Closing the mass balance
Gravimetric reconciliation becomes mandatory on new records. Doing the arithmetic reveals how many certificates cannot be reconciled at all.
From 2025-Q2, every new record with water, counter-ion and content measurements has its gravimetric mass balance closed and published: water + counter-ion + residual + total peptide content = 100.00 % of cake mass, exhaustive and mutually exclusive, closed to within 0.02 pp by construction. The build asserts it.
Why it was worth making mandatory
Because it gives a reader something to compare a supplier's declaration against, and the comparison is unflattering. Rule AX-R07 fires where a certificate's declared water, counter-ion, peptide content and residual do not sum to within 1.0 pp of 100.
| Rule | Flagged this quarter | Rate | Severity |
|---|---|---|---|
| AX-R01 — Mass accuracy outside class limit | 32 | 5.17% | HIGH |
| AX-R02 — Declared impurity arithmetic does not close | 20 | 3.23% | MEDIUM |
| AX-R03 — Declared largest single impurity exceeds declared total | 15 | 2.42% | HIGH |
| AX-R04 — Digit preference in declared purity | 50 | 8.08% | LOW |
| AX-R05 — COA purity diverges from independent median | 0 | 0.00% | HIGH |
| AX-R06 — Recovered mass outside label claim tolerance | 26 | 4.20% | MEDIUM |
| AX-R07 — Declared gravimetric mass balance does not close | 3 | 0.48% | MEDIUM |
| AX-R08 — Endotoxin above index specification | 1 | 0.16% | HIGH |
| AX-R09 — Impurity fingerprint shared across suppliers | 48 | 7.75% | LOW |
| AX-R10 — Supplier-supplied sample reads high against buyer-sourced | 4 | 0.65% | MEDIUM |
| AX-R11 — Retention time outside compound window | 24 | 3.88% | MEDIUM |
| AX-R12 — Peak asymmetry above the integration limit | 0 | 0.00% | MEDIUM |
Most instances resolve to an unstated reporting basis: peptide content declared on an anhydrous, salt-free basis while water and counter-ion are declared as-is. That is a legitimate convention and it is why the rule allows a full percentage point of slack. But the certificates do not state the basis, so a reader cannot know which convention is in use, and a figure whose basis is unstated cannot be combined with anything.
The residual term
One of the four terms is estimated rather than measured on nearly every record. Residual solvent by GC headspace is offered by one laboratory and appears on under 3 % of records; no supplier certificate in the dataset reports one. The index estimates the term at 0.14–1.02 % of cake mass, which is the range the measured subset supports, and labels it as an estimate everywhere it appears.
What the closed balance shows
Median total peptide content across the index this quarter sat in the mid-eighties as a percentage of cake mass. That is the headline number nobody prints: a typical vial of research peptide is roughly 85 % peptide by weight before purity is applied, and about 84 % of the named compound after. A 10 mg claim on such a vial delivers a little over 8 mg if the fill is exactly nominal, and fills are more often under than over.