Interface skimmer cone

The coUision/reaction interface, which will be discussed later in this chapter, uses a slightly different principle to remove the interfering ions. It does not use a pressurized cell before the mass analyzer, but instead, injects a collision/reaction gas directly into the aperture of the interface skimmer cone. The injection of the collision/reaction into this region of the ion beam produces collisions between the argon gas and the injected gas molecules, and as a result, argon-based polyatomic interferences are destroyed or ranoved before they are extracted into the ion optics. 

The part that marries the plasma to the mass spectrometer in ICPMS is the interfacial region. This is where the 6000° C argon plasma couples to the mass spectrometer. The interface must transport ions from the atmospheric pressure of the plasma to the 10 bar pressures within the mass spectrometer. This is accomplished using an expansion chamber with an intermediate pressure. The expansion chamber consists of two cones, a sample cone upon which the plasma flame impinges and a skimmer cone. The region between these is continuously pumped. 

Figure 1. Nano-electrospray source assembly. The sample capillaries are disposable. The capillary tip is touched against the interface to initiate flow. Voltage is then applied and the capillary is positioned in front of the skimmer cone to obtain signal.

The plasma/mass spectrometer interface allows the import of a stream of ions from the plasma, at atmospheric pressure, into the mass spectrometer, which is under vacuum. The interface has a sample cone and a skimmer cone, usually of nickel and typically with 1.0 mm and 0.8 mm apertures, respectively. The turbomolecular pump is presently the most widely used type in the vacuum system. 

Figure 10.35 Close-up of the ICP-MS interface, showing the sampler and skimmer cones. [Courtesy of PerkinElmer Instruments, Shelton, CT (http //las.perkinelmer.com).]...

Diagram an ICP-MS interface. What is the purpose of the sampler and skimmer cones ... 

Figure 5.15 (a) Sketch of a gas curtain interface for API-MS coupling (Buckley 1974, 1974a French 1977). The ultra-dry gas (N2) curtain separates the ionization chamber (atmospheric pressure) from the orifice leading to the skimmer cone and thence to the mass spectrometer vacuum, (b) Sketch of an API-MS interface based on a heated glass capillary that connects the atmospheric pressure source to the low vacuum region preceding the sampling cone (Figure 5.17). In both cases an electric field E helps direct the ions into the sampling orifice. Reproduced from Bruins, Mass Spectrom. Revs. 10, 53 (1991), with permission of John Wiley Sons, Ltd.

So-called in-source CID occurs in the vicinity of the skimmer cone in API interfaces (e.g. Figure 6.40(b)) where the background pressure is comparable to that in a q collision cell (mtorr range). A potential is normally applied to the skimmer cone to permit gentle collisional activation that leads to stripping of clustered solvent molecules from the analyte ions (see Section 5.3.3a), but by increasing this potential (referred to as the cone potential or skimmer potential ) it is possible to increase the... 

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