Tandem mass spectrometry, and the difference between weighing and reading
The Journal’s standing position: a mass that matches is necessary evidence of identity and nowhere near sufficient.
Félix Oyarzún
Page 3 of 7 of this archive, newest first.
Archive — page 3
134 piecesThe badge is about a sample. The listing is about a product.
The Journal does not treat a badge as evidence and states so wherever it reports one.
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.
A vial can be 99.4 per cent pure and not sterile in the same afternoon
The Journal has read several hundred certificates from twenty companies. We set out what the documents actually cover, and what a reader is filling in from imagination.
What Medutest charges to answer the pyrogen question
The masking phenomenon known as low endotoxin recovery means a formulation can return a clean result while containing endotoxin the assay cannot see.
The badge economy, and what it is actually certifying
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.
The cake tells you something, and it is not purity
Multiple-dose vials are designed for a defined number of punctures. Nobody counts, and the elastomer does not care whether anybody counts.
Same material, different gradients, different answers
Duplicate submissions under different names test within-laboratory repeatability, which is a different quantity from between-laboratory reproducibility.
The shelf life ends when the diluent goes in
At low concentrations a measurable fraction of peptide can adsorb to glass and plastic surfaces, and the loss is largest exactly where it is least expected.
Independent analysis puts a SSA dulaglutide lot at 96.0%, against 95.0% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.
Independent analysis puts a GL Biochem exenatide lot at 96.5%, against 93.6% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
Six lines that would make an identity statement checkable
What the Journal asks for when it writes to a supplier about an identity claim, and how often it gets it.
What column temperature does to selectivity
A shallow gradient resolves impurities that a steep one runs into the parent peak. Both methods are legitimate; only one of them can see the small stuff.
The out-of-range flag is a statistical convention with a printer attached
A twelve-analyte panel in a perfectly healthy person has roughly even odds of producing at least one flagged result.
What a diode array adds, and why the certificate never shows it
A diode-array detector records the whole spectrum at every time point and can confirm that a peak is spectrally homogeneous. Almost nobody prints that information.
One method is one opinion
Where two methods disagree, the conservative convention is to report the lower figure. It is not universal, and whether a laboratory follows it belongs on the report.
VendorInvestigate result on a Shenzhen semaglutide lot lands 1.1 points below the supplier’s figure
The result is unremarkable. What the report omits is not.
Why a dry powder is a chemical reactor with the volume turned down
Residual moisture is measured routinely in regulated manufacture, is reported almost nowhere in this trade, and predicts long-term stability better than any other single…
Independent analysis puts a GGPeps liraglutide lot at 97.8%, against 93.8% on the certificate
The Journal submitted the sample and paid for the analysis. The vendor was told in advance.
Independent analysis puts a MKM dulaglutide lot at 99.2%, against 96.7% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.