Graphite furnace atomic adsorption

Larsen EH, Rasmussen L. 1991. Chromium, lead and cadmium in Danish milk products and cheese determined by Zeeman graphite furnace atomic adsorption spectrometry after direct injection or pressurized ahsing. ZLebensm Unters Forsch 192 136-141. 

Yamini, Y, Chaloosi, M. Ebrahimzadeh, H. (2002) Solid phase extraction and graphite furnace atomic adsorption spectrometric determination of ultra trace amount of bismuth in water samples. Talanta, 56,... 

Adsorptive cathodic stripping voltammetry has an advantage over graphite furnace atomic absorption spectrometry in that the metal preconcentration is performed in situ, hence reducing analysis time and risk of contamination. Additional advantages are low cost of instrumentation and maintenance, and the possibility to use adapted instrumentation for online and shipboard monitoring. 

ET-AAS with graphite furnace tubes constituted the analytical support for the speciation analysis of Al and the concomitant determination of Al (III) in tea infusions, as described by Alberti and coworkers [141], Lvov platforms incorporated into the graphite furnace atomizers enabled the authors to attain an LoD of 2 xg l-1 Al. The determination was not impaired by the relatively high solid contents. Adsorption of Al on ion Chelex-100 resin was employed to estimate the free metal content and the concentration and stability constants of complexed Al species. The metal is reported to be present in total concentrations from 0.09 to 0.26 mM, but mainly linked to strong complexes. Strong complexation is demonstrated by the inability of Chelex-100 to dissociate the complexes. These results are considered by the authors as an explanation of the low toxicity of the Al associated with tea infusions. The concentration of free Al was found to be very low (at the nM level). No structural or chemical information about the ligands was obtained from the method. 

Methods for quantitative analysis of Co indude flame and graphite-furnace atomic absorption spectrometry (AAS e.g., Welz and Sperling 1999), inductively coupled plasma emission spectrometry (ICP-AES e.g., Schramel 1994), neutron activation analysis (NAA e.g., Versieck etal. 1978), ion chromatography (e.g., Haerdi 1989), and electrochemical methods such as adsorption differential pulse voltammetry (ADPV e.g., Ostapczuk etal. 1983, Wang 1994). Older photometric methods are described in the literature (e.g.. Burger 1973). For a comparative study of the most commonly employed methods in the analysis of biological materials, see Miller-Ihli and Wolf (1986) and Angerer and Schaller... 

Physical methods utilizing neutron activation, atomic emission spectrometry, graphite furnace atomic absorption spectrometry and adsorptive inverse voltammetry are presently used. Neutron activation determination seems to be the most reliable method for the analytical determination of vanadium in biological specimens taken from occupationally nonexposed and exposed people (Allen and Steinnes, 1978 Glyseth et al., 1979). In... 

At present, the most commonly used techniques for the determination of vanadium are graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma emission spectrometry (ICP-AES) and adsorptive inverse voltammetry (Fleischer et al., 1991). 

Much more sensitive and less time-consuming techniques such as mass spectrometry, atomic emission, and atomic absorption are needed for the analysis of pollutants. Detectors such as graphite furnace-atomic absorption spectrometer (GF-AAS), inductively coupled plasma-mass spectrometer (ICP-MS), or inductively coupled plasma-atomic emission spectrometer (ICP-AES) seem to be ideal candidates for the analysis of trace metals because of their very low detection hmits. The high temperatures used avoid the need for tedious digestions in many samples. FFF-gas chromatography-mass spectrometry could perhaps be used in the analysis of particular organic molecules. Another extremely sensitive technique applied in the study of adsorption behavior of pollutants is to add radiolabeled adsorbates (such as P04, " C-atrazine, and ""C-glyphosate ) to study the distribution of the pollutant as a function of size. 

The chemical speciation of copper in river water and model solutions was investigated by a titration technique in which cupric ion activities were measured at constant pH as the total copper concentration ([Cujoj]) was varied by incremental additions of CUSO4. pCu(-log cupric ion activity) was measured with a cupric ion-selective electrode (Orion 94-29) and pH with a glass electrode (Beckman 39301) both coupled to a single junction Ag/AgCl reference electrode (Orion 90-01) in a temperature controlled (25 + 0.5°C) water bath. Total copper concentrations in the titrated solutions were determined directly by atomic absorption spectrophotometry (Perkin Elmer 603) using a graphite furnace (Perkin Elmer 2200). Measurement of total copper concentrations is necessary because of adsorptive loss of copper from solution onto container and/or electrode surfaces. 

A method has been developed for differentiating hexavalent from trivalent chromium [33]. The metal is electrodeposited with mercury on pyrolytic graphite-coated tubular furnaces in the temperature range 1000-3000 °C, using a flow-through assembly. Both the hexa- and trivalent forms are deposited as the metal at pH 4.7 and a potential at -1.8 V against the standard calomel electrode, while at pH 4.7, but at -0.3 V, the hexavalent form is selectively reduced to the trivalent form and accumulated by adsorption. This method was applied to the analysis of chromium species in samples of different salinity, in conjunction with atomic absorption spectrophotometry. The limit of detection was 0.05 xg/l chromium and relative standard deviation from replicate measurements of 0.4 xg chromium (VI) was 13%. Matrix interference was largely overcome in this procedure. 

Fig. 11 Surface fractal dimensions ds on atomic length scales of furnace blacks and graphitized blacks in dependence of specific surface. The data are obtained from nitrogen adsorption isotherms in the multilayer regime...

Figure 3 Schematic representation of the basic physical and chemical processes taking place in a tube electrothermal atomizer. Solid arrows denote pathways of free analyte atoms, dotted arrows show the pathways of the analytes that are bound into molecules. Primary generation of the analyte vapour from the site of sample deposition as an atomic (1) or a molecular (1 ) species. Irreversible loss of analyte from the furnace through its ends (2) and through the sample dosing hole (2 ) by diffusion and convection. Physical adsorption/desorptlon at the graphite surface (3). Gas phase condensation (4) at the cooler parts of the atomizer. Gas phase reactions (5) that bind free analyte atoms into stable molecules or those (S ) that increase the free atom density. Heterogeneous reactions of analyte vapour with the atomizer walls includes both production (6) and loss (6 ) of free atoms at the furnace wall.

Atomic absorption spectrometry furnace tubes are supplied with a hard pyrolytic graphite surface. This helps to reduce the porosity of the tube, which minimizes adsorption of hot metal vapors and slows down the rate of oxidation of the graphite and the accompanying mechanical degradation of the furnace tube. 

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