Janoshik result on a Suzhou tirzepatide lot lands 4.1 points below the supplier’s figure

Janoshik has released a batch of 9 analytical reports on research-grade tirzepatide lots, including material from WXT and SGN. Reported purities range across roughly 4.1 percentage points, and the report set is unusual in stating the analytical method for every determination rather than for some of them.

Content by elemental nitrogen determination returned 92% of the labelled nominal mass, which on a 15 mg vial corresponds to roughly 14.30 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.

The Journal purchased 1800 vials from the same lot and had 9 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.

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 Alastair Renshaw, pharmaceutical supply-chain consultant. "It is the only part that tells you whether the percentage means anything."

WXT’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.