Kinetic energy, magnetic sector

Magnetic sector instruments typically operate with ion sources held at a potential of between 6 and 10 kV. This results in ions with keV translational kinetic energies. The ion kinetic energy can be written as zt V = Ifur and thus the ion velocity is given by the relationship... 

Ions accelerated out of the ion source with keV translational kinetic energies (and m/z selected with the magnetic sector) will arrive in the FFR of the instrument in several microseconds. Ions dissociating on this... 

To be effective, it is necessary for the ions traversing the instniment to experience several RF cycles. Thus, unlike magnetic sector instmments, the ions fonned in the ion source of a quadnipole mass filter apparatus are accelerated to only a few eV kinetic energy (typically 5-10 eV). The timescale of the experiment is therefore... 

Magnetic sector mass spectrometers accelerate ions to more than 100 times the kinetic energy of ions analysed in quadrupole and ion trap mass spectrometers. The higher accelerating voltage contributes to the fact that ion source contamination is less likely to result in degraded sensitivity. This is particularly important for analysis that requires stable quantitative accuracy. 

Fig. 4.18. Direction focusing properties of a 180° magnetic sector on a diverging beam of ions of the same m/z and the same kinetic energy and effect on ions of different m/z- In this illustration, B has to come out of the plane towards the reader for positive ions.

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