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A purity percentage without its method is not interpretable. What "99% purity by HPLC" is (area normalization per USP <621>), the ten method parameters that must be stated beside it for the number to mean anything, why area percent is not mass percent (ICH Q2(R2) response factors; the peptide bond vs tryptophan at 214 nm), and the impurity classes — counterion, water, residual solvents, inorganics, co-eluting species — that a chromatographic purity figure never sees.