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In a mass spectrometer the sample is vapourised, then ionised, then accelerated.

My textbook says that the high energy electrons from the electron gun knock electrons off the sample molecules and hence ionise the particles by 1+.

But do some particles get 2 or more electrons knocked out or is it always just one ?

I suppose once it has been ionised by 1+ it gets accelerated through the tube so it won't hang around for long but I would think that there is still a small window of time for further ionisations.

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    $\begingroup$ Don't forget that the abscissa in mass spectroscopy is $m/z$, i.e. the ratio of mass divided by charge. An example where double-charged ions play an important role, published as «open access» is «Identification of impurities in nafamostat mesylate using HPLC-IT-TOF/MS: A series of double-charged ions» by Zhang et al. in the Journal of Pharmaceutical Analysis 10 (2020) 346-350, doi.org/10.1016/j.jpha.2020.03.002. $\endgroup$
    – Buttonwood
    Commented Oct 10, 2020 at 20:07
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    $\begingroup$ @M.Farooq your comment would make an excellent answer... $\endgroup$
    – Curt F.
    Commented Apr 16, 2021 at 17:43
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    $\begingroup$ @CurtF., Changed it to an answer. $\endgroup$
    – ACR
    Commented Apr 16, 2021 at 17:56

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In electron impact, you would see mostly +1 charged ions. Electron impact is a "harsh" way of ionization. However, +1 charge is not a universal rule in MS. The state of ionization depends on the ionization source. Later in your courses you might encounter electrospray ionization. There you might have +14 charges, etc.

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    $\begingroup$ Your downvote will not change the facts! Sorry. $\endgroup$
    – ACR
    Commented Apr 16, 2021 at 18:23
  • $\begingroup$ Interesting , but in what sense is it ''harsh'' ? $\endgroup$
    – Kantura
    Commented Apr 16, 2021 at 20:50
  • $\begingroup$ EI is considered as a hard ionization technique because it breaks the molecule into many fragments. You rarely see the molecular ion-peak in an EI mass spectrum. $\endgroup$
    – ACR
    Commented Apr 16, 2021 at 22:04

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