Graphite atomic spectroscopy

G. Schlemmer and B. Radziuk, A Laboratory Guide to Graphite Furnace Analytical Atomic Spectroscopy, Springer-Verlag, Berlin (1998). 

Grobenski Z, Lehmann R, Radzuck B, Voellkopf U (1984) The determination of trace metals in seawater using Zeeman graphite furnace AAS. In Atomic Spectroscopy Application Study No. 686 (1984) Papers presented at Pittsburgh Conference, Atlantic City, NJ, USA... 

Reed E, Sauerhoff S, Piorier MC. Quantitation of platinum-DNA binding in human tissues following therapeutic levels of drug exposure—a novel use of graphite furnace spectrometry. Atomic Spectroscopy 1988 9 93-95. 

Autosamplers in chromatography and graphite furnace atomic spectroscopy, for example, have improved injection precision by a factor of 3-10 compared with that attained by humans. 

In atomic spectroscopy, analyte is atomized in a flame, an electrically heated furnace, or a plasma. Flames were used for decades, but they have been replaced by the inductively coupled plasma and the graphite furnace. We begin our discussion with flames because they are still common in teaching labs. 

Figure 21-6 An electrically heated graphite furnace for atomic spectroscopy (—38 mm long, in this case). [Courtesy Instrumentation Laboratory, Wiirrington, MA.]...

L vov platform Platform on which sample is placed in a graphite-rod furnace for atomic spectroscopy to prevent sample vaporization before the walls reach constant temperature. 

GFAAS = graphite furnace (flameless) atomic absorption spectroscopy MCAAS = micro-cup atomic spectroscopy DCOP-AES = direct current plasma-atomic emission spectroscopy HFP-AES = high frequency piasma-torch-atomic emission spectroscopy NAA - neutron activation analyst-, atomic absorption spectroscopy AAS - atomic absorption spectrophotometer XES = X-ray energy spectrometry and SEM - scanning electron microscopy. 

The methods of atomic spectroscopy, important in the first decades of the twentieth century, again played a significant role in the 1960s as a result of new inventions (Table 1.3). Development of atomic absorption, in particular with graphite furnace atomization, resulted in new procedures that could measure down to the 10 % level. Somewhat lower concentrations could be determined with generation of volatile compounds, in particular hydrides however, this was restricted to only a few elements. The development of atomization and excitation in... 

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... 

The number of applications of atomic techniques based on solid or slurry sampling is so large that only a comparatively minute fraction is discussed in this section. Interested readers are referred to the biannual reviews of Analytical Chemistry and the atomic spectroscopy update in the Journal of Analytical Atomic Spectrometry, among other sources, for more extensive information. A specific review of the uses of graphite atomizers modified with high-melting carbides has been published by Volynsky that includes virtually all metals determined in this manner [74]. 

An additional problem is that known elements in the periodic table, e.g. boron (B), tungsten (W) and molybdenum (Mo) tend to stick in the transport fine, nebuliser, spray chamber and torch causing memory effects in atomic spectroscopy. Elements that stick cause problems with quantification, and detection Emits and it is important that methods of reducing these are rigorously applied in analysis of these elements. However, memory effects in ICP-OES are not as pronounced as they are with graphite furnaces for refractory elements but they are present to some extent, and must be reduced or removed. 

The first requirement can be easily fulfilled by the preconcentration of the analyte before the analysis. Preconcentration has been applied to sample preparation for flame atomic absorption (25) and, more recently, for ICP (79,80) spectroscopy. However, preconcentration is not completely satisfactory, because of the increased analysis time (which may be critical in clinical analysis) and the increased chance of contamination or sample loss. Most important, however, a larger initial sample size is necessary. The apparent solution is a more sensitive technique. Table 2 lists concentrations of various metals in whole blood or serum (81,82) in comparison to limits of detection for the various atomic spectroscopy techniques. In many cases, especially for the toxic heavy metals, only flameless atomic absorption using a graphite furnace can provide the necessary sensitivity and accommodate a sample of only a few microliters (Table 1). The determination of therapeutic gold in urine and serum (83,84), chromium in serum (85), skin (86) and liver (87), copper in semen (88), arsenic in urine (89), manganese in animal tissues (90), and lead in blood (91) are but a few examples in analyses which have utilized the flameless atomic absorption technique. 

