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TOF (mass spectrometer) Analyzer Question

  1. Nov 9, 2014 #1
    1. The problem statement, all variables and given/known data

    An unknown hydrocarbon ion required 9.415*10^-6 seconds to travel through the 0.250 T magnetic field of a mass spectrometer with a radius of curvature of 14.1 cm. Since the magnetic chamber is shaped like a 'D' it only travels half way around the circle.

    a. find the speed of the ion through the magnetic field
    b. identity of the ion using the charge to mass ratio (q/m)

    2. Relevant equations

    Fm = qvB

    Unknown variables: q (charge), m (mass), v (velocity) or V (voltage)

    3. The attempt at a solution

    a. Rearranging the formula gives me v=qBr/m. I do not have the (q/m) ratio, so that creates two unknown variables. Next, I tried substituting (4π^2/T^2) as an equivalent for qvB.

    The Fm is 4.453680806*10^11 N.

    After this step I am stuck.

    The velocity is 4.7*10^4 m/s, and the substance is pentane, with a (q/m) ratio of 1.34*10^6.
  2. jcsd
  3. Nov 9, 2014 #2


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    2017 Award

    Staff: Mentor

    You can calculate the curve length the ion travels in the spectrometer, and you know the time. That allows to get the speed.
    Afterwards you can find q/m.
  4. Nov 9, 2014 #3
    WOW THANKS. I didn't even know it was that simple!! thanks again! :)
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