What a split-sample exercise can establish, and what it cannot
Two years ago we ran an anonymised version of this comparison and promised a named one. This is it, with every method printed in full.
Independent testing
Page 18 of 27 of this archive, newest first.
Independent analysis puts a BCH mazdutide lot at 95.5%, against 94.0% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
The question no chromatogram has ever answered
Purity, content, identity, sterility and endotoxin are five separate determinations. A single sheet of paper carrying one of them is not evidence about the other four.
Independent analysis puts a SGN mazdutide lot at 99.2%, against 96.3% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Medutest result on a Xi'an tirzepatide lot lands 2.1 points below the supplier’s figure
The Journal submitted the sample and paid for the analysis. The vendor was told in advance.
Check the vial, not the box
The interval between manufacture and analysis is the most under-read figure on the page, and the one most likely to matter by the time a vial is opened.
VendorInvestigate result on a Guangzhou retatrutide lot lands 3.9 points below the supplier’s figure
The result is unremarkable. What the report omits is not.
The reviewer, the approver, and why regulated documents carry two names
What the Journal asks when a document arrives unsigned, and what the answers have been.
VendorInvestigate result on a Nantong cagrilintide lot lands 4.4 points below the supplier’s figure
The report states the gradient, the wavelength and the integration threshold, which is more than most.
The conservative convention: report the lower of two numbers
Aggregates dissociate in the mobile phase and are recorded as monomer. Only a size-based separation reports them.
Independent analysis puts a Homopeptide tirzepatide lot at 99.3%, against 95.3% on the certificate
The result is unremarkable. What the report omits is not.
Who chose the vial that was tested?
Every third-party report in this market describes a sample somebody chose to send. That choice is outside the laboratory’s control and outside its records.
Independent analysis puts a SGN exenatide lot at 96.4%, against 94.7% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
How far back does this document actually reach?
A document is only as good as the chain that connects it to the material, and most chains here are two or three links longer than the paperwork admits.
Repackaging, subdivision, and the batch number that changed hands
A document is only as good as the chain that connects it to the material, and most chains here are two or three links longer than the paperwork admits.
Independent analysis puts a QST dulaglutide lot at 95.3%, against 91.7% on the certificate
The result is unremarkable. What the report omits is not.
What a laboratory knows about the material it receives
What a laboratory can and cannot know about the provenance, storage history and representativeness of what lands on its bench.
What a mass spectrometer does to a peptide before it measures anything
A brief and unromantic tour of the interface between a liquid sample and a vacuum.
Independent analysis puts a TFC dulaglutide lot at 95.8%, against 95.1% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Independent analysis puts a ERP survodutide lot at 95.6%, against 92.3% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.