Topic summary

Racemisation and why it is invisible to a mass measurement — what changed since

Analytics › Impurities & related substances forced degradation water content counter-ion content

This is a generated summary. It shows the 5 most-liked posts from a topic of 16, 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.

t.verhoevenTL21 Apr 2026#1

Racemisation and why it is invisible to a mass measurement — what changed since Writing it up because I had to work it out twice and would rather nobody else did.

What changes if the standard account of Racemisation is wrong? I ask because I have been treating it as settled and I noticed this week that I could not say why.

Working through the consequences rather than the evidence, since others here are better placed on the evidence.

60 likes 4mo

bias_varianceTL4Biostatistician13 Apr 2026#2

Relative response factors mean impurities are not detected in proportion to how much of them is present. A one per cent peak is not one per cent by mass unless the response factors happen to match.

Genuinely open to being wrong about this one.

17 likes 3mo

compounding_ruthTL4Pharmacist14 May 2026#6

Incomplete deprotection leaves a protecting group attached, raising the mass substantially and usually pushing retention much later. A late-eluting peak on a peptide chromatogram is worth asking about.

23 likes 2mo

j.sandvikTL23 Jun 2026#9

impurity_table, post #8: Fair, and the limits you put on it are the part I will remember. Go to post

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.

18 likes in reply to #8 2mo

buffer_reviewTL3Regular14 Jun 2026#11

I would put moderate confidence on the mainstream reading of Racemisation and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.

28 likes 1mo

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