Box 22-2 How Ions of Different Masses Are Separated by a Magnetic Field

Box 22-2 How Ions of Different Masses Are Separated by a Magnetic Field 

An ion with charge ze and velocity v traveling perpendicular to a magnetic field B experiences a force z.exB that is perpendicular to both the velocity vector and the magnetic field vector. This force deflects the ion through a circular path of radius r. The centripetal force (mx2/r) required to deflect the particle is provided by the magnetic field. 

Equating velocities from Equations A and B gives zeBr 

Equation C tells us the radius of curvature of the path traveled by an ion with mass m and charge z. The radius of curvature is fixed by the geometry of the hardware. Ions can be selected to reach the detector by adjusting the magnetic field, B, or the accelerating voltage, V. Normally, B is varied to select ions and V is fixed near 3 000 V. Transmission of ions and detector response both decrease when V is decreased. 

Kuebier. and H. Basch. Perttuoro Effects In Photoelectron Spectroscopy. J. Am. Chem. Soc. 1972,94,145. ] Here are other first ionization energies  

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