Introduction of sample stream air into an argon inductively coupled plasma permits continuous monitoring of hazardous air pollutant metals in combustion flue gases. Along with entrained particulates and metal vapors, various molecular components of the flue gas are introduced into the plasma. These species, and reaction products thereof, also undergo excitation resulting in complex emission spectra of appreciable intensity. Serious spectral interferences arise for several metal elements, from molecular emission bands associated with the stable CN radical and other polyatomic species. Failure to account for these interferences can significantly degrade accuracy particularly at low flue gas metal concentrations. Reported here is an effective method for measurement and correction of CN spectral interferences affecting the on-line detection of hazardous air pollutant metals that incorporates conventional polychromator hardware and existing instrument software capabilities. A demonstration of the ability of this method to achieve virtually complete correction of these interferences under both laboratory and field conditions is presented.

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