Tubes graphitic

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... 

Impervious graphite heat-exchanger equipment is made in a variety of forms, including outside-packed-head shell-and-tube exchangers. They are fabricated with impervious graphite tubes and... 

To understand the causes of signal change and therefore to explain the influence of physico-chemical factors on its shape and magnitude, the mathematical models are employed. A multitude of different and often contradictory models were proposed to describe the atom formation in ET AAS, but they do not take into account a number of effects influencing appreciably the atomic absorption profile. The surface effects (such as staictural changes in graphite tubes, surface porosity, analyte penetration into graphite etc.) ai e very important. 

This view is supported by our observation of hemi-spherically capped single-wall and multi-wall tubes on the same samples. It suggests that the Cf,o-derived tube could be the core of possible multilayer concentric graphitic tubes. After the single-shell tube has been... 

Fig. 10. TEM picture of a Ni metal left in the capillary of a graphite tube. Contact angle of the Ni particle on graphite surface (angle between the Ni/graphite interface and the Ni free surface) is larger than 90° (measured angle is about 140°), indicating poor wetting of Ni on the inner wall of a graphite tube.

Instead of employing the high temperature of a flame to bring about the production of atoms from the sample, it is possible in some cases to make use of either (a) non-flame methods involving the use of electrically heated graphite tubes or rods, or (b) vapour techniques. Procedures (a) and (b) both find applications in atomic absorption spectroscopy and in atomic fluorescence spectroscopy. 

The solution of the sample to be analysed (1-100 pL) is introduced by inserting the tip of a micropipette through a port in the outer (water) jacket, and into the gas inlet orifice in the centre of the graphite tube. The graphite cylinder is then heated by the passage of an electric current to a temperature... 

The sequence of events described above occurs at any given spot in a CVD flow reactor. As an example, one can consider the deposition of tungsten on the interior wall of a graphite tube by the hydrogen reduction of the fluoride as follows ... 

B - atomization efficiency, and volume of the cavity of the graphite tube (ml), provided that the analyte diffuses slowly out of the cavity (26). 

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. 

Asplla, K. I., Chakrabartl, C. L., and Bratzel, M. P., Jr. "Pyrolytic Graphite-Tube Micro-Furnace for Trace Analysis by Atomic Absorption Spectrometry". Anal. Chem. (1972),... 

Evenson, M. A. and Anderson, C. T., Jr. Ultramlcro Analysis for Copper, Cadmium and Zinc In Human Liver Tissue by Use of Atomic Absorption Spectrophotometry and the Heated Graphite Tube Atomizer". Clin. Chem. (1975), 2, 537-543. 

Evenson, M. A. and Pendergast, D. D. "Rapid Ultramicro Direct Determination of Erythrocyte Lead Concentration by Atomic Absorption Spectrophotometry with Use of a Graphite Tube Furnace". Clin. Chem. (1974), 20, 163-171. 

---