A mass spectrometer is a device that separates ions by mass, by shooting them at

Question

A mass spectrometer is a device that separates ions by mass, by shooting them at a known initial speed into a magnetic field. I have a hand-me-down mass spec that is designed to separate three isotopes of singly ionized carbon ions. It has a port where the unsorted ions enter the field, and three collectors positioned as shown. Which collector is for the^12C ions (mass 12 amu), which for the^13C ions (13 amu), and which for the^14C ions? I am going to shoot positively charged ions into the mass spec. In what direction should the magnetic field point? My velocity selector only passes ions with a speed of 8.0 Times 10^5 m/s. How strong a magnetic field do I need for the mass spec? If the velocity selector is not precise enough, ions can wind up in the wrong collector. By what percentage would a^13C ion's speed need to be off in order for it to end up in the^14C collector, and would it have to be that much too high or too low? What would happen to a negatively charged ion? Why aren't the three collectors lined up at the same height?

Explanation / Answer

a)

r = mv/qB

since v , q and B are same all three particles , the value of mass of each particle decides the radius of path

greater the mass , greater is the radius

C-14 will have the greatest radius 0.350 m and will be detected by the righmost deterctor

C-13 will have the greatest radius 0.325 m and will be detected by the central detector

C-12 will have the smallest radius 0.300 m and will be detected by the first detector

b)

the direction of magnetic field must be inward to the page so that the particles are forced towards the up direction toward detectors.

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