How identity is confirmed
Purity and identity are different questions. This is how a laboratory establishes that the material is what the label says.
A purity figure tells you that a sample is overwhelmingly one single substance. It does not, on its own, tell you which substance. A vial could be highly pure and still be the wrong peptide. Identity confirmation is the separate step that closes that gap.
Why it is a separate question
Chromatography separates components and measures their relative proportions. It is excellent at that. What it cannot do by itself is tell you the molecular identity of the thing producing the main peak — only that one thing dominates the sample.
Confirming identity means establishing that the dominant component has the molecular properties expected of the named compound.
Comparison against a reference standard
The most direct approach is comparison with a known reference standard: a sample of the compound whose identity has already been established. The unknown and the reference are run under identical conditions, and the question is whether they behave identically.
A compound’s retention time — how long it takes to travel through the column — is characteristic under fixed conditions. If the test sample and the reference standard elute at the same point, and co-injecting the two produces a single peak rather than two, that is strong evidence they are the same substance.
This is the basis on which identity is confirmed for the material we supply: tested against a reference standard rather than asserted from the label.
Other methods you will encounter
Mass spectrometry measures the mass-to-charge ratio of a molecule and can confirm that an observed molecular weight matches the theoretical weight for a stated sequence. Amino acid analysis hydrolyses the peptide back to its constituent amino acids and confirms the expected ratios. Sequencing methods read the order of residues directly.
These are standard laboratory techniques and you will see them referenced on certificates from various suppliers. Which methods were applied to a given batch is stated on that batch’s own certificate — it is worth checking rather than assuming.
What to look for
On any certificate, identity and purity should be reported as distinct findings with the method named for each. A document that reports a purity percentage and says nothing about identity has answered half the question.