Graphite atomizer

The wave function T i oo ( = 11 / = 0, w = 0) corresponds to a spherical electronic distribution around the nucleus and is an example of an s orbital. Solutions of other wave functions may be described in terms of p and d orbitals, atomic radii Half the closest distance of approach of atoms in the structure of the elements. This is easily defined for regular structures, e.g. close-packed metals, but is less easy to define in elements with irregular structures, e.g. As. The values may differ between allo-tropes (e.g. C-C 1 -54 A in diamond and 1 -42 A in planes of graphite). Atomic radii are very different from ionic and covalent radii. 

In this work, a method based on the reduction potential of ascorbic acid was developed for the sensitive detennination of trace of this compound. In this method ascorbic acid was added on the Cr(VI) solution to reduced that to Cr(III). Cr(III) produced in solution was quantitatively separated from the remainder of Cr(VI). The conditions were optimized for efficient extraction of Cr(III). The extracted Cr(III) was finally mineralized with nitric acid and sensitively analyzed by electro-thermal atomic absorption spectrometry. The determinations were carried out on a Varian AA-220 atomic absolution equipped with a GTA-110 graphite atomizer. The results obtained by this method were compared with those obtained by the other reported methods and it was cleared that the proposed method is more precise and able to determine the trace of ascorbic acid. Table shows the results obtained from the determination of ascorbic acid in two real samples by the proposed method and the spectrometric method based on reduction of Fe(III). 

Treatment for Graphite Atomization Systems". Anal. Chem. (1974), 2213-2215. 

Kantor, T., Clybum, S. A., and Velllon, C. "Contlnuoiis Sample Introduction with Graphite Atomization Systems for Atomic Absorption Spectrometry . Anal. Chem. (1974), 46, 2205-2213. 

Belsel, W. R. "The Direct Determination of Serum Chromium by an Atomic Absorption Spectrophotometer with a Heated Graphite Atomizer". Anal. Blochem. (1974), 283-292. 

Nowka R, Muller H (1997) Direct analysis of solid samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer and D2-background correction system (SS GF-AAS). Fresenius J Anal Chem 359 132-137. 

Using a newly developed, transversely heated graphite atomizer and D2-back-ground correction (for details see Sections 2.2 and 4.3), Cd, Pb and Cr were determined in cement and river sediment samples. Of the various calibration approaches applied the best results, also in comparison with wet chemical procedures, were achieved with calibration curves constructed by means of different BCR CRMs with different analyte concentrations and usually n = to individual intakes (Nowka and Muller 1997). 

Table 5.14. Application of Chelex-100 resin to the pre-concentration of metals in seawater prior to analysis by graphite atomic spectrometry ...

Organosilicon and organogermanium compounds were separated at 330-350 K on a Cromaton column coated with squalene. Improved quantitative determination was achieved by accumulation of preliminary decomposition products of the organometallic compounds in a graphite atomizer, followed by ETAAS32. 

HOPG highly oriented pyrolytic graphite atomically smooth ptanes)... 

Several types of atom cell have been used for AAS. Of these, the most popular is still the flame, although a significant amount of analytical work is performed using various electrically heated graphite atomizers. This second type of atom cell is dealt with at length in Chapter 3, and the material here is confined to flames. 

An investigation of both thermodynamic and kinetic considerations is necessary in the understanding of atomization in graphite atomizers. 

In a graphite atomizer, the atoms will appear according to a kinetic rate equation which will probably contain an exponential function. As the number of atoms in the atom cell increases, so does the rate of removal, until, at the absorption maximum (peak height measurement), the rate of formation equals the rate of removal. Thereafter, removal dominates. 

Instrumentation. A Varian Model 63 atomic absorption spectrophotometer, equipped with a graphite atomizer head was used to analyze all samples. Instrument parameters appear in Table I. A tin, hollow cathode lamp was used to generate the desired wavelength. A deuterium arc lamp was used to correct for non-atomic absorption signals. 

Note that these calculations of the heat of formation of methanol are not purely ab initio (quite apart from the empirical correction terms in the multistep high-accuracy methods), since they required experimental values of either the heat of atomization of graphite (atomization and formation methods) or the heat of formation of methane (formation method). The inclusion of experimental values makes the calculation of heat of formation with the aid of ab initio methods a semiempiri-cal procedure (do not confuse the term as used here with semiempirical programs... 

Unless a special type of autosampler can be used, micropipettes are an essential part of electrothermal atomisation techniques, as they give one of the most reliable methods of introducing small volumes of liquid samples into the graphite atomizer. 

The carbon atoms in Ceo are equivalent, and as expected only a single line is observed 5142.7 ppm (CeDe). C70 has Dih symmetry and as there are five distinct carbon atom environments, a five-line spectrum is observed 5150.1, 147.5, 146.8, 144.8, and 130.3 ppm (CeDe) of intensity ratio 10 20 10 20 10 (Figure 15). The initial assignments based on chemical intuition have been subsequently confirmed by 2D C NMR. The upheld line (5130.9 ppm) corresponds to the 10 graphitic atoms around the waist (type e), that he at the intersection of three six-membered rings. 

Many of the previous problems have been partly solved with the implementation of new instrument developments and improvements in analytical methodology over the past two decades. Progress in three different lines (viz. the design of graphite atomizers specially adapted for handling solid samples, the automation of solid sample insertion and the use of stable-temperature platform furnaces) has helped overcome some of the drawbacks of solid sampling with electrothermal atomizers and vaporizers. 

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]. 

A Perkin Elmer model 503 atomic absorption spectrophotometer, equipped with Perkin Elmer HGA-2100 heated graphite atomizer (Figure 2), a deuterium arc background corrector (12), and a strip chart recorder, was used. The HGA-2100 graphite furnace was purged with argon. Hollow cathode lamps were used except for cadmium for which an electrodeless discharge lamp (Perkin Elmer) was used. 

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