Graphite furnace, temperature

R95031 Method 1638 Detennination of Trace Elements in Ambient Waters by Inductively Coupled Plasma-Mass Spectrometry 821R96005 Method 1638 Determination of Trace Elements in Ambient Waters by Inductively Coupled Plasma-Mass Spectrometry 821R96006 Method 1639 Determination of Trace Elements in Ambient Waters by Stabilized Temperature Graphite Furnace Atomic Absorption 821R96007 Method 1640 Determination of Trace Elements in Ambient Waters by On-Line Chelation Preconcentration and Inductively Coupled Plasma-Mass Spectrometry... 

Temperature Graphite Furnace AA Spectrometry Metals in Environmental Samples, Supplement 1 (EPA/600/R-94/111)... 

Determination of Trace Elements in Marine Waters by Stabilized Temperature Graphite Furnace Atomic Absorption... 

Baxter DC, Freeh W, Lundberg E. 1985. Determination of aluminum in biological materials by constant-temperature graphite furnace atomic-emission spectrometry. Analyst 110 475-482. 

In the plasma, the sample is vaporized and chemical bonds are effectively broken resulting in free atoms and ions. Temperatures of 5000-9000 K have been measured in the plasma compared to typical temperatures of 2000-3000 K in flames and graphite furnaces. 

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

Findlay, W. J., Zdrojewskl, A., and Qulckert, N. "Temperature Measurements of a Graphite Furnace Used In Flameless Atomic Absorption". Spectrosc. Lett. (1974), 7, 63-72. 

Electrical conductivity The electrical conductivity of refractories is important when they are used in electric furnaces. Except for graphite and metals, all other refractories are poor conductors of electricity. Graphite is a highly refractory material, and is used for electrodes and furnace linings in all high-temperature electric furnaces. Metals are not important as refractories in electric furnaces, but copper wires or busbars, for example, are utilized to carry current to the graphite electrodes. 

Theoretical treatments of graphite furnace atomic absorption spectrometry include a study of background signals due to sea salts [668], pyrometric measurement of furnace temperature [669], and methods of introducing the sample into the furnace [670]. 

The palladium and magnesium nitrates modifier has a substantial equalising effect on the atomisation temperature of the nine elements investigated. The optimum atomisation temperature for all but one element (thallium) is between 1900 and 2100 °C. This means that all elements can be determined at a compromise atomisation temperature of 2100 °C with a minimum sacrifice in sensitivity. Such uniform conditions for as many elements as possible are of vital importance if simultaneous multielement furnace techniques are envisaged. Moreover, in conventional graphite furnace AAS, uniform conditions for a number of elements can greatly facilitate and simplify daily routine analysis. 

The mechanism of stabilisation of the palladium and magnesium nitrates modifier was not investigated [749]. It is known, however, that palladium nitrate decomposes via the oxide to the metal at 870 °C, which melts at 1552 °C. The appearance temperature for palladium in a graphite furnace is around 1250 °C. As most of the investigated elements are stabilised to temperatures around 1200 °C, it can be assumed that the modifier acts by imbedding the analyte into the palladium matrix, or even by forming a kind of alloy with the analyte. 

Maximum power heating, the L vov platform, gas stop, the smallest possible temperature step between thermal pretreatment and atomisation, peak area integration, and matrix modification have been applied in order to eliminate or at least reduce interferences in graphite furnace AAS. With Zeeman effect background correction, much better correction is achieved, making method development and trace metal determinations in samples containing high salt concentrations much simpler or even possible at all. 

The graphite furnace system was originally developed by Andreae [712] when he found that the quartz cuvette gave only very poor sensitivity for germanium. This was attributed to the formation of GeO, a very stable diatomic species, at the relatively low temperatures of the quartz cuvette. At the higher temperatures available with the graphite furnace (2600 °C for the determination of Ge), a sensitivity could be obtained for germanium comparable to that of the other hydride elements. 

FIGURE 9.17 An illustration of a temperature program for a graphite furnace experiment (left), and the absorbance signal that results (right). The absorbance signal corresponds to the third temperature plateau. See text for a more detailed explanation. 

Describe the temperature program applied to a graphite furnace and explain each of the processes involved. 

The graphite furnace method of atomization utilizes a small graphite tube furnace to electrically heat rapidly a small volume of the analyte solution contained inside to a temperature that eventually causes atomization. 

Boron carbide is prepared by reduction of boric oxide either with carbon or with magnesium in presence of carbon in an electric furnace at a temperature above 1,400°C. When magnesium is used, the reaction may be carried out in a graphite furnace and the magnesium byproducts are removed by treatment with acid. 

Temperature distribution in (a) longitudinally and (b) transversely heated graphite furnace. 

Figure 14.9—Thermoelectric atomisation device, a) Graphite furnace heated by the Joule effect b) example of a graphite rod c) temperature program as a function of time showing the absorption signal. The first two steps of this temperature program are conducted under an inert atmosphere (argon scan).

Instruments that have burners and require nebulisation of dilute aqueous sample solutions generally have low background noise in the signal. With graphite furnaces, incomplete atomisation of the solid sample at elevated temperatures can produce interfering absorptions. This matrix effect does not exist in an isolated state and thus cannot be eliminated by comparison with a reference beam. This is notably the case for solutions containing particles in suspension, ions that cannot be readily reduced and organic molecules, all of which create a constant absorbance in the interval covered by the monochromator. 

Figure 14.16—Elements determined by AAS or FES. Most elements can be determined by atomic-absorption or flame emission using one of the available atomisation modes (burner, graphite furnace or hydride formation). Sensitivity varies enormously from one element to another. The representation above shows the elements in their periodic classification in order to show the wide use of these methods. Some of the lighter elements, C, N, O, F, etc. in the figure can be determined using a high temperature thermal source a plasma torch, in association with a spcctropholometric device (ICP-AbS) or a mass spectrometer (1CP-MS).

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