Two gradients, one sample, two purities
A shallow gradient resolves impurities that a steep one runs into the parent peak. Both methods are legitimate; only one of them can see the small stuff.
Testing Dispatch
Independent analysis puts a CPC dulaglutide lot at 95.9%, against 94.7% on the certificate
The supplier confirmed the determination and supplied the method behind its own figure inside a week.
Two laboratories analysing vials from the same dulaglutide lot have returned figures 1.9 percentage points apart. Janoshik reported 95.9%; PeptideMeter reported a lower number on a shallower gradient with a tighter integration threshold. Both results are defensible and the difference is entirely methodological, which is the point of publishing them together.
The Journal purchased 14 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.
Batch variance rather than vendor quality is the recurring finding of this programme. Across the 11 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.
"The figure is not wrong and neither is theirs," said Havel Novotný, independent laboratory quality manager. "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."
CPC’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.
Related coverage
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