HPLC shows how clean a sample is. It cannot, by itself, prove that the clean peak is the peptide you think it is. That confirmation comes from mass spectrometry (MS).
The principle in one paragraph
A mass spectrometer ionises the molecules in a sample and measures their mass-to-charge ratio (m/z). Because every peptide has a precisely calculable molecular mass from its amino-acid sequence, the measured mass is a fingerprint. If the observed mass matches the theoretical mass, the identity is confirmed to within the instrument’s accuracy; if it doesn’t, something is wrong — a substitution, a deletion, or an entirely different compound.
Why identity testing is non-negotiable
Consider the GLP-1 class, where several peptides are structurally similar and command very different prices. A purity test alone could pass a mislabelled sample. This is exactly why reputable laboratories run a blind identity panel. Our GLP-1 batches, for instance, are tested with a blind assay covering semaglutide, tirzepatide and retatrutide — you can see a real example on the Retatrutide batch AS260623 report.
Measured content vs. label claim
Modern reports also quantify how much peptide is actually in the vial. A vial labelled 30 mg that measures 33.95 mg contains slightly more than stated — useful information for accurate reconstitution. We publish the measured content on every batch report alongside purity.
What to look for on a report
- A stated, expected molecular mass and a measured mass that matches it.
- An identity method named explicitly (mass spectrometry, often alongside HPLC).
- An independent laboratory and a way to verify the result directly.
Together, HPLC and MS answer the two questions that matter: is it pure? and is it what it claims to be? Once you can read both, a certificate of analysis becomes genuinely informative — which is the subject of the next guide.
