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very stable discharge using argon and helium as plasma gases. Uchida et al. [12] utilized the capacity
coupled microwave plasma system to provide multi-element detection for a capillary gas
chromatograph. It was employed very successfully for monitoring the elution of different halogenated
aromatic compounds and the separation of a group of these is shown in Figure 6.12. By monitoring on
both the chlorine and bromine lines, the compounds containing exclusively bromine or chlorine can be
clearly discerned form those compounds that contain both halogens. More importantly, it is seen that
the plasma persisted in a stable form throughout, and after, the elution of the pentane solvent which was
present in the plasma at a very high concentration.

Inductively Coupled Plasma (ICP) GC/ES Systems

The basic difference between the ICP torch and the MIC torch is the method of energy transfer, the
physical arrangement of both torches being fundamentally similar. In addition, the ICP torch may not
provide good spectra for the common elements, but is very sensitive to elements of higher atomic
weight and in particular the metallic elements. A diagram of the ICP torch is shown in Figure 6.13.

The ICP torch is often employed with a capillary column system, but can also be used with packed
columns providing argon is used as the carrier gas. The torch is made of three concentric tubes of silica,
through the center of which passes the column flow. If a capillary column is used, a scavenger flow of
argon must also be mixed with the carrier gas, to ensure the sample bands are swept cleanly from the
system, and do not accumulate in the torch. The next outer tube also furnishes make-up argon to
provide sufficient for forming a plasma, and also helps cool the inlet tube. The outer tube carries a large
flow of argon or nitrogen that keeps the temperature of the front part of the torch from reaching the
melting point of silica.

The high-frequency transducer consists of a few turns of a water cooled coupling coil, the rf power
being supplied by an appropriate frequency generator and power amplifier. Although energy transfer
between the