The cake tells you something, and it is not purity
Dye ingress and microbial immersion are probabilistic. Vacuum decay, high-voltage leak detection and helium mass spectrometry are deterministic and far more sensitive.
Testing Dispatch
VendorInvestigate result on a Zhuhai survodutide lot lands 4.2 points above the supplier’s stated figure
The supplier confirmed the determination and supplied the method behind its own figure inside a week.
A peptide content determination commissioned by the Journal on a 5 mg survodutide vial from ERP 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 96.1%. 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 5 mg vial corresponds to roughly 10.40 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 12 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.
Purity became this trade’s single figure of merit because it is the cheapest measurement to obtain and the easiest to compare. Peptide content, which determines how much drug is actually in a vial, costs several times as much and is quoted as a priced addition by most of the twenty companies in the Journal’s dossier programme rather than carried as a standard release test. Sterility and endotoxin are separate disciplines again, and are neither tested nor claimed.
"Ask for the suitability summary before you argue about the percentage," said Dr Sirichai Boonmee, peptide chemist, Chulalongkorn University. "If the tailing factor and the replicate precision are outside limits, you are arguing about arithmetic performed on an unfit separation."ERP’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
Independent analysis puts a GL Biochem liraglutide lot at 98.5%, against 94.4% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.
What happens in solution that does not happen in the cake
Every degradation pathway accelerates by orders of magnitude on reconstitution, because the solvent that lyophilisation removed is the reagent most of them need.
MKM names the synthesis and fill sites behind its catalogue
Documentation practice is the only part of vendor quality a buyer can assess before purchase.
Six words a verification badge would need to mean anything
The Journal does not treat a badge as evidence and states so wherever it reports one.
Independent analysis puts a Homopeptide cagrilintide lot at 98.1%, against 94.7% on the certificate
The supplier confirmed the determination and supplied the method behind its own figure inside a week.