Three questions, several methods
Analytical characterization answers three separate questions about a peptide batch, and no single measurement answers all three. Laboratories use different method sets, and the tests performed vary by lot — the batch certificate states which were run and what they reported.
- HPLC — how pure is it? (area percentage of the target peak).
- Identity — is it the expected molecule? (typically comparison against a reference standard).
- Content — how much active material is present, distinct from gross fill?
HPLC: purity
Reversed-phase HPLC separates the components of a sample by hydrophobicity and reports the target peak as a percentage of total area. A purity of 98% or higher is typical for research-grade peptides, but the number is only meaningful alongside the method that produced it.
Identity confirmation
Identity is confirmed by comparing the material against a reference standard — matching retention time and UV spectrum to a known reference, for example. Some laboratories add mass spectrometry, which measures the mass-to-charge ratio of ionized molecules and confirms the expected molecular weight. A purity figure cannot catch a sequence error or a salt mismatch — an identity measurement can.
Content: active material vs. gross fill
Content — how much active peptide is in the vial, distinct from gross fill weight — is reported as its own value. Laboratories determine it by different routes, including amino acid analysis, which hydrolyzes the peptide and quantifies the released residues. The certificate states the method used for the lot, so a stated mass can be tied to actual active material.
Why one number is not enough
A single purity percentage does not confirm identity, nor does it tell you how much active peptide is in the vial. A documented batch reports purity, identity, and content together so each can be checked independently.