Accuracy, precision and the tolerance nobody states
Parts per million sound impressive until they are converted into daltons at the molecular weight of the thing being measured.
Independent testing
The four services this market relies on, examined as institutions.
The named comparison we promised two years ago
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.
Set the threshold at a tenth of a per cent and the small impurities vanish
We work through a single chromatogram twice, under two integration conventions, and show where the difference comes from.
Same material, different gradients, different answers
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
Independent analysis puts a TFC tirzepatide lot at 98.3%, against 95.4% on the certificate
The result is unremarkable. What the report omits is not.
Janoshik result on a Qingdao semaglutide lot lands 3.7 points below the supplier’s figure
A reminder that a purity figure is the output of a method, and that methods differ.
Independent analysis puts a FGP exenatide lot at 95.7%, against 94.1% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
One method is one opinion
Aggregates dissociate in the mobile phase and are recorded as monomer. Only a size-based separation reports them.
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.
VendorInvestigate result on a Chengdu retatrutide lot lands 3.0 points below the supplier’s figure
A reminder that a purity figure is the output of a method, and that methods differ.
Who signed this, and what did they undertake by signing it
Somebody has to be answerable for a release document. On most certificates in this market, nobody is named at all.
Independent analysis puts a ERP cagrilintide lot at 98.8%, against 97.3% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
PeptideMeter result on a Xianning semaglutide lot lands 4.4 points below the supplier’s figure
The supplier has not disputed the finding. It has not explained the gap either.
Disregard limits: what a regulated laboratory does with a tiny peak
Baseline placement under a tailing peak is a judgement call with a direct effect on the area. It is one of the few places where two competent analysts genuinely disagree.
How a claim degrades between the bench and the listing
A badge asserts that something was tested. It does not assert what, when, on whose sample, by what method, or whether the lot on sale is the lot that was tested.
Independent analysis puts a Homopeptide semaglutide lot at 96.0%, against 92.4% on the certificate
The result is unremarkable. What the report omits is not.
Independent analysis puts a QYB mazdutide lot at 95.3%, against 92.9% on the certificate
The result is unremarkable. What the report omits is not.
The word “confirmed” is doing an enormous amount of work on this certificate
The Journal’s standing position: a mass that matches is necessary evidence of identity and nowhere near sufficient.
The specification sheet says 500,000. The report says conforms.
Every instrument specification quoted in an advertisement is a best case obtained on a calibration mixture, not on a submitted vial.
PeptideMeter result on a Wuxi dulaglutide lot lands 2.2 points below the supplier’s figure
The report states the gradient, the wavelength and the integration threshold, which is more than most.