Chamber, beam entering

The beam entering the ion chamber is suitable for both electron (El) and chemical (Cl) ionization, and either mode can be used (Figure 12.3). Mass analysis follows in the usual way, typically using quadruple or magnetic-sector instruments. 

The particle beam interface is an example of an HPLC/MS interface (see Fig. 16.14). In this interface, the mobile phase is vaporised in the form of a spray into a desolvation chamber before entering the area where the sample is concentrated by evaporation. Because solvent molecules are lighter, their angular dispersion is wider than that of the analyte, which can be transferred into the transfer capillary. This type of interface is slowly being abandoned in favour of others that have a greater sensitivity. 

Fig. 1.23. The electron diffraction apparatus developed by Parks and coworkers includes an rf-ion trap, Faraday cup, and microchaimel plate detector (MCP) and is structured to maintain a cylindrical symmetry around the electron beam axis [147]. The cluster aggregation source emits an ion beam that is injected into the trap through an aperture in the ring electrode. The electron beam passes through a trapped ion cloud producing diffracted electrons indicated by the dashed hues. The primary beam enters the Faraday cup and the diffracted electrons strike the MCP producing a ring pattern on the phosphor screen. This screen is imaged by a CCD camera mounted external to the UHV chamber. The distance from the trapped ion cloud to the MCP is approximately 10.5 cm in this experiment...

A first laser beam enters the collision chamber perpendicularly to the plane of collisions and excites Cs atoms from 6S1/2 to TP /2 ot 7 3/2 according to its wavelength 459.3 nm or = 455.5 nm respectively. It is delivered by a single mode C.W. jet stream dye laser whose frequency is locked to the desired transition through a servo-controlled system alimented by the fluorescence light emitted by Cs atoms excited at the collision volume. 

From the ionization chamber, the beam of ions passes through a short field-free region. From fhere, fhe beam enters the mass analyzer, where the ions are separated according to their mass-to-charge ratio. 

The particle beam — after linear passage from the evacuation chamber nozzle, through the first and second skimmers, and into the end of the ion source — finally passes through a heated grid immediately before ionization. The heated grid has the effect of breaking up most of the residual small clusters, so residual solvent evaporates and a beam of solute molecules enters the ionization chamber. 

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