MONTE-CARLO STUDY OF ANALYTE DESORPTION, ADSORPTION AND SPATIAL-DISTRIBUTION IN ELECTROTHERMAL ATOMIZERS - INVITED LECTURE

Monte Carlo simulations of electrothermal atomization are used to study the effects of surface re-adsorption and non-uniform spatial distribution as well as the interpretation of the activation energy of atomization and peak shapes. The work is based on an atomization model for Cu. The kinetic parameters are altered to follow their effect upon the measured activation energy of atomization and the spatial distribution inside the atomizer. For elements with similar desorption kinetics, re-adsorption shifts the peak to higher temperatures (later times). The width of the peak increases with an accompanying decrease in peak height. Similar activation energies for atomization can be obtained from the linear region at the beginning (i.e., early in time) of Smets and Arrhenius plots. These plots are methods that deal with the initial rates and neither linearity nor accuracy should necessarily be expected after the initial portion of the graphs. The activation energy for atomization gives an estimation of the energy barrier for desorption but the adsorption barrier is not available from these plots. Spatially resolved atomization profiles show defined trends during the rising portion as well as at the peak. Stronger interactions with the graphite surface produce a steeper gradient in the gas phase at the beginning of the atomization. The accuracy of the estimation of this energy barrier can be significantly affected by the viewing position of the spectrometer system.