Diffusion of molecular vapors through heated graphite

Abstract

The reasons for the elimination of interferences in a filter furnace used as an atomizer in electrothermal atomic absorption spectroscopy (ETAAS), are examined theoretically and experimentally. The results of observations of stepped or multipeak background absorption signals for NaCl, NaI, KCl, KBr, KI, CaCl 2 and MgSO 4, which are characteristic for each matrix and different types of graphite used, leads to hypotheses about the formation of molecule-graphite intercalation composites. These are treated as stable compounds of different stoichiometry having substantial specific enthalpy of formation. The validity of the idea is confirmed with the measurements of the rate of NaCl vapor release through a graphite filter as a function of temperature, and comparison with the literature data for similar compounds of alkali metals. The effect of implantation of molecular particles into a crystalline lattice leads to reduction of their diffusion rate through graphite, which in turn provides time-resolved background and atomic absorption signals. Further investigations and development of the idea to understand the analytical effect are proposed.