Electric Sector Field Analyzer

Sector field analyzers are magnetic or electric sector fields or a combination of the two with ion focusing and separation properties used in static mass spectrometers. 

Besides a magnetic field, an electric sector field also influences the trajectory of the ions. An electric sector field analyzer as a section of the cylindrical condenser consists of two cylindrical... 

The alpha-particle instrument is shown in Fig. 1. The gas, supplied from a conventional gas handling system, is irradiated in the ionization chamber. The radiation is supplied from an enclosed polonium alpha source of a few hundred millicuries. The irradiated gas bleeds through a leak out of the ion source and into the evacuated electrode chamber. There, the ions effusing from the leak are captured by the electric fields while the gas is pumped away. The ions are focused, accelerated, and then subjected to mass analysis and electron multiplier detection in a 90° sector field analyzer tube. 

Magnetic sector field (B) Combination of magnetic (B) and electric sector fields (E) Quadrupole mass analyzer (Q) Time-of-flight mass analyzer (ToF)... 

Dynamic mass separation systems use the fact that ions with different masses (accelerated with the same voltage) possess several velocities and consequently their flight times are different. There are about 50 dynamic separation systems known2 using several types of ion movements (linear straight ahead, linear periodic or circular periodic as a function of the electric or magnetic sector field applied). The simplest dynamic mass separation system is a linear time-of-flight (ToF) mass analyzer, and a widely applied mass separation system is the quadrupole analyzer. 

Equation 4 is the cyclotron equation, coc corresponding to the cyclotron frequency (ICR frequency). The ICR frequencies are between a few kHz and several MHz. Equation 4 indicates that all ions with the same ratio of ion charge to ion mass possess the same ion cyclotron frequency. In contrast to other mass analyzers (magnetic/electric sector field, time-of-flight (TOF), quadrupol), the ion velocity has no direct influence on the relation between the measured value and the ion mass (ICR frequencies toc in equation 4 sector field radius of deflection r for magnetic selection in equation 5 TOF flight time t). 

If the ion kinehc energy changes due to dissociahon after acceleration, the electric sector can also be used as a mass analyzer. A scan of the sector field, E, separates the fragment ions based on their kinetic energies (Eq. 1.14),... 

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.

Sector mass analyzer A mass analyzer that uses either a magnetic field, or a combination of magnetic and electric fields, to change the direction of travel of high-kinetic energy ions. Ions of different masses are influenced to different degrees, providing the basis for a mass separation. 

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