Electrothermal atomization process

Electrothermal Atomization The only gas that the electrothermal atomization process uses on a routine basis is high-purity argon, which costs 115 for a 340 fF (9630 L) cylinder. Typically, argon gas flows of np to 300 mL/min are required to keep an inert atmosphere in the graphite tube. At these flow rates, 540 h of use can be expected from one cylinder. Therefore, a typical laboratory running their instrument for 1000 h per year would consume almost two cylinders for 230. 

Atomization The most important difference between a spectrophotometer for atomic absorption and one for molecular absorption is the need to convert the analyte into a free atom. The process of converting an analyte in solid, liquid, or solution form to a free gaseous atom is called atomization. In most cases the sample containing the analyte undergoes some form of sample preparation that leaves the analyte in an organic or aqueous solution. For this reason, only the introduction of solution samples is considered in this text. Two general methods of atomization are used flame atomization and electrothermal atomization. A few elements are atomized using other methods. 

Figure 28-1 6 Block diagram of a single-beam atomic absorption spectrometer. Radiation from a line source is focused on the atomic vapor in a flame or an electrothermal atomizer. The attenuated source radiation then enters a monochromator, which isolates the line of interest. Next, the radiant power from the source, attenuated by absorption, is measured by the photomultiplier tube (PMT). The signal is then processed and directed to a computer system for output.

Peak area, peak height Properties of peak-shaped signals that can be used for quantitative analysis used in chromatography, electrothermal atomic absorption, and other techniques. Peptization A process in which a coagulated colloid returns to its dispersed state. 

The usefulness of the pre-electrolysis was stressed by Hori et al. They showed that the concentration of Fe " in KHCO3 solutions is remarkably decreased by die pre-electrolysis, as evidenced by Electrothermal Atomic Absorption Spectroscopy (ETAAS). Some papers report that deactivation still takes place even with solution treated with pre-electrolysis. Nevertheless, any analytical data has not been presented with regard to the electrolyte solutions. If any preelectrolysis is conducted in a cell, and the solution is transferred to another electrolysis cell, the solution is possibly contaminated during the transfer process. 

ETAAS. In ETAAS atomization takes place in an electrothermal atomizer which is heated to the appropriate temperature programme. The detection limits of the method are about two or three orders of magnitude better than FAAS. It is applicable to about 40 elements but generally for about 20 elements detection limits at the ng and pg level can be reached. Commensurable or better sensitivities have only INAA, ICP-MS and stripping voltammetry. Therefore ETAAS is widely used for environmental analysis. However the method suffers from serious interferences leading to systematic errors due to thermochemical processes in the atomizer. Background absorption is also a potential source for systematic errors. Spectral interferences are additive and cannot be corrected by the popular standard addition method. ETAAS is also not free of memory effects for refractory elements. 

Fast on-line/at process sulfur determination, 137 Filter furnace electrothermal atomic absorption spectrometry, 59 Fluoride, 232... 

The great sensitivity of electrothermal atomizers is due to their ability to atomize and retain a substantial portion of the analyte in the observation zone for a finite period of time. During the atomization process the rate of formation of the free atoms must be equal or greater than the rate of removal from the optical path ... 

Laser ablation has been investigated for MIP sample introduction with some success. The advantage of this technique is that, as with electrothermal atom-izaton, a two-step process is used. The laser is used to volatilize and atomize the sample before it is introduced into the plasma for excitation, thus overcoming any problems with low thermal temperatures in the MIP. The sample is transferred from the laser ablation cell to the plasma via a carrier gas that is usually the support gas. The main problem with laser ablation is lack of precision due to the shot-to-shot variation in laser power and its nonlinear effect on the ablation process. To overcome this several different normalization techniques have been investigated. 

The heating of the sample in the electrothermal atomizer is programmable to fit the variety of sample types and analytes. The atomization process involves the following steps ... 

T. G. Kazi, N. Jalbani, J. A. Baig, G. A. Kandhro, H. I. Afridi, M. B. Arain, M. K. Jamali and A. Q. Shah, Assessment of toxic metals in raw and processed milk samples using electrothermal atomic absorption spectrometer. Food Chem. Toxicol, 2009, 47(9), 2163-2169. 

Electrothermal atomization (ETA) for use with atomic absorption (AA) has proved to be a very sensitive technique for trace element analysis over the last three decades. However, the possibility of using the atomization/heating device for electrothermal vaporization (ETV) sample introduction into an ICP mass spectrometer was identified in the late 1980s. The ETV sampling process relies on the basic principle that a carbon furnace or metal filament can be used to thermally separate the analytes... 

The actual atom production and dissipation processes in electrothermal atomizer are much more complex than that described above. In many cases the analyte is atomized as a result of a set of multistage processes taking place simultaneously. The basic processes that occur with analyte in a graphite furnace are shown schematically in Figure 3 and listed in Table 1. The last column of the Table shows the elements for which the respective processes have been documented. 

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.

Chakrabarti CL, Gilmutdinov AKh and Hutton JC (1993). Digital imaging of atomization processes in electrothermal atomizer for atomic absorption spectrometry. Analytical Chemistry 65 716-723. 

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