Influence on Dissociation Equilibria

The influence of other elements present in the flame or graphite furnace on the dissociation equilibria of the analyte can be a significant cause of chemical interference. As the absorption requires that the analyte prevails in the atomic state, dissociation of its compounds must occur, following for example the equations  

However, since the alkaline earth metal oxides in particular are comparatively stable, molecular bands, arising from metal oxides or hydroxides, are frequently observed in the spectra of these elements. In contrast to this, the oxides of alkali metals are less stable, resulting in strong atomic lines. 

A similar mechanism of interaction explains the increase in the response of vanadium in the presence of aluminum or titanium. This effect is observed more markedly in fuel rich flames and depends critically on the concentration of oxygen-containing species (Ox), such as O and OH, in the flame. In the flame, the dissociation equihbria of the three metals 

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In addition to spectral interferences, chemical interferences are also significant in AA spectrometry. Although in many instances, they can be reduced by judicious optimisation of the operating conditions. Chemical interferences are observed in atomic absorption spectrometry as a consequence of (a) formation of compounds of low volatility, (b) influence on dissociation equilibria, and (c) ionisation of the analytes. 

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