Analytics · Mass spectrometry

Deconvolution of a multiply charged envelope

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

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integrator_draftTL3Regular14 Feb 2025#1

Deconvolution of a multiply charged envelope — setting out what I have, and where I think it stops being reliable.

Working through the identity arithmetic and I would like it checked.

tirzepatide has a monoisotopic mass close to 4813.5 Da. On an electrospray instrument I would expect to see the multiply charged series rather than the intact singly charged ion, so for the doubly charged species I calculate (4813.5 + 2 x 1.00728) / 2, and for the triply charged the analogous expression.

The observed values in the report sit within a few ppm of those. My question is what that actually establishes, because I have seen people treat a mass match as a purity result and I do not think it is one.

20 likes 17mo

i.amankwahTL2 Moderator27 Jun 2025#2

Purity and identity are different questions: LC-MS establishes that the species at a retention time has the expected mass. It does not establish how much of the sample is that species (that is what LC-UV purity answers).

3 likes 13mo

j.vandermolenTL3Regular30 Sep 2025#3

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.

0 likes 10mo

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