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    I'm quite confused about this concept (which I'm probably being stupid about... but here goes):

    Mass spectrometry turns atoms into positive ions, atoms are vaporised to form gas particles, then ionised by removing an electron (to form an ion), accelerated, deflected and then detected - which I understand. Yet, a mass spectrometer gives information of the relative isotopic mass and abundance?

    I thought that isotopes were atoms of the same element with the same relative atomic mass but different mass numbers (numbers of neutrons)? So the atom forms an ion by removing an electron, but for it to become an isotope then surely something should happen to the neutrons in the atom?

    Once again, I'm sure that I'm being stupid here but can anyone shed some light on my misunderstanding brain?
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    it does not create isotopes, it detects them

    sample (sometimes a mixture of isotopes) ---> becomes vaporised + ionised + accelerated + deflected ----> different masses are detected (including isotopes)
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    (Original post by Farseer)
    it does not create isotopes, it detects them

    sample (sometimes a mixture of isotopes) ---> becomes vaporised + ionised + accelerated + deflected ----> different masses are detected (including isotopes)
    Ah! That makes sense... jeeze I knew that I missed something!

    So if you were to put something that was pure carbon (no other elements) and you used a mass spectrometer you would get different masses, which could be forms of both isotopes (carbon 11 and carbon 13) and the non-isotope (carbon 12)?
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    (Original post by Sulfur)
    Ah! That makes sense... jeeze I knew that I missed something!

    So if you were to put something that was pure carbon (no other elements) and you used a mass spectrometer you would get different masses, which could be forms of both isotopes (carbon 11 and carbon 13) and the non-isotope (carbon 12)?
    carbon has three natural isotopes: 12, 13 and 14

    it's almost all carbon 12
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    (Original post by Sulfur)
    I thought that isotopes were atoms of the same element with the same relative atomic mass but different mass numbers
    This might be part of your problem, but they have the same atomic (proton) number, but different mass number. I think not, though. I just thought I'd point out your mistake.

    If you had a mole of (for example) carbon, in the form of diamond (approx. 12 g) and fed it into a mass spec machine, you will be feeding in 6.02 x10 23 atoms. Of that vast number of atoms, most will have six neutrons (i.e. C-12), but some atoms will have seven or eight (i.e. C-13 or C-14).

    When they are atomised, ionised, accelerated and deflected, some most will be deflected and be detected as C-12 atoms, but a small proportion (1.1%-ish) will be C-13 and a smaller proportion C-14.

    If you fed in a pure C-12 sample, then all of the signal detected would have an m/z value of 12.
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    (Original post by Pigster)
    This might be part of your problem, but they have the same atomic (proton) number, but different mass number. I think not, though. I just thought I'd point out your mistake.

    If you had a mole of (for example) carbon, in the form of diamond (approx. 12 g) and fed it into a mass spec machine, you will be feeding in 6.02 x10 23 atoms. Of that vast number of atoms, most will have six neutrons (i.e. C-12), but some atoms will have seven or eight (i.e. C-13 or C-14).

    When they are atomised, ionised, accelerated and deflected, some most will be deflected and be detected as C-12 atoms, but a small proportion (1.1%-ish) will be C-13 and a smaller proportion C-14.

    If you fed in a pure C-12 sample, then all of the signal detected would have an m/z value of 12.
    Thank you very much - yup I think that I understand it now.

    I originally thought that a sample (e.g made of carbon only) had no isotopes in it, so it was pure C-12 and hence when it went through mass spectrometry, it became an isotope. But in actuality, mass spectrometry just determines and finds out the ABUNDANCE of the isotopes/non-isotopes that were already in the sample, and the mass of each ion in the sample too - so mass spectrometry doesn't form isotopes as I thought previously, it just measures the quantity and masses of them already present in a sample.
 
 
 
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