Mechanism of spike formation in the process of reduction of oxides by carbon in graphite furnace atomic absorption spectrometry

Abstract

It is shown that the reduction of manganese and aluminium oxides by carbon, which manifests itself as spikes on the absorption signals of these elements, causes a delay in the vaporisation of gold and palladium injected separately into the same furnace. This effect is attributed to the formation of a carbon film on the metal particles of gold and palladium owing to the decomposition of the excess of manganese and aluminium gaseous carbides formed at the moment of the appearance of the spikes. In addition to this effect, under identical experimental conditions, reverse spikes of gold and palladium absorption signals coincident in time and shape with the manganese and aluminium spikes are observed. They appear to be associated with the formation of gaseous gold and palladium carbides. A general scheme of spike formation is outlined taking into account these results and data in the literature. It is determined by the autocatalytic development of the reduction process on the one hand and by the formation of a carbon film on the oxide particles on the other. The duration of oxidation of the carbon film on the oxide particles determines the intervals between the spikes. Some features of the phenomenon connected with the effect of the structure and distribution of the sample particles on the formation of the spikes are interpreted. Conditions for the vaporisation of the entire sample as a single spike have been found.