Independent analysis puts a WXT exenatide lot at 96.5%, against 92.6% on the certificate

A peptide content determination commissioned by the Journal on a 2 mg exenatide vial from WXT has returned 97% of the labelled mass, the balance being the counter-ion and residual water that every lyophilised salt carries. Chromatographic purity on the same vial was above 96.5%. The two numbers measure different things, and this is one of the few certificates in the trade to print both.

Content by elemental nitrogen determination returned 97% of the labelled nominal mass, which on a 2 mg vial corresponds to roughly 7.94 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, 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."

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.