Application of Langmuir theory of evaporation to the simulation of sample vapor composition and release rate in graphite tube atomizers. Part 2. Verification of the methodology and investigation of atomization of Ag and Cu

Abstract

The Langmuir theory of metal evaporation in a foreign gas at atmospheric pressure was applied to the simulation of atomic absorption signals of Ag and Cu in the electrothermal atomizers for atomic absorption spectrometry. The selection of elements permitted simplification of the approach on account of a priori low contribution of oxygen and oxide molecules in the condensed and gas phases in the simulated processes. The model includes vaporization of both atoms and dimers and vapor transport complicated by interaction with graphite on the tube wall. The calculation program consists of a system of first order differential equations describing vaporization and vapor transport; it was solved numerically using MATLAB software on a desktop PC. The results were verified by comparison of the simulated absorption signals vs. time and vapor release rates vs. temperature with those obtained in the experiments with graphite or Ta-lined tubes. The simulation and experiments reveals the possibility for instant correction of the measured absorbance by vapor transportation velocity that makes peak area independent of the kinetics of atomic vapor release. The simulations and experimental data indicate the contribution of the molecular fraction in the vapor and chemical interaction of Cu and Ag vapor with graphite above 1400 K.