Electrostatic quadrupole focuser

Figure 4. The electrostatic quadrupole triplet lens and target chamber used for micro PIXE showing the 30 sq mm Si(Li) X-ray detector and the absotber ladder at 135 the RBS detectors which are at 158 above and below the lens the Ge(Li) PIGE detector and collimator the electron flood gun and the movable zoom microscope used for focusing and alignment of the beam.

For polar molecules with an electric dipole moment, Rabi spectrometers with electrostatic quadrupole deflection fields offer the possibility to detect rotationally inelastic collisions since the focusing and deflecting properties of the quadrupole field depend on the quantum state J, M) of a polar molecule. This technique is, however, restricted to molecules with a large electric dipole moment and to small values of the rotational quantum number J [1076]. 

A magnetic mass analyser is considerably more expensive and physically larger than its quadrupole counterpart. In normal operation the ion source operates at a high positive voltage, so that the monochromator interface region must be carefully designed to ensure that photoelectrons ejected from either the photodetector or any metal surfaces are not accelerated into the ion source to produce spurious ionization. For maximum ion transmission it is necessary to use an ion-optical lens, such as an electrostatic quadrupole, to focus the ions from a wide area into the narrow entrance slit of the mass spectrometer. The magnetic mass spectrometer, unlike a quadrupole... 

Through the use of sequential electric (electrostatic) and magnetic fields (sectors) and various correcting lenses, the ion beam leaving the ion source can be adjusted so that it arrives at the collector in focus and with a rectangular cross-section aligned with the collector slits. For the use of crossed electromagnetic fields. Chapter 25 ( Quadrupole Ion Optics ) should be consulted. 

Mass spectrometer configuration. Multianalyzer instruments should be named for the analyzers in the sequence in which they are traversed by the ion beam, where B is a magnetic analyzer, E is an electrostatic analyzer, Q is a quadrupole analyzer, TOP is a time-of-flight analyzer, and ICR is an ion cyclotron resonance analyzer. For example BE mass spectrometer (reversed-geometry double-focusing instrument), BQ mass spectrometer (hybrid sector and quadrupole instrument), EBQ (double-focusing instrument followed by a quadrupole). 

No one single mass analyzer is suitable for all applications and the choice of instrument is determined by the type of problem under investigation [68]. Double focusing magnetic/electrostatic sectorfield-, quadrupole-, quadrupole ion trap-, time-... 

The tandem MS includes a quadrupole mass filter, an octopole ion guide," a second quadrupole mass filter, and an ion detector. The ions from the flow tube are focused through electrostatic lenses into the first quadrupole, where a particular reactant ion is selected. These ions are then focused into the octopole, which passes through a cell that contains the collision gas. From the octopole, the dissociated and unreacted ions are focused into a second quadrupole for mass analysis. The detector is an electron multiplier operating in pulse-counting mode. 

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