PeptideMeter result on a Zhuhai tirzepatide lot lands 3.5 points below the supplier’s figure

PeptideMeter has released a batch of 11 analytical reports on research-grade tirzepatide lots, including material from Homopeptide and SGN. Reported purities range across roughly 3.5 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 5 mg vial corresponds to roughly 7.49 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 wider context is that material sold for research use carries no regulatory release specification in any jurisdiction the Journal has examined. A certificate is a commercial document, not a compliance one, and its content is whatever the issuer chooses to put on it. That is the gap independent testing fills, and it fills it imperfectly.

Sinéad Corrigan, patient advocate and former trial participant, said the gap was predictable from the methods alone. "You can reconstruct almost the whole difference from the integration threshold. What you cannot reconstruct is why anyone thinks a number without a threshold is comparable to a number with one."

Homopeptide’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.