PeptideMeter result on a Changsha liraglutide lot lands 3.8 points above the supplier’s stated figure

PeptideMeter has published a purity determination of 98.2% on a 30 mg vial of liraglutide supplied by BCH, against a figure of 96.4% on the certificate that accompanied the vial. The sample was submitted by the Journal in May 2024 as part of a continuing programme of arm’s-length purchasing, and the vendor was told before the order was placed that any result would be published.

Content by elemental nitrogen determination returned 99% of the labelled nominal mass, which on a 30 mg vial corresponds to roughly 13.31 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 13 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.

"The figure is not wrong and neither is theirs," said Dr Emiko Tanabe, mass spectrometrist. "They are answers to two different questions and the trade has decided to pretend there is only one question. Print the gradient and the argument disappears."

BCH’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.