QUANTITATIVE INSITU SPECTROSCOPIC MEASUREMENTS AND THERMODYNAMIC EQUILIBRIA MODELING OF CN AND C2 IN A GRAPHITE-FURNACE

The principal objectives were to measure the in situ absolute steady-state levels of C2 and CN in a graphite furnace under varying working conditions (temperatures, gas compositions, samples), and to describe the experimental data with a thermodynamic equilibrium model. In an empty atomiser at 3000 K, the partial pressure of C2 was found to be at heterogeneous equilibrium. For CN, the partial pressure increased with temperature from 5 to 25% of the model value at 2300 and 2600 K, respectively. The CN level was shown, experimentally and by modelling, to be sensitive to the presence of oxygen. The partial pressure of CN exhibited a gradient between the tube wall and the centre of the tube. It is shown that the CN level inside the graphite tube can be used as an indicator for air ingress. The side-heated atomiser was compared in this respect to a Massmann-type furnace. The matrix modifiers Mg (NO3)2 and (NH4)2 HPO4 are shown to reduce the partial pressure of CN under the atomisation step, which may be of importance for atomisation efficiencies of analytes susceptible to cyanide formation.