Same mass, different molecule: why identity by mass is not identity
An isoaspartate rearrangement changes the molecule and not the mass. A method that confirms identity by molecular weight alone will report it as the parent compound.
TheCompound Journal
Reporting on incretins, compounding & the peptide supply chain
The Supply Chain Dispatch
Reported from the analysis, not from a warning notice.
The health authority in Sweden has issued a warning on falsified exenatide injection pens found in the legitimate supply chain. The Journal has reviewed the notice and the accompanying photographs; the distinguishing features are a batch-number font difference and a needle-shield colour, neither of which a patient could reasonably be expected to detect.
Comparison of 15 certificates supplied by the reseller against the laboratory’s public archive matched 7 of them to reports commissioned by other parties, in some cases more than a year earlier. The reseller did not respond to two written requests for comment.
Comparison of 15 certificates supplied by the reseller against the laboratory’s public archive matched 7 of them to reports commissioned by other parties, in some cases more than a year earlier. The reseller did not respond to two written requests for comment.
The document is the weakest link in this trade. A certificate is a PDF; a laboratory letterhead is an image; a lot number is a string. Nothing in the ordinary transaction allows a buyer to confirm that a given report was issued for a given vial, and the four independent services differ in whether they offer any lookup at all.
Havel Novotný, independent laboratory quality manager, said the underfill finding was the more consequential one. "Nobody is being poisoned by a low content figure. Everybody using that vial is out by a fifth in every calculation they make."
Our series on identity confirmation covers the analytical detection of substitution in detail, including the mass differences that correspond to the commonest related compounds.
An isoaspartate rearrangement changes the molecule and not the mass. A method that confirms identity by molecular weight alone will report it as the parent compound.
Reported from the analysis, not from a warning notice.
The two ionisation techniques in general use produce different charge distributions, different adducts and different failure modes. Certificates almost never say which was…
A reminder that a purity figure is the output of a method, and that methods differ.
Documentation practice is the only part of vendor quality a buyer can assess before purchase.
The route did not close because of a rule about peptides.