Janoshik result on a Suzhou tirzepatide lot lands 4.1 points above the supplier’s stated 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 96% 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 16 vials from the same lot at retail and had four 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.

Dr Wenjun Xie, process chemist and peptide manufacturing consultant, wanted the wavelength printed. "A method reading at 280 nanometres cannot see a fragment that has lost its aromatic residue. That is not a failure of the laboratory, it is a fact about the question they were asked."

WXT’s dossier has been updated with this determination and with the company’s response to it. The dossier’s ordering box records the lead times, the minimum quantities and what a buyer should ask for at the point of order.