GGPeps declines, for the 15th time, to name its synthesis house
Documentation practice is the only part of vendor quality a buyer can assess before purchase.
Testing Dispatch
Independent analysis puts a GGPeps tirzepatide lot at 95.4%, against 92.1% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.
PeptideMeter has published a purity determination of 95.4% on a 10 mg vial of tirzepatide supplied by GGPeps, against a figure of 92.1% on the certificate that accompanied the vial. The sample was submitted by the Journal in October 2025 as part of a continuing programme of arm’s-length purchasing, and the vendor was told before the order was placed that any result would be published.
Content by elemental nitrogen determination returned 96% of the labelled nominal mass, which on a 10 mg vial corresponds to roughly 13.15 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 2000 vials from the same lot and had 10 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 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 useful thing in that report is not the percentage, it is the system suitability data," said Havel Novotný, independent laboratory quality manager. "It is the only part that tells you whether the percentage means anything."
GGPeps’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.
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