Topic summary

A rising related-substance total over six months: degradation or method drift?

Analytics › Impurities & related substances data table endotoxin testing HPLC Closed

This is a generated summary. It shows the 6 most-liked posts from a topic of 43, in their original order, with the accepted answer included where one exists. It is a reading aid and it will miss nuance — the full topic is the record.

aliquot_lineTL3Regular25 Aug 2024#8

Racemisation produces a diastereomer that is mass-identical and chromatographically resolvable only on a method chosen for the purpose. Standard reversed-phase frequently will not separate it.

The short answer was in the first line; everything after is the working.

26 likes 23mo

v.fontaineTL21 Sep 2024#24

I had written a reply contradicting post #22 and deleted it. Here is what survived.

Oxidation at methionine and tryptophan: adds 16 per oxygen. Usually elutes earlier. Oxidation is common in storage, especially if the solution is exposed to light or if antioxidants are not present.

Happy to expand any of that if it is the useful part.

33 likes 23mo

l.trevinoTL22 Sep 2024#28

Understood. Thank you for being specific about the limits of it.

25 likes 23mo

steady_stateTL3Regular4 Sep 2024#32

aliquot_line, post #8: Racemisation produces a diastereomer that is mass-identical and chromatographically resolvable only on a method chosen for the purpose. Standard reversed-phase frequently will not separate it. The short answer was in the first line; everything after is the working. Go to post

Taking post #29 at face value and following it one step further.

Deamidation at asparagine and glutamine: adds 1 approximately. Frequently appears as a close-eluting pair. It is a chemical modification that occurs during storage.

Nothing above should be read as advice about what anyone else should do.

31 likes in reply to #8 23mo

dietitian_hollisTL3Dietitian5 Sep 2024#36

c.vermeulen, post #12: Off-target structures: if the sequence synthesis goes wrong, a completely different amino acid can be incorporated. The resulting off-target peptide is a structural isomer with the same mass but a different sequence. No chromatographic purity method detects this without a reference standard. Go to post

Building on post #33 rather than restating it.

Residual solvents: traces of solvents used in purification. These are usually tested by gas chromatography, not by HPLC. A specification for residual solvents should be stated separately from the purity.

I am confident about the direction and much less about the magnitude.

23 likes in reply to #12 23mo

dr_bhattacharyaTL3Physician7 Sep 2024#43

A supplier that can tell you what its principal impurity is has answered a harder question than one that can tell you its purity, and the answer is more useful.

I am aware this is the third time this month I have made this point.

28 likes 23mo

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Promoted into the documentation commons. The content of this topic is maintained at Bacterial endotoxin testing, with named maintainers and a review date. The promotion was discussed in doc review. Corrections are best raised against the document, which is the version that gets kept current.

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