The one-quarter rule, and the paper that took it apart
Grading six widely repeated claims against the studies actually behind them.
Callum Brathwaite
Page 4 of 7 of this archive, newest first.
Archive — page 4
134 piecesWhat PeptideMeter can tell you about a vial by weighing its water
The physics of the drying cycle explains why some cakes are matte and full-volume and others are glassy discs, and why the difference is not cosmetic.
Janoshik result on a Guangzhou retatrutide lot lands 2.2 points below the supplier’s figure
The result is unremarkable. What the report omits is not.
Where the solvent front ends is a decision, not a fact
Regulated pharmaceutical practice has explicit reporting, identification and qualification thresholds. This trade has none, which is why a purity figure carries no…
The conservative convention: report the lower of two numbers
An orthogonal method separates on a different physical principle, so that species co-eluting in the first are likely to resolve in the second. Two runs of the same method at…
Medutest result on a Tianjin semaglutide lot lands 2.4 points below the supplier’s figure
The result is unremarkable. What the report omits is not.
The sample is not the batch
Chain of custody, in a regulated setting, begins at sampling. Here it begins when the package arrives.
Independent analysis puts a WWB semaglutide lot at 96.9%, against 93.3% on the certificate
The Journal submitted the sample and paid for the analysis. The vendor was told in advance.
Independent analysis puts a HJ exenatide lot at 98.4%, against 97.3% on the certificate
The report states the gradient, the wavelength and the integration threshold, which is more than most.
The 0.22 micron filter does the work, and it is the last line
Bioburden entering the filter, filter integrity, environmental monitoring and aseptic process simulation are the four pillars. The trade documents none of them.
A spectrum is a photograph of an ion, not of a molecule
The two ionisation techniques in general use produce different charge distributions, different adducts and different failure modes. Certificates almost never say which was…
Before anything is weighed, the peptide has to be charged
A brief and unromantic tour of the interface between a liquid sample and a vacuum.
Independent analysis puts a GGPeps tirzepatide lot at 96.6%, against 93.7% on the certificate
The result is unremarkable. What the report omits is not.
Bacteriostatic water, sterile water, and the 0.9 per cent that makes the difference
Every degradation pathway accelerates by orders of magnitude on reconstitution, because the solvent that lyophilisation removed is the reagent most of them need.
Reproducibility, measured rather than assumed
The Journal submitted split samples from single lots to three assay services, under names unconnected to this publication, and published each method alongside each result.
Everything on the page, in the order a chemist would read it
The purity figure is the least informative line on a well-constructed certificate and the only line most buyers read.
The question no chromatogram has ever answered
Every certificate circulating in this market answers a question about molecules. Almost none answers a question about organisms, pyrogens, or the integrity of the seal.
The arithmetic behind every identity confirmation, worked in full
A peptide has a monoisotopic mass and an average mass, they differ by several daltons at this molecular size, and a certificate that does not say which it quotes cannot be…
Independent analysis puts a SGN survodutide lot at 97.0%, against 92.8% on the certificate
A reminder that a purity figure is the output of a method, and that methods differ.
Freezing a reconstituted vial: the ice-water interface problem
An in-use period is established by a dedicated study on a specific formulation in a specific container at a specific concentration. Borrowing one from a marketed product is…