purity and Identity Are Tested
HPLC estimates purity from detected peak areas; intact-mass spectrometry checks consistency with expected molecular mass. Retention-time and intact-mass matches alone do not prove full identity. HPLC purity is not peptide content by weight, and testing does not establish clinical safety or efficacy.
HPLC estimates purity from detected peak areas; mass spectrometry checks consistency with expected molecular mass. Neither an HPLC retention-time match nor an intact-mass match alone proves full molecular identity. Read the stated method and batch-specific results.
HPLC: how pure is it?
Reversed-phase HPLC pushes a dissolved sample through a column packed with a hydrophobic stationary phase, usually C18. A gradient of water and acetonitrile, typically with a little trifluoroacetic acid, elutes components at different times according to their hydrophobicity. A UV detector, commonly set at 214–220 nm where the peptide bond absorbs, records each component as a peak.
Purity is reported as the area of the main peak as a percentage of the total peak area. A clean chromatogram shows one dominant, symmetrical peak with small, well-separated impurity peaks.
What HPLC cannot tell you: it does not confirm that the main peak is the intended molecule, it can miss impurities that co-elute with the main peak, and it does not see contaminants that do not absorb UV light.
Mass spectrometry: is it the right molecule?
Mass spectrometry ionises the sample — usually by electrospray (ESI) or MALDI — and measures the mass-to-charge ratio of the resulting ions. From this the molecular mass is determined and compared with the theoretical mass of the expected sequence. A match within the instrument’s tolerance supports consistency with the expected molecular mass. A mismatch warrants investigation and may indicate a different sequence, truncation or modification.
What MS cannot tell you: on its own it is a poor measure of purity, and it cannot distinguish molecules of identical mass.
Why you need both
HPLC characterises the components detected under the stated method; intact-mass MS checks consistency with the expected molecular mass. Manufacturers commonly use both in QC. Sufficient characterization and release testing depend on the material and intended research.
Further tests worth knowing
- Net peptide content — how much of the powder’s weight is peptide, as opposed to water and counter-ions.
- Amino acid analysis — confirms composition and supports accurate quantification.
- Water content (Karl Fischer titration).
- Counter-ion content — acetate or TFA remaining from synthesis and purification.
- Endotoxin (LAL assay) — relevant for cell-based work.
Reading the results
Look for the chromatogram and the mass spectrum themselves, not just the summary figures. Check the stated method, the wavelength and the name of the laboratory. Published Aurelia batch certificates can be found in the COA Library by product or batch number.
For research use only. Not for human or veterinary use.
Sources and further reading
Evidence and limitations
An intact-mass match supports consistency with the expected molecular mass. It cannot alone establish complete sequence, stereochemistry or purity. Additional characterization and release tests depend on the material and intended research. Testing composition does not establish clinical safety or efficacy.
- Bachem: peptide analysis, salt forms and documentation, source 1
Manufacturer guidance on general peptide terminology and analytical methods; not evidence for an Aurelia batch.
- Bachem: peptide QC methods and counter-ion analysis, source 2
Describes analytical services and measurement types; the tests on a particular sample are stated in its report.
- Thermo Fisher: peptide sequencing by mass spectrometry, source 3