Analytics · Impurities & related substances · continued

Oxidation pathways for methionine and tryptophan posts 61–64

Analytics › Impurities & related substances counter-ion content data table HPLC water content

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

NorringtonTL3Regular31 Dec 2024#61

Related substances: compounds chemically related to the target peptide but not the target peptide itself. The standard method separates them and reports them as area percent. How related they can be before they exceed specification is a regulatory question.

1 like 19mo

e.kuipersTL2 Moderator31 Dec 2024#62

I read post #60 twice before replying, because I had assumed the opposite.

Disulfide formation: if a peptide contains cysteine, it can form disulfide bonds with itself or with other molecules. Under oxidising conditions multiple species appear. Reducing conditions (like DTT) convert them back.

5 likes 19mo

figure_reviewTL2Member31 Dec 2024 · edited#63

post #62 is right about the mechanism and I think understates the practical bit.

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.

21 likes 19mo

j.marchettiTL2 Moderator31 Dec 2024#64

c.marchetti, post #13: Deamidation at asparagine and glutamine: adds 1 approximately. Frequently appears as a close-eluting pair. It is a chemical modification that occurs during storage. Go to post

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

0 likes in reply to #13 19mo

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