The tolerance was set by whoever wrote the certificate
The arithmetic of significant figures, applied to a document that routinely reports four of them.
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 5 mg retatrutide vial from JEEP has returned 96% of the labelled mass. Chromatographic purity on the same vial was above 97.1%. The two numbers measure different things and only one of them was on the certificate.
The Journal purchased 800 vials from the same lot and had 12 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.
Reported figures across the set were: highest 97.1%, lowest 94.3%, 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.
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 not offered as a standard release test by any of the twenty companies in the Journal’s dossier programme. Sterility and endotoxin are separate disciplines again, and are neither tested nor claimed.
"The figure is not wrong and neither is theirs," said Yusuf Kandemir, freight and customs broker, Istanbul. "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."
JEEP’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.
The arithmetic of significant figures, applied to a document that routinely reports four of them.
The supplier has not disputed the finding. It has not explained the gap either.
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
We work through a single chromatogram twice, under two integration conventions, and show where the difference comes from.
The Journal submitted the sample and paid for the analysis. The vendor was told in advance.