Topic summary

Charge states for a 4 kDa peptide, worked through

Analytics › Mass spectrometry high-resolution MS counter-ion content charge states LC-MS mass error (ppm) Solved

This is a generated summary. It shows the 9 most-liked posts from a topic of 147, 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.

r.mensahTL2 Solution2 Mar 2025#8

Where I would push back on the charge states consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.

27 likes 17mo

z.vogelTL26 Mar 2025#37

Trifluoroacetate adducts are common in material purified with TFA and are one reason a mass spectrum from a peptide can look busier than expected.

Correct me on the arithmetic if it is wrong; I would rather know.

32 likes 17mo

v.okonkwoTL27 Mar 2025#43

Charge states is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.

30 likes 17mo

e.ndiayeTL210 Mar 2025 · edited#64

c.correia, post #20: Building on post #19 rather than restating it. 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. Go to post

Coming back to post #62, because the follow-up matters more than the original answer.

Charge states is worth one more sentence than it usually gets, and the sentence is the one about how the number was arrived at.

31 likes in reply to #20 17mo

careful_beginnerTL1Member11 Mar 2025 · edited#72

cannula_trace, post #21: 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

Building on post #69 rather than restating it.

An acylated peptide has a mass that reflects the modification, so comparing against the mass of the unmodified backbone gives a mismatch that is not an error.

On reflection I would soften that slightly.

30 likes in reply to #21 17mo

g.ekstromTL211 Mar 2025#79

The reason charge states keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.

31 likes 17mo

e.ndiayeTL212 Mar 2025#85

Adding a note of thanks rather than an opinion. I did not know most of that.

29 likes 17mo

c.nybergTL214 Mar 2025#106

careful_beginner, post #72: Building on post #69 rather than restating it. An acylated peptide has a mass that reflects the modification, so comparing against the mass of the unmodified backbone gives a mismatch that is not an error. On reflection I would soften that slightly. Go to post

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.

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

32 likes in reply to #72 16mo

sterile_tableTL3Regular17 Mar 2025#135

Right, and stated more narrowly than I would have dared to state it.

29 likes 16mo

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Distinguishing a deletion sequence by mass alone — the long versionAnalytics › Mass spectrometry · 44 replies

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