Analytical control of a synthetic peptide uses orthogonal methods: one class of test to assign identity, another to estimate purity, and lot records to show the same methods were applied again.
Identity is not purity
Mass spectrometry or a validated identity chromatogram answers whether the principal species is the intended sequence. A 99% HPLC area-percent on the wrong sequence is a failed lot, not a better lot.
Purity is method-bound
Changing column, gradient, or detection wavelength can change area-percent. Lot-to-lot comparison is only meaningful when the method is stated and held constant, or when a method change is documented.
Assay versus purity
If an assay or net peptide content is reported, it is a different number from HPLC purity. Do not average them and do not treat them as interchangeable acceptance criteria.
What consistency means for a supplier
Consistency is the ability to issue a new lot with the same identity fields, the same or documented analytical methods, and a COA whose lot number matches the container. A recycled PDF from an older lot is not evidence of consistency.
Receiving language
Write acceptance criteria in methods, for example HPLC area-percent at the stated method, and MS consistent with calculated mass. Do not write adjectives such as high purity as if they were tests.
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