Topic summary

MS/MS sequence confirmation: what it costs and when it is worth it — what changed since

Analytics › Mass spectrometry charge states LC-MS MALDI-TOF counter-ion content Closed

This is a generated summary. It shows the 6 most-liked posts from a topic of 40, 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.

i.amankwahTL22 Apr 2026#14

g.oyelaran, post #9: What mass accuracy establishes: the measured mass is consistent with a specific composition. What it does not establish: purity, sequence order, stereochemistry, or the absence of an isobaric species. Every one of those requires something else. Go to post

Tandem mass spectrometry: MS/MS fragments the molecular ion and uses fragment masses to confirm identity and detect modifications. A simple identity confirmation by LC-MS does not address post-translational modifications or impurities with the same or very close mass.

22 likes in reply to #9 4mo

vial_deskTL3Regular12 Apr 2026#17

I had written a reply contradicting post #13 and deleted it. Here is what survived.

Positional isomers and epimers are mass-identical. Any argument that a mass result rules them out is wrong, and it is the commonest overclaim in this subcategory.

That is one dataset and I would not build a rule on it.

31 likes 4mo

a.adebayoTL22 May 2026 · edited#23

vial_desk, post #17: I had written a reply contradicting post #13 and deleted it. Here is what survived. Positional isomers and epimers are mass-identical. Any argument that a mass result rules them out is wrong, and it is the commonest overclaim in this subcategory. That is one dataset and I would not build a rule on it. Go to post

Positional isomers and epimers are mass-identical. Any argument that a mass result rules them out is wrong, and it is the commonest overclaim in this subcategory.

32 likes in reply to #17 3mo

c.silvaTL214 May 2026#27

24 likes 2mo

a.jansenTL223 May 2026#30

On post #28 — agreed on the reasoning, with one qualification.

Resolution: "high resolution" commonly means <5 ppm across the mass range. Unit-resolution instruments achieve ±1 Da at best and cannot distinguish two species differing by less than 1 Da in total mass.

Scoping that to what I have actually seen rather than what I have read.

23 likes 2mo

CFairweatherTL1Member12 Jun 2026#37

I had written a reply contradicting post #35 and deleted it. Here is what survived.

22 likes 2mo

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MS/MS sequence confirmation: what it costs and when it is worth itAnalytics › Mass spectrometry · 6 replies

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