Interface region cones

Once the ions are produced in the plasma, they are directed into the mass spectrometer via the interface region, which is maintained at a vacuum of 1-2 torr with a mechanical roughing pump. This interface region consists of two metallic cones (usually nickel), called the sampler and a skimmer cone, each with a small orifice (0.6-1.2 mm) to allow the ions to pass through to the ion optics, where they are guided into the mass separation device. 

ICP-MS Besides the plasma torch and sample introduction supplies, ICP-MS requires consumables that are situated inside the mass spectrometer. The first area is the interface region between the plasma and the mass spectrometer, which contains the sampler and skimmer cones. These are traditionally made of nickel, which is recommended for most matrices, or platinum for highly corrosive samples and organic matrices. A set of nickel cones costs 700-1000, whereas a set of platinum cones costs about 3000-4000. Two sets of nickel cones and perhaps one set of platinum cones would be required per year. The other major consumable in ICP-MS is the detector, which has a lifetime of approximately 1 year, and costs about 1200-1800. Some systems also have a replaceable ion lens. It is suggested that five of these at 100 each are required for a routine laboratory. When all these are added together with the torch, the sample introduction components, and the vacuum pump consumables, investing in ICP-MS supplies represents an annual cost of 9,000-11,000. 

Debye length The distance over which ions exert an electrostatic influence over one another as they move from the interface region into the ion optics. In the ionsampling process, this distance is small compared to the orifice diameter of the sampler or skimmer cone. As a result, there is little electrical interaction between the ion beam and the cones, and relatively little interaction between the individual ions within the ion beam. In this way, the compositional integrity of the ion beam is maintained throughout the interface region. 

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. 

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