Topic summary

Mass error in ppm: the arithmetic and the caveat — a second dataset

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

This is a generated summary. It shows the 5 most-liked posts from a topic of 25, 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.

o.nybergTL2 Moderator29 May 2026#4

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.

28 likes 2mo

ca.vermeulenTL2 Moderator Solution12 Jun 2026#8

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.

20 likes 2mo

f.chowdhuryTL2 Moderator4 Jul 2026#16

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.

27 likes 24d

r.serranoTL2 Moderator12 Jul 2026 · edited#19

Sample matrix effects: if a sample is dissolved in a complex matrix, other compounds in the matrix can suppress the peptide signal. Clean samples give higher sensitivity than dirty samples.

21 likes 16d

a.mwangiTL2 Moderator17 Jul 2026#21

z.vogel, post #6: I read post #4 twice before replying, because I had assumed the opposite. What mass accuracy establishes: the measured mass is consistent with a specific composition. What it does not establish: purity, sequence order, stereochemistry, or the absence of an isobaric species. Every one of those requires something else. Go to post

post #20 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.

26 likes in reply to #6 11d

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