AX-R09 — Impurity fingerprint shared across suppliers

A synthetic peptide lot carries a characteristic set of process impurities at characteristic levels — the deletion sequences, diastereomers and adducts left by one particular run of one particular process. Two independent syntheses of the same compound do not produce the same four impurities at the same four levels to within 0.05 % area. Two aliquots of one bulk do.

The rule matches on the named-impurity vector: same impurity identities, same rank order, and each level agreeing within 0.05 % area or 10 % relative, whichever is larger. It requires at least four named impurities, which is why nearly all matches come from PeptideMeter data — a totals-only certificate cannot be fingerprinted.

Twenty-nine matches exist in the index across 19 distinct bulks. Nothing about this is improper: contract synthesis is how the industry works and a reseller buying from a manufacturer is not doing anything wrong. But it has two consequences the index has to handle. Treating two aliquots of one bulk as two independent observations overstates the evidence, so matched batches are counted once in aggregates and cross-linked on both batch pages. And a buyer choosing between two suppliers on the basis of their published test results should know when those results describe the same material.

Where a match involves GL Biochem, the manufacturer-tier batch is treated as the parent.