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induction. The inductively coupled and the microwave-induced plasma instruments are by far the most
common, and both instruments will be described.
The Microwave-induced Plasma (MIP) Atomic Emission Spectrometer in GC/ES Systems
The microwave-induced atomic emission spectrometer has been briefly described in Chapter 2, but the
actual interface, and the resonance cavity of the spectrometer, will be discussed further, in order to fully
understand its operating characteristics. The design chosen will be that developed relatively recently by
Quimby and Sullivan [1], which is similar to the system originally described by Beenakker [2,3]. A
diagram of the reentrant cavity of their emission spectrometer is shown in Figure 6.1 and, as its
construction is fairly critical, it will be described in some detail.
The cavity differs slightly from that of Beenakker, in that the pedestal is situated in the center of the
cavity, which is much smaller, and the coupling loop is much thicker. In addition, a quartz cooling
jacket is placed in the center of the cavity surrounding the discharge tube. The main body of the cavity
consists of a stainless steel block, with the cylindrical section and pedestal machined out of it, and a
cover plate. The two main cavity plates are fitted together with a silver-filled silicone rubber gasket to
ensure a good seal. The quartz water jacket (carrying water at 60°C) is situated between the two halves
of the cavity, and held in place by O-rings. The inlet and outlet water connections are radially drilled
through the stainless steel. Stainless steel plates are attached to the outside of both halves of the main
cavity, and sealed with two more O-rings. As a consequence, the water passes through an annular space
between the discharge tube and the water jacket and, in addition, the discharge tube is held
concentrically inside the water jacket.
The discharge tube is 4.2 cm long, 1.25 mm O.D., and 1.0 mm I.D., made of fused quartz coated with
polyimide. However, the polymer coating does not extend over that portion of the tube in which the
discharge is taking place. It is secured by a polyimide ferrule on the GC side of the tube and by a Viton
O-ring on the optical side of the tube, which is compressed by