Common adducts: sodium adds ≈22, potassium adds ≈38 compared to hydrogen. A [M+Na]+ peak is common and its mass is predictable from the base mass. One more caveat and then I will stop qualifying: the sample selected itself.
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.
Asking about Isotope patterns on behalf of the question I keep seeing asked badly, including by me.
Framed properly it is answerable. Framed the usual way it is not, and that is most of why the previous threads went nowhere.
Monoisotopic and average mass are different numbers and both appear on documents. At this molecular weight the difference is a few daltons, which is more than the tolerance being claimed.
I keep a log of this specifically because memory is unreliable about it.
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[2026 update] Charge states for a 4 kDa peptide, worked through
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+116 | 135 | 31k | 3mo |
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High-resolution MS on aggregates and what it can see — one year on
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+38 | 44 | 60k | 11mo |
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Charge states for a 4 kDa peptide, worked through — the long version
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2 | 293 | 3mo | |
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Coming back to: Deconvolution of a multiply charged envelope
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2 | 12k | 22mo |
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Oxidation pathways for methionine and tryptophan
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+58 | 63 | 1k | 19mo |
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Endotoxin and why it is a separate question from purity — what changed since
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+78 | 91 | 1k | 10h |
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Coming back to: Adsorption to container surfaces and to plastics
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2 | 459 | 17mo | |
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[2026 update] Charge states for a 4 kDa peptide, worked through
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…
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+116 | 135 | 31k | 3mo |
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Deletion sequences: expected mass shifts by residue — the long version
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+21 | 25 | 6.9k | 10h |