EB or BE geometry mass analysers

However, since the velocities of ions before acceleration are non-zero, their total kinetic energy must take account of their initial kinetic energy, Eq, which is small and unknown  

Only the ions which have followed the trajectory with radius R within the flight tube imposed by the instrument will be detected. Hence, to obtain a spectrum within a given mass range, the intensity of the field B has to be progressively modified. All ions, whatever the miz value, will successively follow, one after the other, the unique trajectory leading to the detector. Such a scan requires around 

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