DIGITAL IMAGING OF FORMATION AND DISSIPATION PROCESSES FOR ATOMS AND MOLECULES AND CONDENSED-PHASE SPECIES IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY - A REVIEW

This is a review of our recent work in the use of a CCD-based digital imaging system for the shadow spectral digital imaging (SSDI) of boron , aluminium (spike formation), and condensation of vapour of selected analytes, matrices, and chemical modifiers in graphite furnace atomic absorption spectrometry (GFAAS). The use of a charge-coupled device (C CD) camera has enabled a number of processes in the Massmann-type GFAA S to be more thoroughly investigated than has been previously possible . The SSDI technique has been used to obtain spatially and temporally resolved distributions of atoms, molecules and condensed-phase species generated in a graphite furnace as a result of processes such as vapo rization, atomization and condensation. The application of this techni que to the investigation of atomic and molecular species of boron has helped in elucidating the mechanism of vaporization and atomization of boron. Thermal dissociation of boron oxide species results in the for mation of BO(g) and its loss from a graphite furnace at temperatures b elow the atomization temperature of boron. The atomic boron signal is the result of desorption of boron atoms from the decomposition of cond ensed-phase boron carbide. Studies using the CCD imaging of atomic and molecular species of aluminium in a graphite furnace have resulted in a mechanism being proposed for aluminium atom spike formation and for dissipation of aluminium atoms in the graphite furnace, aluminium ato m spikes formed from gaseous Al2O precursors, this reaction being trig gered by the formation of a condensed-phase Al4C3 melt. Finally, the S SDI technique has been used to further our knowledge and understanding of light-scattering of microparticles produced by condensation of vap ours of selected analytes, matrices and chemical modifiers. The spatia l and temporal non-uniformity of condensed-phase particle clouds are a ttributed to thermal expansion of gas, gas flow patterns and temperatu re gradients in the vapour phase and in the heated graphite tube which develop in the Massmann-type graphite furnace.