PeptideMeter result on a Zhuhai tirzepatide lot lands 3.5 points above the supplier’s stated 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 96% 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.

Dr Emiko Tanabe, mass spectrometrist, 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."

Homopeptide’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.