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.
For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.
Coming back to post #11, because the follow-up matters more than the original answer.
Mass accuracy is expressed in parts per million. It is the difference between observed and theoretical mass divided by theoretical mass, multiplied by a million. A high-resolution instrument in good calibration achieves low single-digit ppm on a peptide of this size.
post #37 is right about the mechanism and I think understates the practical bit.
Mass accuracy is expressed in parts per million. It is the difference between observed and theoretical mass divided by theoretical mass, multiplied by a million. A high-resolution instrument in good calibration achieves low single-digit ppm on a peptide of this size.
Electrospray ionisation produces multiply charged ions. For a 4 kDa peptide you expect mostly 2+, 3+, and 4+ charge states. Reading an electrospray spectrum means recognizing the envelope, not looking for one peak.
I disagree with the reply above, and I think the disagreement is substantive rather than terminological.
The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.
post #86 is right about the mechanism and I think understates the practical bit.
Mass accuracy is expressed in parts per million. It is the difference between observed and theoretical mass divided by theoretical mass, multiplied by a million. A high-resolution instrument in good calibration achieves low single-digit ppm on a peptide of this size.
Picking up post #91: that is the part I would want checked first.
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.
Electrospray ionisation produces multiply charged ions. For a 4 kDa peptide you expect mostly 2+, 3+, and 4+ charge states. Reading an electrospray spectrum means recognizing the envelope, not looking for one peak.
Read the full topic (109 posts)
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Reading an MS report that only gives you a single number
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+100 | 113 | 48k | 13mo |
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+70 | 77 | 3.5k | 15mo |
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What a 2 ppm match establishes, and what it does not
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+56 | 60 | 5.2k | 9mo |
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Second pass at: What a 2 ppm match establishes, and what it does not
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+44 | 49 | 8.1k | 1d |
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+2 | 6 | 2.7k | 1d |
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Coming back to: Deconvolution of a multiply charged envelope
On the subject in the title: Deconvolution of a multiply charged envelope Working notes rather than a conclusion. Working through the identity arithmetic and I would like it checked. tirzepatide has a…
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2 | 12k | 22mo | |
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Mass error in ppm: the arithmetic and the caveat
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+108 | 125 | 1.5k | 5mo |
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Charge states for a 4 kDa peptide, worked through
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+124 | 146 | 15k | 16mo |
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Impurity thresholds: where the common numbers come from — what changed since
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2 | 61k | 3mo | |
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Endotoxin and why it is a separate question from purity
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2 | 22k | 4mo |