Desalting before analysis: some samples need desalting to remove salts that suppress the peptide signal. Report whether desalting was used, because it can affect the apparent ionization efficiency and the reported purity.
Topic summary
Charge states for a 4 kDa peptide, worked through
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.
c.correia, post #20: post #19 answers the question as asked. The question underneath it is different. 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… Go to post
Coming back to post #62, because the follow-up matters more than the original answer.
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.
cannula_trace, post #21: 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. Go to post
This follows post #69 rather than contradicting it.
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.
This follows post #82 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.
29 likes 17mo
careful_beginner, post #72: This follows post #69 rather than contradicting it. 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. Go to post
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.
This follows post #132 rather than contradicting it.
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.
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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