What is the Inductively Coupled Plasma?

The inductively coupled plasma is an argon plasma maintained by the interaction of an RF field and ionized argon gas. The ICP is reported to reach temperatures as high as 10,000K with the sample experiencing useful temperatures between 5,500K and 8,000K. These temperatures allow complete atomization of elements, minimizing chemical interference effects.

The plasma is formed by a tangential steam of argon gas flowing between quartz tubes, as show in Figure 1. Radio frequency (RF) power is applied though the coil, and an oscillating magnetic field is formed. The plasma is created when the argon is made conductive by exposing it to an electrical discharge which creates seed electrons and ions. Inside the induced magnetic field, the charge particles (electrons and ions) are forced to flow in a closed annular path. As they meet resistance to their flow, heating takes place and additional ionization occurs. The process occurs almost instantaneously, and the plasma expands to its full dimensions.

As viewed from the top, the plasma has a circular "doughnut" shape. THe sample is injected as an aerosol though the centre of the doughnut. This characteristic of the ICP confines the sample to a narrow region and provides an optically thin emission source and a chemically inert atmosphere. This results in wide dynamic range and minimal chemical interactions in an analysis. Argon is also used as a carrier gas for the sample. Fig2 is a magnificent picture of an actual plasma.


Figure 2
Figure 1 -  ICP torch assembly