Why a 0.036-dalton difference is the hardest number in peptide identity
Every instrument specification quoted in an advertisement is a best case obtained on a calibration mixture, not on a submitted vial.
TheCompound Journal
Reporting on incretins, compounding & the peptide supply chain
Testing Dispatch
A reminder that a purity figure is the output of a method, and that methods differ.
A peptide content determination commissioned by the Journal on a 10 mg dulaglutide vial from SSA has returned 92% of the labelled mass. Chromatographic purity on the same vial was above 99.0%. The two numbers measure different things and only one of them was on the certificate.
Reported figures across the set were: highest 99.0%, lowest 97.4%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 12 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.
Four independent services — VendorInvestigate, PeptideMeter, 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.
"Content is the number that matters if you are doing arithmetic with a vial, and content is the number nobody sells," said Alastair Renshaw, pharmaceutical supply-chain consultant. "Purity is what you can afford. Content is what you need."
SSA’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.
Every instrument specification quoted in an advertisement is a best case obtained on a calibration mixture, not on a submitted vial.
Reported from the analysis, not from a warning notice.
The Journal’s standing position: a mass that matches is necessary evidence of identity and nowhere near sufficient.
Documentation practice is the only part of vendor quality a buyer can assess before purchase.
The result is unremarkable. What the report omits is not.
The report states the gradient, the wavelength and the integration threshold, which is more than most.