VendorInvestigate result on a Tianjin tirzepatide lot lands 0.7 points below the supplier’s figure

VendorInvestigate has released a batch of 8 analytical reports on research-grade tirzepatide lots, including material from WWB and SSA. Reported purities range across roughly 0.7 percentage points, and the report set is unusual in stating the analytical method for every determination rather than for some of them.

Reported figures across the set were: highest 99.1%, lowest 95.3%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 8 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Content by elemental nitrogen determination returned 96% of the labelled nominal mass, which on a 10 mg vial corresponds to roughly 13.27 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 Rowena Ashcombe, community pharmacist and diabetes educator. "It is the only part that tells you whether the percentage means anything."

WWB’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.