Butcher DJ (1998) Recent developments in graphite furnace atomic absorption spectrometry. In Sneddon J (ed.) Advances in Atomic Spectroscopy, vol. 4, p. 151. Greenwich, CT JAI Press. 

Figure 20-5 (a) Electrically heated graphite furnace for atomic spectroscopy. Sample is injected through the port at the top. LVov platform inside the furnace is heated by radiation from the outer wall. Platform is attached to the wall by one small connection hidden from view. [Courtesy Perkin-Elmer Corp., Norwalk, CT.] (b) Heating profile comparing analyte evaporation from wall and from platform. 

Graphite furnace applications are well-documented, though not as complete as flame AA. It has exceptional detection limit capabilities but with a limited analytical working range. Sample throughput is less than that of other atomic spectroscopy techniques. Operator skill requirements are much more extensive than for flame AA. 

The need for the determination of metallic constituents or impurities in pharmaceutical products has, historically, been addressed by ion chromatographic methods or various wet-bench methods (e.g. the USP heavy metals test). As the popularity of atomic spectroscopy has increased, and the equipment has become more affordable, spectroscopy-based techniques have been routinely employed to solve analytical problems in the pharmaceutical industry. Table 1 provides examples of metal determinations in pharmaceutical matrices, using spectroscopic techniques, and the reasons why these analyses are important. Flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry... 

Chang SB and Chakrabarti CL (1985) Factors affecting atomization in graphite furnace atomic absorption spectrometry. Progress in Analytical Atomic Spectroscopy 8 83-191. 

Holcombe JA and Rayson GD (1983) Analyte distribution and reactions within a graphite furnace atomizer. Progress in Analytical Atomic Spectroscopy 6 225-251. 

Professor B. V. L vov, the inventor of the very powerful analytical technique graphite furnace atomic absorption spectroscopy, has rightly pointed out in the Introduction of his definitive book entitled Atomic Absorption Spectrochemical Analysis that, The discovery of atomic absorption and the history of research into it are integral parts of the entire history of spectroscopy and spectrochemical analysis . Indeed, the early history of atomic spectroscopy, as far as spectrochemical analysis was concerned, consisted of the development of emission spectrochemical analysis, which was usually dependent on Fraunhofer lines (which are atomic absorption lines) for wavelength calibration. 

Analytical methods of atomic spectroscopy have been used in forestry and wood product research since their earliest development. Nowadays, almost all of the spectroscopic techniques available are employed in the analysis of metals and trace elements in diverse samples of industrial and environmental origin. The techniques that find most regular application include flame atomic absorption spectroscopy (F-AAS), graphite furnace atomic absorption spectroscopy (GF-AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and, occasionally, also direct current plasma atomic emission spectroscopy (DCP-AES). In many applications F-AAS is a sufficiently sensitive and precise technique however, in the analysis of some environmental samples for trace elements (forest soils, plant material and water) where concentrations may be very low (of the order of 100 ng mL" ) the greater sensitivity of GF-AAS and ICP/DCP-AES is required. In considering the applications of atomic spectroscopy to forestry and... 

A technique is any chemical or physical principle that can be used to study an analyte. Many techniques have been used to determine lead levels. For example, in graphite furnace atomic absorption spectroscopy lead is atomized, and the ability of the free atoms to absorb light is measured thus, both a chemical principle (atomization) and a physical principle (absorption of light) are used in this technique. Chapters 8-13 of this text cover techniques commonly used to analyze samples. 

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