Spectral Interferences:

These refer to the presence of other atomic absorption line or a molecular absorption band close to the spectral line of the analyte element being monitored. That qualifies to be interference if it is not resolved through the monochromator.  Most possible spectral interferences are the ones of the molecular emissions from oxides of other elements within the sample. In that case of AAS, such interferences occur if a dc instrument is used and could be eliminated through employing an ac instrument. Same a positive interference might occur if an element or molecule is capable of absorbing radiation from a continuous source. This might be minimised but not eliminated altogether through using a line source.

The other source of spectral interference is the light scattering or absorption by solid particles, unvaporised solvent droplets or molecular species in the flame. This problem is important at wavelengths less than 300 nm while solutions of high salt content are aspirated. This arises since of incomplete desolvation and is known background absorption or blank. This could be corrected through measuring the absorbance of a line close to the absorption line of the analyte element but not absorbed through the element itself. The measurements should be made at two other lines from the hollow cathode lamp or a nearby line from a second hollow cathode lamp. Analyte test element should always be aspirated to check in which it does not absorb the background correction line. This method needs two separate measurements on the sample.

A yet another source of spectral interference is the background emission from the flame. This might be corrected through modulation of the output of the radiation source and the ac detection system. Various background correction schemes have been developed and incorporated within spectrophotometers such as the deuterium background correction, Zeeman correction system and the Smith-Hieftie system. These are not discussed here; you can acquire information about these from the reference texts listed at the end of the block.