In the past few years, on-line monitoring of the elemental pollutants in the flue gas of industrial plants has been developed. Several field tests have been carried out on
incineration plants or on various thermal processes. Such techniques are generally based on the injection of the gas to be analysed into an analytical lCP. The limits of detection observed are generally very low, similar to those obtained with classical argon ICP. However, when molecular species induce spectral interference with analytical lines, the detection limit fur the concerned element is strongly degraded. These molecular interferences depend on the nature of the gaseous matrix (the gas to be analysed), and on the operating conditions. Therefore the stability of the molecular species is linked to the plasma temperature in the analytical zone. It is such possible to reduce the interference varying generator power and flow rates. In the case of processes using only air, the main interferences are due to NO and N2+ bands. The elements the most affected are As and Pb. In the case of combustion gases, CN, CO and C2 are the most
disturbing molecules, and affect the analysis of elements like As, Sb, Ph, Hg, and Zn.