Condensation of matrix vapours in the gaseous phase in graphite furnace atomic absorption spectrometry

The appearance of non-specific absorbance signals when μg-masses of elements (Ag, Au, Cu, Mg, Mn and Pd) are vaporized in graphite furnaces has been studied. It was shown that this phenomenon is common for all types of electrothermal atomizers irrespective of their construction (side-heated or end-heated HGA-type), furnace material or mode of operation (platform or wall evaporation, gas-stop or mini-flow). The phenomenon was interpreted, contrary to the previous soot formation hypothesis (B.V. L'vov et al., Spectrochim. Acta 46B, 1001 (1991)), as a result of condensation of metal (or oxide) vapours in the cooler zones of the furnace with formation of a particle cloud. Due to temperature inhomogeneity over the cross-section near the injection hole in HGA-type furnaces, condensation occurs not only at the tube ends but also in the centre. The importance of this phenomenon in an interpretation of the origin of the matrix background absorption and the under- or overcorrection effects observed with two-source background correctors, as well as in explaining some types of matrix interferences, was noted.