Independent analysis puts a JEEP tirzepatide lot at 96.0%, against 92.6% on the certificate

Janoshik has released a batch of 13 analytical reports on research-grade tirzepatide lots, including material from JEEP and SGN. Reported purities range across roughly 0.9 percentage points, and the report set is unusual in stating the analytical method for every determination rather than for some of them.

The Journal purchased 200 vials from the same lot and had 13 of them analysed separately, in order to distinguish vial-to-vial variation from method variation. Vial-to-vial agreement was within 0.4 percentage points. Method-to-method disagreement was an order of magnitude larger.

Content by elemental nitrogen determination returned 94% of the labelled nominal mass, which on a 15 mg vial corresponds to roughly 5.15 mg of peptide rather than the labelled figure. The remainder is accounted for by counter-ion, residual water and residual solvent, none of which is visible chromatographically.

Discrepancies of one to two percentage points between a supplier’s figure and an independent determination are common and usually explicable: a faster gradient resolves fewer impurities, a higher integration threshold discards more small peaks, and a wider solvent-front exclusion window removes early-eluting fragments from the calculation altogether. None of that is misconduct. All of it is invisible unless the method is disclosed.

"The useful thing in that report is not the percentage, it is the system suitability data," said Lorcan Feeney, analytical services director at an independent laboratory. "It is the only part that tells you whether the percentage means anything."

JEEP’s dossier has been updated with this determination and with the date of the request for comment. The dossier’s "what we could not verify" box records the questions still outstanding.