| Abstract | The distributions of atomic and molecular species of boron inside a graphite furnace were investigated with a charge-coupled device (CCD) camera. Extensive spatial nonuniformity of the distributions at high temperatures was observed for both species. Digital imaging by the CCD camera showed that molecular boron species are preferentially formed at the top of the graphite tube at 1800-2000°C and their concentrations increase toward the center of the tube. The lowest concentrations of molecular boron species occur at the furnace walls and especially at the bottom of the graphite furnace. The highest concentrations of boron atoms occur along the graphite tube walls, at the bottom. The absence of significant concentrations of molecular species desorbing from the initial site of analyte deposition suggests that the analyte boron species, which do not absorb light at 254 nm, are vaporized. Since the highest concentrations of the molecular boron species were detected away from the graphite tube wall, desorption of molecular boron species is not likely. A gas-phase thermal dissociation of boron oxide species, resulting in the formation of BO (g), is suggested at temperatures below the atomization temperature. Pre-atomization loss of boron as molecular boron species is clearly evident from the CCD images. The high appearance temperature (2300°C) and high concentrations of atomic boron at the graphite tube wall suggest that much of the atomic boron signal is probably the result of desorption of boron atoms from the decomposition of boron carbide (solid). |
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