Topic summary

Coming back to: Oxidation and deamidation mass shifts, tabulated

Analytics › Mass spectrometry LC-MS charge states MALDI-TOF high-resolution MS mass error (ppm)

This is a generated summary. It shows the 6 most-liked posts from a topic of 39, 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.

h.ferrariTL2 Moderator28 Mar 2025#1

Oxidation and deamidation mass shifts, tabulated — setting out what I have, and where I think it stops being reliable.

Working through the identity arithmetic and I would like it checked.

retatrutide has a monoisotopic mass close to 4731.3 Da. On an electrospray instrument I would expect to see the multiply charged series rather than the intact singly charged ion, so for the doubly charged species I calculate (4731.3 + 2 x 1.00728) / 2, and for the triply charged the analogous expression.

The observed values in the report sit within a few ppm of those. My question is what that actually establishes, because I have seen people treat a mass match as a purity result and I do not think it is one.

36 likes 16mo

y.adeyemiTL2 Moderator31 May 2025#11

h.ferrari, post #1: Oxidation and deamidation mass shifts, tabulated — setting out what I have, and where I think it stops being reliable. Working through the identity arithmetic and I would like it checked. retatrutide has a monoisotopic mass close to 4731.3 Da. On an electrospray instrument I would expect to see the multiply charged series rather than… Go to post

Picking up post #8: that is the part I would want checked first.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

24 likes in reply to #1 14mo

two_year_lineTL3Regular24 Jun 2025#16

a.norgaard, post #6: This follows post #3 rather than contradicting it. Charge states observed: for semaglutide (4113.6 Da) the doubly charged ion appears at m/z ≈ 2057, triply charged at ≈ 1371, quadruply at ≈ 1029. Those are the positions to look for; the heights depend on the ionization efficiency. Go to post

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

33 likes in reply to #6 13mo

bias_varianceTL4Biostatistician12 Jul 2025#20

t.marchetti, post #10: 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. Go to post

Coming back to post #18, because the follow-up matters more than the original answer.

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.

25 likes in reply to #10 13mo

n.silvaTL2 Moderator2 Aug 2025#25

Calibration matters: a high-resolution instrument out of calibration can report mass with ppm error large enough to be uninformative. Check when the instrument was last calibrated before trusting the reported accuracy.

29 likes 12mo

IbrahimoviTL2Member26 Aug 2025#31

post #30 is right about the mechanism and I think understates the practical bit.

31 likes 11mo

Read the full topic (39 posts)

This topic was referenced in

[2026 update] Why mass spectrometry cannot tell you about an epimerAnalytics › Mass spectrometry · 2 replies

Suggested topics

Topic	Participants	Replies	Views	Activity
About the Mass spectrometry category Analytics › Mass spectrometry LC-MS high-resolution MS mass error (ppm) Pinned Wiki LC-MS and high-resolution MS, charge states, mass accuracy in ppm, and what identity confirmation does and does not establish. This post is a community wiki: any member at trust level 3 or above can edit it,…	+5	9	19k	6h
Distinguishing a deletion sequence by mass alone — the long version Analytics › Mass spectrometry high-resolution MS mass error (ppm) charge states MALDI-TOF On the subject in the title: Distinguishing a deletion sequence by mass alone — the long version Working notes rather than a conclusion. I would like to understand what this number means before I repeat it…	+38	44	60k	11mo
Second pass at: Counter-ion content and its effect on measured mass Analytics › Mass spectrometry mass error (ppm) counter-ion content MALDI-TOF charge states Solved Second pass at: Counter-ion content and its effect on measured mass Writing it up because I had to work it out twice and would rather nobody else did. Working through the identity arithmetic and I would like…		4	16k	4mo
Distinguishing a deletion sequence by mass alone Analytics › Mass spectrometry mass error (ppm) high-resolution MS LC-MS MALDI-TOF Solved Distinguishing a deletion sequence by mass alone Writing it up because I had to work it out twice and would rather nobody else did. Working through the identity arithmetic and I would like it checked.…	+121	129	25k	17mo
[2026 update] Charge states for a 4 kDa peptide, worked through Analytics › Mass spectrometry counter-ion content MALDI-TOF high-resolution MS LC-MS On the subject in the title: Charge states for a 4 kDa peptide, worked through Working notes rather than a conclusion. Working through the identity arithmetic and I would like it checked. semaglutide has a…	+116	135	31k	3mo

Related topics — sharing the tags LC-MS, charge states, MALDI-TOF

Topic	Participants	Replies	Views	Activity
Oxidation and deamidation mass shifts, tabulated Analytics › Mass spectrometry counter-ion content charge states LC-MS mass error (ppm) Solved Posting this under the heading it deserves: Oxidation and deamidation mass shifts, tabulated Everything below is what sits behind that. Working through the identity arithmetic and I would like it checked.…	+67	76	21k	16mo
Second pass at: Where impurities in solid-phase peptide synthesis come from Analytics › Impurities & related substances counter-ion content data table endotoxin testing HPLC Closed Posting this under the heading it deserves: Second pass at: Where impurities in solid-phase peptide synthesis come from Everything below is what sits behind that. A documentation question rather than an…	+47	51	3.3k	5mo
Residual solvents and scavengers: what is looked for Analytics › Impurities & related substances counter-ion content HPLC data table forced degradation Solved On the subject in the title: Residual solvents and scavengers: what is looked for Working notes rather than a conclusion. Posting the method first, because I know what the first three replies will otherwise…	+19	23	39k	14mo
Particulates in a reconstituted solution: identifying the likely source Analytics › Impurities & related substances counter-ion content data table HPLC water content Posting this under the heading it deserves: Particulates in a reconstituted solution: identifying the likely source Everything below is what sits behind that. Posting the method first, because I know what the…	+15	19	13k	9mo
Isotope patterns and why the monoisotopic peak is not the tallest — does this still hold? Analytics › Mass spectrometry charge states counter-ion content high-resolution MS mass error (ppm) Solved Isotope patterns and why the monoisotopic peak is not the tallest — does this still hold? — that is the question, and I have not found it answered plainly anywhere I have looked. Working through the identity…		2	4.6k	7h