Electrostatic Analyzer Electric Sector

E= electric potential (voltage) between the inner and outer ESA plates R = radius of curvature of the ion trajectory 

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The electrostatic sector or electrostatic analyzer (ESA) produces a radial electric field between two oppositely charged plates extending over the ESA angle ( ) (Fig. 4.21). An ion passes the ESA midway on a circular path if... 

However, ions in a radial electrostatic held also follow a circular trajectory. The electrostatic held is an electric sector and separates ions by kinetic energy, not by mass (Fig. 9.17). The ion beam from the source can be made much more homogeneous with respect to velocities of the ions if the beam is passed through an electric sector before being sent to the mass analyzer. The electric sector acts as an energy hlter only ions with a very narrow kinetic energy distribuhon will pass through. 

Resolution traduces the ability of an analyzer to separate ions it correlates with the precision of the measure of m/z ratios. The analyzers are generally separated into two categories low and high resolution. The first category groups quadrupoles and ion traps, the second includes ICR, TOP analyzers equipped with electrostatic reflectors, and devices that combine a magnetic sector with an electric sector. 

If one wishes to carry ont gas-phase experiments, that is, to manipulate mass-selected ions inside the mass spectrometer, ion-trap analyzers offer the broadest arsenal of experiments including unimolecular fragmentations as well as bimolecular reactions with sufficiently volatile neutral reagents. Consequently, the choice of analyzer is also an important point. Mass analyzers use static or dynamic electric or magnetic fields to separate the ions either in time or in space. Sector-field mass analyzers use magnetic (B) and electrostatic (E) sectors to separate the ions... 

Magnetic sector and electrostatic sector mass analyzers are well suited for operation with continuous ion sources the trajectories of moving ions are curved by forces developed by the electric or magnetic fields (Fig. 2.9). The extent of this curvature depends on an ion s m/z. Sector analyzers can be used to monitor a single ion with high resolution. A narrow slit is installed between the detector and the ion analyzer the position of the slit determines... 

Fig. 2.9. General schematic of a sector mass analyzer. Ions extracted from the ion source are accelerated by an electrostatic field (accelerating potential, 10 and enter the sector analyzer with velocity, v. Electric (electric flux density, E) or magnetic (magnetic flux density, 6) fields bend the trajectory of the ions into curved paths with radius, r. Trajectories of ions with larger m/z are affected more than smaller ones. An illustration of the direction-focusing ion beam approach in a magnetic sector mass analyzer is shown in the insert. Due to the dependence of the radius of an ion s trajectory on its kinetic energy ( ) in the electrostatic sector mass analyzer and on its momentum (mv) in the magnetic sector mass analyzer, the systems are also referred to as ion energy and ion momentum filters.

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