Independent analysis puts a GL Biochem semaglutide lot at 97.8%, against 94.6% on the certificate

PeptideMeter has published a purity determination of 97.8% on a 10 mg vial of semaglutide supplied by GL Biochem, against a figure of 94.6% on the certificate that accompanied the vial. The sample was submitted by the Journal in November 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.

The Journal purchased 11 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.

The Journal purchased 11 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 9 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 gap that matters is not between the two laboratories, it is between either of them and the certificate," said Marek Doležal, analytical chemist and former QC laboratory manager. "One of those documents states a method. Compare like with like and most of this disappears."

GL Biochem’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.