Graphite-furnace atomizers carbon

Figure 15-12 is a schematic illustration of a technique known as acid volatile sulfides/ simultaneously extracted metals analysis (AVS/SEM). Briefly, a strong acid is added to a sediment sample to release the sediment-associated sulfides, acid volatile sulfides, which are analyzed by a cold-acid purge-and-trap technique (e.g., Allen et ai, 1993). The assumption shown in Fig. 15-12 is that the sulfides are present in the sediments in the form of either FeS or MeS (a metal sulfide). In a parallel analysis, metals simultaneously released with the sulfides (the simultaneously extracted metals) are also quantified, for example, by graphite furnace atomic absorption spectrometry. Metals released during the acid attack are considered to be associated with the phases operationally defined as "exchangeable," "carbonate," "Fe and Mn oxides," "FeS," and "MeS."... 

A limited amount of work has been carried out on the determination of molybdenum in seawater by AAS [107-109] and graphite furnace atomic absorption spectrometry [110]. In a recommended procedure a 50 ml sample at pH 2.5 is preconcentrated on a column of 0.5 gp-aminobenzylcellulose, then the column is left in contact with 1 mol/1 ammonium carbonate for 3 h, after which three 5 ml fractions are collected. Finally, molybdenum is determined by AAS at 312.2 nm with use of the hot-graphite-rod technique. At the 10 mg/1 level the standard deviation was 0.13 xg. 

Chemistry (Brown et al. 1981). Direct aspiration into a flame and atomization in an electrically heated graphite furnace or carbon rod are the two variants of atomic absorption. The latter is sometimes referred to as electrothermal AAS. Typical detection limits for electrothermal AAS are <0.3 pg/L, while the limit for flame AAS and ICP-AES is 3. 0 pg/L (Stoeppler 1984). The precision of analytical techniques for elemental determinations in blood, muscles, and various biological materials has been investigated (Iyengar 1989). Good precision was obtained with flame AAS after preconcentration and separation, electrothermal AAS, and ICP-AES. 

Beinrohr, E., Lee, M.L., Tschopel, P., Tolg, G. Determination of platinum in biotic and environmental samples by graphite furnace atomic absorption spectrometry after its electrodeposition into a graphite tube packed with reticulated vitreous carbon. Fresenius J. Anal. Chem. 346, 689-692 (1993)... 

The three universal extractants, ammonium carbonate, ammonium acetate, and AB-DTPA, have an advantage in that the extracts can be read directly for their Mo concentrations by graphite-furnace atomic-absorption spectrometry, direct-current plasma-emission spectrometry. 

This technique uses an electrothermally heated graphite furnace, a carbon rod, or metal filament to atomize the sample. The sample is placed in the form of a solution or a solid in the atomizer. 

Researchers have developed other types of ETAs over the years, including filaments, rods, and ribbons of carbon, tantalum, tungsten, and other materials, but the only commercial ETA available is the graphite furnace atomizer. 

Some of the physical and chemical constraints on the flame atomization process — which usually precluded application to solid samples — were overcome with the advent of flameless atomization, initially accomplished with the pyrolytic coated graphite tube (or carbon rod-type) furnace atomizer. The graphite tube is a confined furnace chamber where pulsed vaporization and subsequent atomization of the sample is achieved by raising the temperature with a programmed sequence of electrical power. A dense population of ground state atoms is produced as a result for an extended interval in relation to the low atom density and short residence time of the flame. The earliest use of furnace devices in analytical atomic spectroscopy is credited to a simultaneous development by Lvov [15] and Massmann [16] however, the first application of one such device to a... 

In flameless AA techniques (carbon rod or graphite furnace ), the sample is placed in a depression on a carbon rod in an enclosed chamber. Strips of tantalum or platinum metal may also be used as sample cups. In successive steps, the temperature of the rod is raised to dry, char, and finally atomize the sample into the chamber. The atomized element then absorbs energy from the corresponding hollow-cathode... 

Atomic absorption spectrometry, belonging to a class of techniques also defined as optical atomic spectrometry, has been for some four decades - and continues to be - one of the most important, dominant determinative techniques. It includes flame atomic absorption spectrometry (FAAS), electrothermal atomization atomic absorption spectrometry (ETAAS) (including graphite furnace AAS (GFAAS), carbon rod AAS, tantalum strip AAS), and gaseous generation (cold vapor AAS for Hg, hydride gener-... 

Related to the carbon rod atomizer is the heated graphite tube furnace atomizer. Here, the sample is injected into the center of a graphite tube, which is resistively heated. Welz (W1) reported the determination of blood lead with such a system in which the sample is dried (20 seconds), ashed, and atomized by stepwise increase in the temperature. The precision was poor, though, being 5-10 /xg/100 ml. Norval and Butler (N3) described a graphite tube system for use on any number of atomic... 

Atomization. Atomization in the graphite furnace can emanate from either molecules or atoms depending on the nature of the sample and behaviour of the analyte. If atomization emanates from molecules, it can be a thermal decomposition or dissociation of a compound, or the reduction of a metal oxide on the hot graphite surface. The difference between these two mechanisms is the active participation of the cuvette material (carbon) in the dissociation of the sample molecules. If atomization emanates from the metal, it can be classified either as desorption or volatilization. 

Several different electrothermal atomizers such as carbon rod, graphite ribbon, graphite furnace, and metal loop atomizers, have been designed for AFS measurements. In general, the electrothermal atomization method is time-consuming and expensive with respect to flame atomization. It is, thus, appropriate to use electrothermal atomization only when the sample amount or analyte concentration restrict the use of flames or plasmas. 

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