INVESTIGATION OF VAPOR CONDENSATION IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY BY THE SHADOW SPECTRAL DIGITAL IMAGING TECHNIQUE

Condensation of vapors of gold (analyte) and matrices of various chemi cal modifiers and compounds in graphite furnace atomic absorption spec trometry was investigated by using the shadow spectral digital imaging technique with a charge-coupled device camera. Spatial and temporal n onuniformity in the light scattering was observed, and these effects w ere attributed to the formation of condensed-phase particles during th e processes of high-temperature vaporization and atomization, The mate rials investigated were Au, MgCl2, NaCl, (NH4)(2)HPO4, La(NO3)(3), and a mixture Pd and Mg(NO3)(2). The nonuniform distributions of the cond ensed-phase particle clouds were attributed to the gas-flow patterns t hat 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 fur nace, Differences observed with fast and slow rates of heating were re lated to thermal expansion of gas and diffusion effects, Use of either a graphite platform or a low argon purge gas flow during the high-tem perature heating of the graphite furnace was found to reduce condensat ion of matrix vapor and to improve accuracy of continuum source backgr ound correction.