14.11 : Atomic Emission Spectroscopy: Interference

In atomic emission spectroscopy (AES), high-temperature atomizers excite a broad range of elements and molecules that generate complex emissions from sources such as oxides, hydroxides, and flame combustion products in the flame or plasma. Several strategies can be employed to minimize spectral interferences caused by overlapping emission lines or bands. These include increasing instrument resolution, choosing alternative emission lines, optimally placing the detector in low-background regions, or applying background correction techniques.

Chemical interferences occur when the analyte and other species in the flame react, forming stable compounds that do not dissociate, altering the analyte signals. These chemical interferences can often be eliminated or moderated using higher temperatures or releasing agents that selectively react with the interferent to release the analyte. Plasma sources contain abundant electrons, which help to offset ionization interference. Introducing easily ionizable elements into samples and standards also counteracts chemical interferences and improves sensitivity.

Organic solvents enhance the spectral line intensities due to higher flame temperature, faster feed rate, and smaller droplets in the aerosol. However, salts, acids, and other dissolved species may depress emission intensity, necessitating careful sample/standard matching. Fewer species remain stable in plasma, reducing interference from inorganic anions, organic solvents, and other dissolved species.

Further, the ground state analyte atoms in the outer flame regions may absorb the radiation emitted by the excited atoms in the flame center, decreasing emission intensity. However, this is less likely in plasma because of the shorter path length and more uniform temperature.