Independent analysis puts a SGN semaglutide lot at 96.6%, against 94.9% on the certificate

A peptide content determination commissioned by the Journal on a 30 mg semaglutide vial from SGN has returned 94% 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 96.6%. The two numbers measure different things, and this is one of the few certificates in the trade to print both.

The Journal purchased 17 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.

Content by elemental nitrogen determination returned 94% of the labelled nominal mass, which on a 30 mg vial corresponds to roughly 13.79 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.

Batch variance rather than vendor quality is the recurring finding of this programme. Across the 17 determinations the Journal has commissioned to date, within-vendor spread has been wider than between-vendor spread for two thirds of the companies tracked, which is an argument against rating any supplier on a single number.

Marek Doležal, analytical chemist and former QC laboratory manager, 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."

SGN’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.