Impurity fingerprinting: nineteen bulks, twenty-nine labels
Named-impurity data reaches critical mass and the index can identify lots that are the same material sold twice.
Two independent syntheses of the same peptide do not produce the same four impurities at the same four levels. Two aliquots of one bulk do. With enough named-impurity data, that becomes a usable identification method, and in 2024-Q4 the index had enough.
The matching rule
A match requires identical impurity identities, identical rank order, at least four named impurities, and each level agreeing within 0.05 % area or 10 % relative, whichever is larger. The rule is deliberately strict; a looser rule produces coincidental matches on compounds whose impurity profiles are dominated by one or two universal species.
Twenty-nine matches were established, spanning nineteen distinct bulks. Eleven of the nineteen trace to one manufacturer-tier supplier, which is the expected result in a contract-synthesis market and not a criticism of anyone.
| Rule | Flagged this quarter | Rate | Severity |
|---|---|---|---|
| AX-R01 — Mass accuracy outside class limit | 13 | 3.00% | HIGH |
| AX-R02 — Declared impurity arithmetic does not close | 2 | 0.46% | MEDIUM |
| AX-R03 — Declared largest single impurity exceeds declared total | 0 | 0.00% | HIGH |
| AX-R04 — Digit preference in declared purity | 87 | 20.05% | LOW |
| AX-R05 — COA purity diverges from independent median | 0 | 0.00% | HIGH |
| AX-R06 — Recovered mass outside label claim tolerance | 18 | 4.15% | MEDIUM |
| AX-R07 — Declared gravimetric mass balance does not close | 16 | 3.69% | MEDIUM |
| AX-R08 — Endotoxin above index specification | 5 | 1.15% | HIGH |
| AX-R09 — Impurity fingerprint shared across suppliers | 3 | 0.69% | LOW |
| AX-R10 — Supplier-supplied sample reads high against buyer-sourced | 38 | 8.76% | MEDIUM |
| AX-R11 — Retention time outside compound window | 12 | 2.76% | MEDIUM |
| AX-R12 — Unresolved shoulder or excessive peak asymmetry | 283 | 65.21% | MEDIUM |
Two consequences the index had to handle
- Independence. Treating two aliquots of one bulk as two independent observations overstates the evidence. Matched batches are now counted once in index aggregates and cross-linked on both batch pages.
- Comparison. A buyer choosing between two suppliers on the strength of their published test results should know when those results describe the same material. Both batch pages now say so explicitly.
What fingerprinting requires, and why most data cannot supply it
A totals-only certificate cannot be fingerprinted. Of the six laboratories contributing to the index, one reports related substances by name with retention times as standard; the others report totals, or names only above a high threshold. All but four of the twenty-nine matches come from that one laboratory's data.
This is the strongest argument the index can make for named-impurity reporting. A total impurity figure tells you how much is wrong. A named table tells you what is wrong, whether it is a synthesis or a storage problem, and which other lots in the world are the same material.
Rule added
Rule AX-R09 was published this quarter with its predicate stated in full. It is classified as a low-severity flag because a shared bulk is not improper — it is an evidentiary caveat rather than a quality finding.