Electrothermal evaporation

There are several sample introduction methods that are used in conjunction with ICP, including nebulization, electrothermal evaporation, gas chromatography, hydride generation, and laser ablation [30]. Laser ablation combined with ICP (LA-ICP) is useful for analysis of solids. In such a source the sample is positioned in a chamber prior to the ICP source, the ablation cell. Argon gas at atmosperic pressure flows through the cell towards the ICP source. The sample is irradiated by a laser beam and... 

The direct determination of eight trace impurities (Na, Mg, Ca, V, Mn, Fe, Ni and Ga) in A1203 ceramic based powders by ICP-MS using electrothermal evaporation (ETV) with slurry sampling has been studied by Wende and Broekaert.66 The authors investigated the capability of several palladium group modifiers. Optimum results were obtained with the PdCl2 modifier... 

For special applications direct current plasma (DCP) (Leis et al., 1989) and micro-wave-induced plasma (MIP) may be used. The MIP first became widely used as a spectroscopic radiation source after a stable discharge at atmospheric pressure had been obtained (Beenakker, 1977 Beenakker et al., 1978). The MIP is not capable of taking up wet aerosols, but is useful for the excitation of dry aerosols, produced by electrothermal evaporation from a graphite furnace (Aziz et a ., 1982). Direct sample insertion has been discussed recently by Blain and Savin (1992). 

Electrothermal evaporation can be performed with dry solution residues, resulting from solvent evaporation, as well as with solids. In both cases the analyte evaporates and the vapor is kept inside the atomizer for a long time, from which it diffuses away. The high concentration of analyte in the atomizer results from a formation and a decay function. The formation function is related to the production of the vapor cloud. After matrix decomposition the elements are present in the furnace as salts (nitrates, sulfates, etc.). They dissociate into oxides as a result of the... 

When using electrothermal evaporation for sample introduction, the development of a suitable temperature program for the elements to be determined in a well-defined type of sample is of prime importance. In the case of liquid samples a small sample aliquot (10-50 pL) is brought into the electrothermal device with a syringe or with the aid of an automated sampler and several steps are performed. 

Direct solids sampling with electrothermal evaporation can be performed by dispensing an aliquot of a slurry prepared from the sample into the furnace. The analytical procedure is then completely analoguous with the one with solutions (see e.g. Ref. [181]). However, powders can also be sampled with special dispensers,... 

The development of the temperature program is a most important step in establishing a working procedure for any spectrometric method using electrothermal evaporation. It should be fully documented in all analytical procedures for the determination of a given series of elements in a well-defined type of sample. 

For powders, electrothermal evaporation may be used as most substances volatilize far below the volatilization temperature of graphite (>3600 °C). This approach is often hampered by the sample inhomogeneity, as it is generally a micromethod, as well as by anion effects causing chemical interferences [187]. Furthermore, transport losses can occur. 

Electrothermal evaporation and direct sample insertion This procedures allow the... 

In clinical analysis, Ca, Fe, Cu, Mg, Na and K can be determined directly even in microsized serum samples [128], Also electrothermal evaporation and direct sample insertion are particularly useful from this point of view. Generally, however, the power of detection of ICP-AES is too low for most analytical problems encountered in the life sciences. 

With electrothermal evaporation from a tungsten filament and quartz fiber optics, detection limits are at the 50-100 pg level for many elements, except for Fe which is subjected to spectral interferences from tungsten lines. This was established from the use of different working gases and especially from experiments with the addition of H2 to the argon. In the case of coupling with graphite furnace atomization Cu, Mg and Fe can be determined in serum samples without dilution for Fe and Cu and with a 1 100 fold dilution for Mg [434]. 

The MIP torch described by Jin et al. [456] (Fig. 104) allows operation with both argon and helium discharges and so the use of hydride generation or electrothermal evaporation is possible. The high excitation efficiency in the MIP torch (MPT) and the high robustness are understandable from the high electron tern-... 

Broekaert J. A. C. and Leis F. (1985) An application of electrothermal evaporation using direct solids sampling coupled with microwave induced plasma optical emission spectroscopy to elemental determinations in biological matrices, Mikrochim Acta II 261-272. 

Richts U., Broekaert J. A. C., Tschopel P. and Tolg G. (1991) Comparative study of a Beenakker cavity and a surfatron in combination with electrothermal evaporation from a tungsten coil for microwave plasma optical emission spectrometry (MIP-AES), Talanta 38 863-869. 

Wende M. C. and Broekaert J. A. C. (2001) Investigations on the use of chemical modifiers for the direct determination of trace impurities in AI2O3 ceramic powders by slurry electrothermal evaporation coupled to inductively coupled plasma... 

The best-known technique based on a combination of methods is ICP-MS. Here, the excited atoms are introduced upon their return to a lower energy level, through an interface into the ion source of a quadru-pole of a mass spectrometer. The ICP thus acts as an ion source and the mass spectrometer as the ion detector. The latest development in atomic spectrometry is the electrothermal evaporation-ICP-MS technique, where a graphite furnace is coupled to an ICP-MS. In this case, use is made of the most remarkable property of a graphite furnace (elimination of matrix interferences) by a graphite tube atomizer and subsequent transport of the atomic phase into the plasma and quadrupole. 

Before spectroscopic techniques can be applied to elemental analysis, the sample has to be atomized effectively. Thus, the commonly used atomization sources such as flames, electrothermal atomizers (e.g., filaments or graphite furnaces), and ICPs are also prerequisites for the laser-based techniques of atom spectrochemistry. In addition, atomization by LA or electrothermal evaporation in low-pressure gas atmospheres should also be considered. The atomization source must be optimized with regard to efficiency, stability, uniformity, and chemical interference in order to obtain the best analytical results. 

Thermal evaporation of analyte elements from the sample has long been used in atomic spectrometry. In 1940, Preuss [108] evaporated volatile elements from a geological sample in a tube furnace and transported the released vapors into an arc source. Thermal evaporation has also been used in double arc systems, where selective volatilization gives many advantages for direct solid analysis. Electrothermal evaporation became especially important with the work of L vov [3] and Massmann [4], who introduced electrothermally heated systems for the determination of trace elements in dry solution residues by atomic absorption spectrometry of the vapor cloud. 

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