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.nybergTL229 May 2026#4

A mass match establishes that the measured mass is consistent with the proposed composition. It does not establish purity, sequence order, or the absence of an isomer, and all three are frequently claimed from it.

Adding it because I spent an afternoon working it out and nobody should have to twice.

28 likes 2mo

ca.vermeulenTL2 Solution12 Jun 2026#8

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.

A guess, clearly labelled as one.

20 likes 2mo

f.chowdhuryTL24 Jul 2026#16

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.

27 likes 24d

r.serranoTL212 Jul 2026 · edited#19

Adducts — sodium and potassium especially — shift the observed mass in predictable increments. A report showing an unexplained plus twenty-two is usually showing you a sodium adduct.

Anyone who has looked at this more carefully, please correct the record.

21 likes 16d

a.mwangiTL217 Jul 2026#21

z.vogel, post #6: Nothing to add, except that this is the answer I would give if asked. Go to post

Fine by me. I had wanted a stronger conclusion and there is not one available.

26 likes in reply to #6 11d

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