HPLC vs mass spectrometry

What HPLC establishes

High-performance liquid chromatography pushes a dissolved sample through a packed column under pressure. Each component interacts with the column material differently, so the main peptide, shorter fragments and synthesis-related impurities come off the column at different times. A detector, usually ultraviolet absorbance, records each one as a peak. The area of the main peak divided by the area of all detected peaks is the figure reported as purity. Reversed-phase HPLC with UV detection is among the most widely used techniques for characterising synthetic pharmaceutical peptides, as Sharma and colleagues (2022) set out in their review of chromatographic method development.

What HPLC does not say is which molecule the main peak is. Two peptides with similar hydrophobicity can leave the column at nearly the same time, so a chromatogram with one dominant peak could in principle come from a mis-synthesised sequence or a different compound altogether. Retention time can support identity when it is matched against a reference standard, but on its own it is a separation, not a structural confirmation.

HPLC also does not measure how much peptide is in the pen. A purity figure of 98% describes the composition of what was detected in the tested sample, not the milligrams of active peptide in solution. Concentration is a separate determination with its own method; our article on what a purity percentage proves goes into that distinction.

What mass spectrometry establishes

Mass spectrometry ionises the molecules in a sample and measures their mass-to-charge ratio. For a peptide, the observed mass is compared with the theoretical mass calculated from the stated amino acid sequence. If the two agree within the instrument's tolerance, the material has the mass expected for the labelled compound. That comparison is what makes it an identity test: a sequence that differs by even one residue has a different mass, because each amino acid adds a defined increment to the total.

Mass spectrometry is not primarily a purity or quantity measurement. A sample can give a clean spectrum for the target peptide while still carrying a substantial share of unrelated material that does not ionise well under the conditions used. Nor does a mass match confirm every position in the sequence. Isomers share a mass, so a peptide with two residues swapped, or with one residue in the wrong stereochemical form, reads the same as the correct molecule. Lian and colleagues (2021), reviewing LC-MS characterisation of synthetic peptide therapeutics, single out structural isomers and epimers as the impurities that need dedicated chromatographic separation before the mass spectrometer can tell them apart.

For a combined pen such as BPC-157 & TB-500 or CJC-1295 & Ipamorelin, the identity question is doubled: both peptides have to show their expected mass.

HPLC vs mass spectrometry side by side

The two methods answer different questions, which is why they appear as separate lines on a certificate rather than as one combined quality score.

Sterility testing sits outside both. It is a microbiological test, culture-based or a validated rapid method, that looks for viable organisms in the solution and reports a pass or fail against pharmacopoeial limits. It says nothing about chemical identity or purity, and the two chemical methods say nothing about contamination. A certificate for a pre-loaded pen therefore carries three independent results: identity, purity and sterility.

Why a certificate needs both

Identity without purity tells you the right compound is present, but not in what proportion; the same spectrum could come from a sample that is 95% the labelled peptide or from one that is mostly something else. Purity without identity tells you the sample is largely one substance, but not which one. Each result leaves a gap that only the other can close.

Both gaps are realistic for a synthetic peptide. The synthesis can run cleanly on the wrong sequence, or run on the right sequence and leave it carrying truncated and deletion sequences; Lian and colleagues (2021) describe impurities arising from the starting materials, the manufacturing process and storage alike. Two routine tests cover both cases.

Analytical guidance treats the methods as complementary for the same reason. ICH Q2(R2), the harmonised guideline on validation of analytical procedures adopted in November 2023 and in effect in the EU since June 2024, lists specificity, accuracy and precision among the characteristics a validated procedure has to demonstrate, and accepts comparison with an orthogonal procedure, one that measures a different property of the same sample, as a way of demonstrating them. For a peptide, chromatographic separation and mass measurement are that orthogonal pair.

What our certificates show

Every batch is tested by an independent laboratory for identity by mass spectrometry, purity by HPLC and sterility, and the certificate for that batch is published as a plain PDF on our COA index. No account is needed to open it. Scanning the QR code on the pen takes you to the same certificate, so the batch on the label and the batch on the document are the same lot. The purity figure is the laboratory's measured result for that batch.

The certificate also states the measured concentration of the cartridge — milligrams per millilitre and the total peptide in the 3 ml — which is the content figure HPLC purity alone cannot give you. Other tests exist in pharmacopoeial practice for licensed medicinal products, such as water content, residual solvents and endotoxin; those are not part of our certificate.