The Second Skimmer

Fig. 15.12. Ion extraction interface for ICP-MS. Ions arrive from the ri t, a small portion is transmitted through the water-cooled sampling cone into the first pumping stage (rotary pump), the center of the free-jet expansion is then transmitted through the second skimmer cone, behind which it is guided by electric potentials through the second pumping stage into the mass analyzer. Reprinted with permission from Ref. [3]. John Wiley Sons Ltd., 1997.

SP Packs may be effectively multistaged, as shown in Figure 3.31. As shown in Figure 3.32, a two-stage system may consist of an SP Pack, a skim vessel, a second SP Pack, and a second identical skim vessel. One SP Pack and skimmer combination constitutes one stage of coalescence and separation. The second SP Pack coalesces the small oil droplets in the first skimmer s outlet then the second skimmer may remove the larger oil droplets. 

The addition of the SP Pack greatly improves the oil removal in the second skimmer because of coalescence. If the second SP Pack were not in the system, all the large oil droplets would be removed in the first skimmer and the second skimmer would remove little oil. Any number of stages in series may be used in the system. 

The beam from the first skimmer is directed toward a second one (Figure 12.1), again across an evacuated region where almost all of the residual solvent and helium are pumped away to leave a... 

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. 

Figure 5. Front end of triple a quadrupole mass spectrometer with an ion source and reaction chamber (see Figure 4) mounted in front of an evacuated space containing skimmer cone CB, AC only quadrupole lens Qo, and first quadrupole Qi. The second and third quadrupoles, Q2 and Q3, are not shown. CR denotes cryopumping surfaces. IQ is an interquad lens.

The molecular beam is formed by supersonic expansion from a heated oven source (i), shown in Fig. 3. The expansion is then collimated by a skimmer to form the molecular beam solid Une) as it passes from the source chamber (2) into the source differential region (J). From there the molecular beam passes through a second skimmer into the main chamber 4). The laser light travels in a direction perpendicular to the plane of the drawing in Fig. 3 and crosses the molecular beam at (5). This point is also on the axis of the detector, which is denoted by the dashed line. The oven source and separately pumped source and source-differential chambers are rotatable as a unit about the axis down which the laser beam travels. Ths rotation allows the molecular beam to detector angle 0 to be varied. 

The molecular beam extracted by a skimmer is interrogated in two different ways. First, an Nd YAG laser is used to ionize the species of interest. Second, in order to carry out photodepletion experiments, the second-harmonic output of the same Nd YAG laser is split into two beams, one of which is doubled to give... 

In ICP-MS. the ions formed in the ICP are extracted with the aid of a sampler into the first vacuum stage, where a pressure of the order of 100 Pa is maintained. Here, a supersonic beam is formed and a number of collision processes take place as well as an adiabatic expansion. These processes, together with their influence on the ion trajectories in the interface and behind the second aperture (skimmer), are very important for the transmission of ions and for related matrix interference [300]. Today s commercially available instrumentation falls into two groups quadrupole and high-resolution instruments. 

Durkee, J. (2008). The Second Cleaning Process The Oil Skimmer—Part II. Metal Finishing, 106(7-8), 69-71. 

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