Graphite rod atomizer

J. "Determination of Copper In Serum With a Graphite Rod Atomizer for Atomic Absorption Spectrophotometry". Anal. Chlm. Acta (1971), 263-269. 

Reeves, R. D., Patel, B. M., Molnar, C. J., and Wlnefordner, J. D. "Decay of Atom Populations Following Graphite Rod Atomization In Atomic Absorption Spectrometry". Anal. Chem. 

Con rTtional flame photomeby requires pretreatment of biological samples vvhich is both tedioiis and time consuming. Moreover, atleast 2-3 ml of sample are required for a satisfactory analysis. This second requirement is a big drawback In blochemistiy where small samples are legion. Both the above problems have been solved with the development of graphite rod atomizer. 

Graphite rod atomizers do away with the requirement df a flame which has its own inconsistencies. Moreover they have an added advantage. If the sample to be analyzed is very dilute, repeated additions of it can be made to the cavity. Each of the aiquot is evaporated beforeafresh one is added.This concentrates the sample into the cavi Such dilute samples can then be analyzed easily. Another advantage is the )eed with which experiments can be performed. It takes roughly one minute per sample. 

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%. 

Graphite is planar, with the carbon atoms arranged in a hexagonal pattern. Each carbon atom is bonded to three others, two by single bonds, one by a double bond. The hybridization is sp2. The forces between adjacent layers in graphite are of the dispersion type and are quite weak. A lead pencil really contains a graphite rod, thin layers of which rub off onto the paper as you write (Figure 9.13, p. 242). 

Scientists identified the first carbon nanotubes in 1991. They sealed two graphite rods inside a container of helium gas and sent an electric discharge from one rod to the other. Much of one rod evaporated, but out of the inferno some amazing structures emerged (see illustrations). As well as the tiny 60-atom carbon spheres known as buckminsterfullerene—which had been known since 1985—long, hollow, perfectly straight carbon nanotubes were detected. 

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

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. 

In contrast, the coupling of electrochemical and spectroscopic techniques, e.g., electrodeposition of a metal followed by detection by atomic absorption spectrometry, has received limited attention. Wire filaments, graphite rods, pyrolytic graphite tubes, and hanging drop mercury electrodes have been tested [383-394] for electrochemical preconcentration of the analyte to be determined by atomic absorption spectroscopy. However, these ex situ preconcentration methods are often characterised by unavoidable irreproducibility, contaminations arising from handling of the support, and detection limits unsuitable for lead detection at sub-ppb levels. 

The thermal device used to elevate the temperature consists of a burner fed with a gaseous combustible mixture or, alternatively, in atomic absorption, by a small electric oven that contains a graphite rod resistor heated by the Joule effect. In the former, an aqueous solution of the sample is nebulised into the flame where atomisation takes place. In the latter, the sample is deposited on the graphite rod. In both methods, the atomic gas generated is located in the optical path of the instrument. 

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. 

Atomic Absorption Spectroscopy. One of the more sensitive instruments used to detect metal-containing toxicants is the AA spectrophotometer. Samples are vaporized either by aspiration into an acetylene flame or by carbon rod atomization in a graphite cup or tube (flameless AA). The atomic vapor formed contains free atoms of an element in their ground state, and when illuminated by a light source that radiates light of a... 

A — Anode, 1 — Platinum wire. 2 — Aluminium atom, < — Rubber lining, B — Cathode, 4 — Graphite rod, S — Diaphragm of asbestos cord. 

Atomic Absorption Spectroscopy. A titanium punch was used to cut 2.8-mm-diameter samples from the papers for calcium analysis. A Perkin-Elmer Model AD-2 Electronic Ultramicrobalance was used for the accurate weighing of the paper samples. Calcium content in the Dl-Ca waters and the papers was determined using a Varian Techtron AA-6 Spectrophotometer, with a Model 90 Carbon Rod Atomizer and Potentiometer A-25 Recorder (3). The solid samples (paper samples) were introduced into the graphite cup atomizer with tweezers. The standard solutions and Dl-Ca waters were inserted into the cup atomizer by means of 5-/xL Oxford pipet. 

The new, commercially available heated graphite ETA devices are available at much lower cost than XRF devices, and will certainly encourage expansion of the application of low total mass collection type studies. These heated graphite rods or furnaces are the type of ETA devices which one is most likely to encounter in general air pollution applications and most of this chapter s comments will be directed toward them however, the comments will also be pertinent to special purpose devices such as heated foil and wire atomizers. The reader is directed to Chapters 2 and 3 and to Siemer [9] for general descriptions of ETA devices, their applications, their characteristics and their limitations. Bancroft [10] has reviewed ETA applications to the ultratrace determination of metals. 

Recommended conditions for flame and approximate values for ETA (graphite rod, etc.) atomizers are given in Table 2 for a number of elements important with regard to air pollution studies. Conditions are included in the table for the flame system used when hydrides of arsenic, antimony and selenium are generated and passed through the flame. Burrel [16] discusses generation of metal hydrides and cold-vapor mercury evolution techniques in great detail. 

Fullerenes are large molecular carbon cages that are isolated by extraction of specially prepared soot with organic solvents such as benzene. A rich source of fiillerene is soot made by arcing graphite rods in a hehum atmosphere at 200 Torr pressure. The most coimnon fiiUerene is Ceo, which has a truncated icosahedral soccer ball stmcture with icosahedral (4) synunetry. Less synunetrical fiiUerenes with larger numbers of carbon atoms are known. C70 is the next most abundant after Ceo C76 and Cg4 are also known (see Carbon Fullerenes). 

A series of additional alterations of the graphite tube atomizer intended to improve performance (e.g. the cup and cup cuvette atomizer, boat and microboat platforms, carbon rods, graphite probes, ring chambers and surface atomizers) have also been reported [23]. Interested readers are referred to specific sources [2-7] for more details. 

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