Tube electrothermal

Electrothermal atomisers fall into two classes, i.e. filaments and furnaces. The former category includes all devices in which an electrically heated filament, rod, strip or boat is used and where the atomic vapour passes into an unconfined volume above the viewing area on the other hand, furnaces usually consist of an electrically heated carbon tube into which the sample is injected. The optical axis of the hollow-cathode lamp light beam passes through the centre of this tube. Electrothermal atomisers are connected to a programmable power supply such that the sample can be dried, ashed and atomised at preset temperatures and times. 

Needleman, H.L, Tuncay, O.C. and Shapiro. I.M. (1972). Lead level in deciduous teeth of urban and suburban American children. Nature 235,111-112 Nordahl, K., Radziuk, B.. Thomassen, Y. and Weberg, R. (1990). Determination of aluminium in human biopsy and necropsy specimens by direct solid sampling cup in tube electrothermal atomic absorption spectrometry, Fres. Z. Anal. Chem. 337, 310-312 Nurnberg, H.W. (1981). in Faccheti, S. (ed.). Analytical techniques for heavy metals in biological fluids, lectures of a course held at the Joint Research Centre, Ispra, Italy, 22-26 June, Elsevier, Amesterdam... 

Kirkbright. G.F.. Chuan. S.H. and Snook. R.D. (1980) An evaluation of some matrix modification procedures for the use in determination of mercury and selenium by atomic absorption spectroscopy with a graphite tube electrothermal atomizer. Atom. Spec-trosc.. 1. 85-89. 

The introduction of atomic absorption spectrometry in 1955 by Walsh has brought about a preferred analytical technique among clinical chemists in the field of element determinations. Flame atomic absorption atomization techniques with solution aspiration is not sufficiently sensitive (detection limits varies from 0,05-3 mg Se/L for most clinical applications where sub-mg/L concentrations are encountered. The sensivity can, however, be improved by generation of volatile selenium hydride and subsequent atomization in argon-hydrogen flames or electrically heated quartz tubes. Electrothermal atomization of solutions in graphite tubes has developed rapidly since the analytical use was first proposed and studied by L vov (1961). For most clinical chemists this technique may be the most appropriate technique to analyze samples for low concentrations of selenium. 

The typical change in the total number of analyte atoms, N t), in the tube electrothermal atomizer obtained by convolution [1] of the supply function... 

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.

Goltz, D. M., Chakrabarti, C. L., Gregoire, D. C., and Byrne, J. P. (1995). Vaporization and atomization of uranium in a graphite tube electrothermal vaporizer A mechanistic study using electrothermal vaporization inductively coupled plasma mass spectrom-... 

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... 

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. 

Reactor 1 [R 1] Electrothermal Tubing-based Micro Reactor... 

Reactor type Electrothermal tubing-based micro reactor Tubing length 1.5 m... 

Figure 4.1 Flow scheme of a plant comprising an electrothermal tubing-based micro reactor configured for ethylene polymerization [1],...

The volume of the injection loops amounted to 20 pi the catalyst stream was set to 50 pi min In an electrothermal pre-heat zone the ethylene/comonomer mixture in toluene was brought close to reaction temperature before adding catalyst. The reaction was carried out at 175 °C and a pressure of 2.8 MPa. In several subsequent zones each of 16 cm length (volume 200 pi) along the reactor tubing, temperature was monitored by voltage pads. 

Aguilera de Benzo Z, Fraile R, Carrion N, et al. 1989. Determination of lead in whole blood by electrothermal atomization atomic absorption spectrometry using tube and platform atomizers and dilution with Triton X-100. Journal of Analytical and Atmospheric Spectrometry 4 397-400. 

Batley and Matousek [390,778] examined the electrodeposition of the irreversibly reduced metals cobalt, nickel, and chromium on graphite tubes for measurement by electrothermal atomisation. This method offered considerable potential for contamination-free preconcentration of heavy metals from seawater. Although only labile metal species will electrodeposit, it is likely that this fraction of the total metal could yet prove to be the most biologically important at the natural pH [779]. 

Batley [780] 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 AAS. 

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. 

Nebulization is inefficient and therefore not appropriate for very small liquid samples. Introducing samples into the plasma in liquid form reduces the potential sensitivity because the analyte flux is limited by the amount of solvent that the plasma will tolerate. To circumvent these problems a variety of thermal and electrothermal vaporization devices have been investigated. Two basic approaches are in use. The first involves indirect vaporization of the sample in an electrothermal vaporizer, e.g. a carbon rod or tube furnace or heated metal filament as commonly used in atomic absorption spectrometry [7-9], The second involves inserting the sample into the base of the... 

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. 

To optimize the applicability of the electrothermal vaporization technique, the most critical requirement is the design of the sample transport mechanism. The sample must be fully vaporized without any decomposition, after desolvation and matrix degradation, and transferred into the plasma. Condensation on the vessel walls or tubing must be avoided and the flow must be slow enough for elements to be atomized efficiently in the plasma itself. A commercial electrothermal vaporizer should provide flexibility and allow the necessary sample pretreatment to introduce a clean sample into the plasma. Several commercial systems are now available, primarily for the newer technique of inductively coupled plasma mass spectroscopy. These are often extremely expensive, so home built or cheaper systems may initially seem attractive. However, the cost of any software and hardware interfacing to couple to the existing instrument should not be underestimated. 

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