Vapor expulsion and loss from a graphite furnace atomizer

doi:10.1016/0584-8547(83)80035-4

Spectrochimica Acta Part B: Atomic Spectroscopy

Volume 38, Issue 4, 1983, Pages 609-615

https://doi.org/10.1016/0584-8547(83)80035-4 Get rights and content

Abstract

The independent effects of analyte loss by diffusion, thermal expansion, and expulsion caused by gas evolution from the matrix have been studied. Experimentally isolating these phenomena is nearly impossible and models have been used to ascertain the impact of these individual processes. Under most conditions thermal expansion of the gas within the furnace volume during ramp heating contributes significantly to analyte ejection. The thermal expansion loss becomes increasingly important for volatile metals and high heating rates. Diffusion dominates for lower heating rates and elevated temperatures. Gas evolution by the matrix is significant in expelling the analyte from the furnace only when a near-coincidence in appearance times of analyte and matrix exist. Strong dependencies also are exhibited by the appearance temperature of the matrix gas and the evolution rate of the gas from the surface. Velocity profiles of gas within the furnace as well as the dependencies of these loss mechanisms on furnace geometries also are presented.

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Cited by (51)

Model calculation of the characteristic mass for convective and diffusive vapor transport in graphite furnace atomic absorption spectrometry
2015, Spectrochimica Acta - Part B Atomic Spectroscopy
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In the current study, the vaporization of the sample is considered as what occurs from either a non-point source (integrated graphite platform) or a point source, i.e., sample is place at the center of the graphite tube. Gilmutdinov et al. [32] have developed a model for the calculation of the three-dimensional distribution of free atoms and condensed particles in tube-type atomizers. The image representation of the calculated three-dimensional distribution of free silver atoms showed that during atomization the sample expands and fill in the whole volume of the graphite furnace.
A combination of former convective–diffusive vapor-transport models is described to extend the calculation scheme for sensitivity (characteristic mass — m₀) in graphite furnace atomic absorption spectrometry (GFAAS). This approach encompasses the influence of forced convection of the internal furnace gas (mini-flow) combined with concentration diffusion of the analyte atoms on the residence time in a spatially isothermal furnace, i.e., the standard design of the transversely heated graphite atomizer (THGA). A couple of relationships for the diffusional and convectional residence times were studied and compared, including in factors accounting for the effects of the sample/platform dimension and the dosing hole. These model approaches were subsequently applied for the particular cases of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn analytes. For the verification of the accuracy of the calculations, the experimental m₀ values were determined with the application of a standard THGA furnace, operating either under stopped, or mini-flow (50 cm³ min^− 1) of the internal sheath gas during atomization. The theoretical and experimental ratios of m₀(mini-flow)-to-m₀(stop-flow) were closely similar for each study analyte. Likewise, the calculated m₀ data gave a fairly good agreement with the corresponding experimental m₀ values for stopped and mini-flow conditions, i.e., it ranged between 0.62 and 1.8 with an average of 1.05 ± 0.27. This indicates the usability of the current model calculations for checking the operation of a given GFAAS instrument and the applied methodology.
Fast heating induced impulse halogenation of refractory sample components in electrothermal atomic absorption spectrometry by direct injection of a liquid halogenating agent
2011, Talanta
Citation Excerpt :
Then the next step would be the halogenation, which requires the fast heating of the graphite furnace to attain expansion of the halocarbon vapor. Holcombe [24] studied the expulsion of matrix vapors in an end-heated graphite tube atomizer under fast heating and observed analyte/matrix losses at the tube ends, due to vapor expansion. On the base of his study, it is expected that the residue of the chlorinating agent expands and fills in the whole volume of the graphite tube, when using fast heating and interrupted flow of the IFG, which exhibits the possibility of an efficient removal of the refractory sample components.
A novel electrothermal atomic absorption spectrometry (ETAAS) method was developed for the halogenation of refractory sample components (Er, Nd and Nb) of lithium niobate (LiNbO₃) and bismuth tellurite (Bi₂TeO₅) optical single crystals to overcome memory effects and carry-over. For this purpose, the cleaning step of a regular graphite furnace heating program was replaced with a halogenation cycle. In this cycle, after the graphite tube cooled to room temperature, a 20 μL aliquot of liquid carbon tetrachloride (CCl₄) was dispensed with a conventional autosampler into the graphite tube. The CCl₄ was partially dried at 80 °C under the mini-flow (40 cm³ min⁻¹) condition of the Ar internal furnace gas (IFG), then the residue was decomposed (pyrolyzed) by fast furnace heating at 1900–2100 °C under interrupted flow of the IFG. This step was followed by a clean-out stage at 2100 °C under the maximum flow of the IFG. The advantage of the present method is that it does not require any alteration to the graphite furnace gas supply system in contrast to most of the formerly introduced halogenation techniques.
The effectiveness of the halogenation method was verified with the determination of Er and Nd dopants in the optical crystals. In these analyses, a sensitivity decrease was observed, which was likely due to the enhanced deterioration of the graphite tube surface. Therefore, the application of mathematical correction (resloping) of the calibration was also required. The calibration curves were linear up to 1.5 and 10 μmol L⁻¹ for Er and Nd, respectively. Characteristic masses of 18 and 241 pg and the limit of detection (LOD) values of 0.017 and 0.27 μmol L⁻¹ were found for Er and Nd, respectively. These LOD data correspond to 0.68 μmol mol⁻¹ Er and 11 μmol mol⁻¹ Nd in solid bismuth tellurite samples. The analytical results were compared with those obtained by a conventional ETAAS method and validated with X-ray fluorescence spectrometry analysis.
Atomic Absorption Spectroscopy
2007, Food Toxicants Analysis: Techniques, Strategies and Developments
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Investigation of interference mechanisms of nickel chloride on copper determination and of colloidal palladium as modifier in electrothermal atomic absorption spectrometry using a dual cavity platform
2005, Spectrochimica Acta - Part B Atomic Spectroscopy
The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atomization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interferent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40–50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes.
Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry
2005, Spectrochimica Acta - Part B Atomic Spectroscopy
The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.

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Vapor expulsion and loss from a graphite furnace atomizer

Abstract

Anal. Chim. Acta

Vacuum

Spectrochim. Acta

Spectrochim. Acta