Graphite electrothermal atomizers

Electrothermal Atomizers A significant improvement in sensitivity is achieved by using resistive heating in place of a flame. A typical electrothermal atomizer, also known as a graphite furnace, consists of a cylindrical graphite tube approximately... 

Gran plot a linearized form of a titration curve, (p. 293) graphite furnace an electrothermal atomizer that relies on resistive heating to atomize samples, (p. 414) gravimetry any method in which the signal is a mass or change in mass. (p. 233)... 

ELECTROTHERMAL ATOMIZATION IN GRAPHITE FURNACE A KINETIC MODEL WITH TWO INDEPENDENT SOURCES... 

After a brief period of use, the graphite tubes and rods that are commonly employed In electrothermal atomizers begin to deteriorate, and their electrical characteristics become subject to drift (7,9,47). This is one of the most troublesome sources of analytical variability. Maessen et al (47) demonstrated that the properties of graphite (e.g. porosity ancl conductivity)... 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

Cimadevilla et al. [691] compared wall, platform, and graphite furnace probe atomisation techniques in electrothermal atomic absorption spectrometry for the determination of ig/l levels of silver, cadmium, and lead in seawater. 

Batley [28] examined the techniques available for the in situ electrodeposition of lead and cadmium in estuary water. These included anodic stripping voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen and in situ electrodeposition on mercury coated graphite tubes. Batley [28] found that in situ deposition of lead and cadmium on a mercury coated tube was the more versatile technique. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals were then determined by electrothermal atomic absorption spectrometry, Hasle and Abdullah [29] used differential pulse anodic stripping voltammetry in speciation studies on dissolved copper, lead, and cadmium in coastal sea water. 

Conventional flame techniques present problems when dealing with either small or solid samples and in order to overcome these problems the electrothermal atomization technique was developed. Electrothermal, or flameless, atomizers are electrically heated devices which produce an atomic vapour (Figure 2.36). One type of cuvette consists of a graphite tube which has a small injection port drilled in the top surface. The tube is held between electrodes, which supply the current for heating and are also water-cooled to return the tube rapidly to an ambient temperature after atomization. 

A comprehensive review of electrothermal atomization devices has been published (94). The review includes a discussion of commonly encountered problems such as atom loss through non-pyrolytic graphite, non-isothermal conditions, differences in peak height and peak area measurement, etc. 

Describe a typical electrothermal atomizer for atomic absorption spectrometry. Critically compare graphite furnaces, air-acetylene flames, and nitrous oxide flames as atom cells for atomic absorption spectrometry. 

GD, 112-113,113(f) dark space, 112 Grimm source, 112 sputtering, 112 Glow discharge. See GD Graphite furnace. See Electrothermal atomizers Gratings. 

Figure 21-10 Reduction of interference by using a matrix modifier, (a) Graphite furnace temperature profile for analysis of Mn in seawater, (b) Absorbance profile when 10 xL of 0.5 M reagent-grade NaCl is subjected to the temperature profile in panel a. Absorbance is monitored at the Mn wavelength of 279.5 nm with a bandwidth of 0.5 nm. (c) Reduced absorbance from 10 nl of 0.5 M NaCl plus 10 of 50 wt% NH4NO3 matrix modifier. [From M. N. Quigley and F. Vernon, "Matrix Modification Experiment lor Electrothermal Atomic Absorption Spectrophotometry." J. Chem. Ed. 1996, 73. 980.]...

U. Schaffer and V. Krivan, Analysis of High Purity Graphite and Silicon Carbide by Direct Solid Sampling Electrothermal Atomic Absorption Spectrometry, Fresenius J. Anal. Chem. 2001,371, 859 R. Nowka and... 

Conventional AA instruments (Figure 1) use a flame atomization system for liquid sample vaporization. An air-acetylene flame (2300°C) is used for most elements. A higher temperature nitrous oxide-acetylene flame (2900°C) is used for more refractory oxide forming elements. Electrothermal atomization techniques such as a graphite furnace can be used for the direct analysis of solid samples. 

Hinds et al. [116] investigated the application of slurry electrothermal atomic absorption spectrometry to the determination of lead in soils. Hinds and Jackson [117] also investigated the application of vortex mixing slurry graphite furnace atomic absorption spectrometry to the determination of lead in soils. 

AMS = accelerated mass spectroscopy EDTA = ethylene diamine tetra acetic acid GFAAS = graphite furnace atomic absorption spectrometry ICP-AES = inductively coupled plasma - atomic emission spectroscopy NAA = neutron activation analysis ETAAS = electrothermal atomic absorption spectrometry SEC/ICP-MS = size-exclusion chromatography/ICP-AES/mass spectrometry HLPC/ICP-AES = high-performance liquid chromatography/ICP-AES LAMMA = laser ablation microprobe mass analysis NA = not applicable ppq = parts per quadrillion... 

Notes HG-AAS, Aydride generation atomic absorption spectrometry HG-AFS, /tydride generation atomic fluorescence spectrometry FI-CV-AAS, flow-injection cold-vapor atomic absorption spectrometry FAAS,flame atomic absorption spectrometry GF-AAS, graphite furnace atomic absorption spectrometry and ET-AAS, electrothermal atomic absorption spectrometry. 

Batley, G.E. and J.P Matousek. 1980. Determination of chromium speciation in natural waters by electrodeposition on graphite tubes for electrothermal atomization. Anal. Chem. 52 1570-1574. 

P. Bermejo Barrera, T. Pardinas Alvite, M. C. Barciela Alonso, A. Bermejo Barrera, J. A. Cocho de Juan, J. M. Fraga Bermudez, Vanadium determination in milk by atomic absorption spectrometry with electrothermal atomization using hot injection and preconcentration on the graphite tube, J. Anal. Atom. Spectrom., 15 (2000), 435-439. 

A. A. Almeida, M. I. Cardoso, L. F. C. Lima, Improved determination of aluminium in Port wine by electrothermal atomic absorption spectrometry using potassium dichromate chemical modification and end-capped graphite tubes, J. Anal. Atom. Spectrom., 12 (1997), 837-840. 

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