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.
Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
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.
Two things before anyone answers the substance.
First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.
post #43 answers the question as asked. The question underneath it is different.
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.
This follows post #65 rather than contradicting it.
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.
Read the full topic (78 posts)
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2 | 293 | 3mo | |
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2 | 63 | 10mo | |
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+34 | 38 | 4.8k | 10mo |