Atomization Mechanisms of Gold from Thermally Decomposed and Crudely Roughened Pyrolytically Coated Graphite Furnaces Using Electrothermal Atomization

Abstract

Studies of atomization mechanism of gold and silver in electrothermal atomization seek a better understanding of the atomic vapor formation process and the type of interactions taking place between the analyte and the surface of the atomizer. This type of information can lead to logical approaches for improvement of the technique or the method of analysis. Arthur and Cho 1 reported the adsorption and desorption kinetics of gold on a single graphite crystal where adsorbed atoms (adatoms) can move on the single-crystal graphite and form droplets or caps. Scanning tunneling microscopy supported the existence of adatoms, microdroplets and two-dimensional islands on graphite for several atoms including gold.2 In an electrothermal graphite furnace atomic absorption spectrometry, it has been reported by using kinetic analysis that the desorption of gold occurs from microdroplets as a solution deposition is used. [3][4][5][6] Fonseca and co-workers 7 reported that vaporization of gold and silver appears to occur from varying sizes of microdroplets or from adatoms, depending on the analytical conditions, such as dry and thermal pretreatment conditions, chemisorbed oxygen on the graphite surface and mechanically created active sites on the graphite surface. In the case of silver, although a tendency of the activation energy (E a ) for atomization to increase as the concentration increases was observed with a fractional order desorption, a constant E a was observed below 0.06 ng of silver, which is in agreement with the morphology of dispersed atoms with a first order desorption. Unlike silver, gold did not approach a constant E a at low absorbances. They suggested that confirmation of a constant E a corresponding to the morphology of dispersed gold atoms would require a more sensitive technique or different atomizer design.The graphite surface consists of crystallites of graphite with carbons lying in a basal plane which is terminated by carbons in zigzag and armchair configurations. The edge and terminated carbons have unpaired s electrons which constitute active sites and exist at lattice defects and at boundaries of graphite crystallites. The active surface area of graphite normally accounts for only a few percent of total surface area, depending on the conditions of the surface. The number of active site is increased by thermal treatment and mechanically roughening of the graphite surface. On the graphite surface rich in the active sites, the easy formation of a highly dispersed state of gold (i.e. adatoms) can be expected. It was found that a constant E a was observed at low concentrations by using thermally decomposed and crudely roughened PG furnaces, corresponding to the morphology of highly dispersed atoms of gold (i.e. individual adatoms). ExperimentalA Hitachi Model Z-8000 flame and graphite furnace atomic absorption spectrometer equipped with a Zeeman effect background corrector, an optical temperature controller system (Hitachi Model 180-0341) and an automatic data processor were used. Twenty microliters of a...

Simulation of atomic absorption signals: A kinetic model with two independent sources

“…4B). The similar phenomenon is observed also for Au (see, e.g., [38]). At the same time, for Cu (Fig.…”

Controlling atomizer surfaces by varying ascorbic acid pyrolysis conditions to modify activation energies for gold desorption in electrothermal atomic absorption spectrometry

“…When gold atoms are releasd from microdroplets, a mass dependency of E a was reported, 2,4 while no dependency was observed for gold desorption from monolayers on the graphite surface. 3 The independence of E a from the injected mass of gold (Table 4) is supported by the desorption of gold from monolayers.…”

“…Although the E a did not reach a constant value for gold deposited on a thermally decomposed, pyrolytically coated graphite (PG) surface, the E a reached a constant value for gold deposited on a crudely roughened PG surface, corresponding to adatoms of gold at active sites. 3 At this time a lowertemperature shift of the atomic absorption signal of gold was observed.…”

Electrothermal Atomic Absorption Spectrometry and Related Techniques

“…Gaseous dissociation of SeO 2 (where analyte loss may occur) is followed by the first-order desorption of Se from carbon. Imai et al (91) used Raman spectrometry to study the effects of multiple firings and physical roughening on the inner wall of a Massmann-type furnace and investigated the atomization of Au. This was of interest, since previous studies on the atomization of Au have indicated desorption from microdroplets or from adatoms, depending on analytical conditions and, particularly, on the number of active sites on the graphite surface.…”