APPLICABILITY OF MICROWAVE-INDUCED PLASMA OPTICAL-EMISSION SPECTROMETRY (MIP-OES) FOR CONTINUOUS MONITORING OF MERCURY IN FLUE-GASES

The applicability of microwave-induced plasma optical emission spectro metry (MIP-OES) for continuous monitoring of the environmentally hazar dous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM(010) cavity (Beenakker re sonator) and a so-called Surfatron. The analytical figures of merit fo r mercury in argon and helium discharges with both types of low-power microwave discharges have been examined. To determine mercury in artif icial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a meta l-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concent ration < 6 g/m(3)), oxygen (< 4% v/v) and carbon dioxide (< 15% v/v) d ecrease the mercury line intensities to a considerable extent. Trace g ases (GO, HCl, SO2, NO) in concentrations typical to waste incineratio n processes have been found to have no effect on the mercury and the a rgon line intensities. The detection limit of mercury in nitrogen is 8 mu g/m(3) using the TM(010) MIP and 10 mu g/m(3) using the Surfatron. As such low detection limits are below the emission limit values of p resent-day environmental legislation MIP-OES is useful for on-line mon itoring of mercury.