Purity asks how much of the chromatogram belongs to the principal component
Chromatographic purity is method-dependent and generally reflects the relative signal assigned to the principal peak under stated conditions.
Identity asks what the molecule is
Mass spectrometry, sequence-related methods, and other orthogonal techniques can provide evidence that the principal material matches the expected molecular identity.
Content asks how much target material is actually present
Net peptide content or assay can address a different question from chromatographic purity. A high purity percentage does not automatically mean the vial contains an equivalent percentage of target peptide by total mass.
Procurement implication
Strong documentation clearly states which analytical question each test answers rather than using one number as a universal quality claim.