Investigation of Vapor Condensation in Graphite Furnace Atomic Absorption Spectrometry by the Shadow Spectral Digital Imaging Technique

Abstract

Condensation of vapors of gold (analyte) and matrices of various chemical modifiers and compounds in graphite furnace atomic absorption spectrometry was investigated by using the shadow spectral digital imaging technique with a charge-coupled device camera. Spatial and temporal nonuniformity in the light scattering was observed, and these effects were attributed to the formation of condensed-phase particles during the processes of high-temperature vaporization and atomization. The materials investigated were Au, MgCl2, NaCl, (NH4)2HPO4, La(NO3)3, and a mixture Pd and Mg(NO3)2. The nonuniform distributions of the condensed-phase particle clouds were attributed to the gas-flow patterns that developed in the graphite tube furnace during heating, as well as the steep temperature gradients that developed along the longitudinal axis of the end-heated graphite tube of the Massmann-type graphite furnace. Differences observed with fast and slow rates of heating were related to thermal expansion of gas and diffusion effects. Use of either a graphite platform or a low argon purge gas flow during the high-temperature heating of the graphite furnace was found to reduce condensation of matrix vapor and to improve accuracy of continuum source background correction.