Reduction of spectral interferences in flame emission spectrometry by selective spectral-line modulation

Spectral interferences in flame emission spectrometry can be significantly reduced through the use of selective spectral-line modulation (s.l.m.). In this method, a mirrored, rotating chopper is used to direct the emission from a sample flame alternately through and around a second (modulating) flame; selective modulation is achieved when the modulating flame contains absorbing atoms identical to emitting analyte atoms in the sample flame. The effects of optical configuration and modulating conditions on working curve slope, linearity, and signal-to-noise ratio are examined. Also, the ability of s.l.m. to minimize broad-band and narrow-line spectral interferences is demonstrated. In particular, it has been shown that the interference of the 554-nm CaOH band on barium determinations can be largely overcome. Also, interference of several palladium lines on nickel in the 350-nm region can be reduced. Finally, it is shown how the interference of flame background itself can be restricted in s.l.m. procedures.