Electron volts , mass analyzers

An ion velocity of 72,294 m s appears rather high, but merely is 0.0024% of the speed of light. The acceleration voltages and thus, the ion velocities are the highest in TOF-MS, although magnetic sector instruments are operated with kilo-electron-volt ion beams, too (Chap. 4.3). The other types of mass analyzers require ions to enter at much lower kinetic energies. 

To couple a low-pressure MALDI source to a QIT, LQIT, or orbitrap mass analyzer, the primary concern other than having an efficient MALDI source is to be able to trap the gas-phase ions efficiently inside the analyzer. In the low-pressure MALDI experiment, ions can be formed inside the ion trap or they can be generated outside the device and injected into the analyzer. Ions are lifted by the matrix plume at a velocity of 500 m/s with several electron volts of energy and may undergo additional reactions in the plume. Once in the gas phase, the ions are accelerated as a result of either (a) an RF field in the case of internal ionization or (b) an external lens system for the external ion formation/injection scheme. Ions can be trapped efficiently in a QIT or LQIT if they have low kinetic energies (typically <20 eV), but the trap must be set to the appropriate RF trapping potentials and filled with helium buffer gas. In two similar configurations from 1993, the QIT was... 

The combination of electrospray ionization with magnetic sector mass spectrometers proved to be less technically challenging than the interfacing of MALDI. Electrospray ionization produces ions continuously, and thus it combines easily to scanning mass analyzers such as the magnetic sector. Thus, no modifications of the mass analyzer or detector are required for electrospray ionization. However, the ions produced by electrospray must be accelerated to kilo-electron-volt energies, and this requires some innovation with the design of the ion source. One solution is to float the entire electrospray source and... 

Mass spectral data shall be obtained using a low resolution instrument that utilizes 70 volts (nominal) electron energy in the electron impact mode. The system shall he capable of selected ion monitoring (SIM) for at least 18 ions per cycle, with a cycle time of 1 second or less. Minimum integration time for SIM is 25 milliseconds per m/z. The integration time used to analyze... 

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