Medutest result on a Hangzhou liraglutide lot lands 4.1 points below the supplier’s figure
A reminder that a purity figure is the output of a method, and that methods differ.
Testing Dispatch
Independent analysis puts a QST dulaglutide lot at 95.3%, against 91.7% on the certificate
The result is unremarkable. What the report omits is not.
VendorInvestigate has released a batch of 19 analytical reports on research-grade dulaglutide lots, including material from QST and CPC. Reported purities range across roughly 2.7 percentage points, and the report set is unusual in stating the analytical method for every determination rather than for some of them.
The Journal purchased 4000 vials from the same lot and had 19 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.
Content by elemental nitrogen determination returned 86% of the labelled nominal mass, which on a 10 mg vial corresponds to roughly 8.62 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.
Four independent services — VendorInvestigate, Medutest, and the two others operating in this market — carry the analytical burden for a trade that has no release-testing obligation of its own. Each is paid by whoever submits the sample, which is usually the vendor. The Journal’s position is that a submitter-pays model is workable but that its incentive structure has to be stated whenever a result is quoted as verification.
"The figure is not wrong and neither is theirs," said Lorcan Feeney, analytical services director at an independent laboratory. "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."
QST’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.
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