Influence of Water on Spatial Excitation Behavior in the DCP

Spatially resolved excitation temperatures and electron densities in the direct-current plasma (DCP) have been measured as a function of the amount of water introduced to the plasma. Both the excitation temperature and the electron density increase with the quantity of water introduced. The increase in these parameters is large for very low water introduction rates, but slows as the amount of water introduced is increased. A plateau is reached where the amount of water introduced no longer affects the electron concentration or excitation temperature. This plateau is reached at a water introduction rate significantly less than that normally used for routine analytical work.