Biological aspirating atomizers

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. 

The sample solution is aspirated into a toroidal shaped plasma, where atomization and excitation occurs. The emitted radiation is either measured simultaneously at previously selected atom lines, or one line after the other is sequentially scanned. The actual sensitivity depends on many parameters of the apparatus used, such as the type of nebulizer, optics, power, gas-flows, and observation height (for general review, see Broekaert and Tdig, 1987). If solvent extraction is applied as a technique for separation and preconcentration, however, it should be kept in mind that the plasma is easily distorted and extinguished by organic solvents. For thallium, there is some choice between different lines, but sensitivity is rather poor in any case, so that the direct application to decomposition solutions of rocks, soils, and biological samples is limited. 

For thallium, determinations at the 276.78 nm line with an acetylene/air flame are used throughout. Matrix problems are very low, but the sensitivity with regard to the low level of occurrence is poor. The sensitivity can be increased by mounting a slotted quartz tube on the burner head STAT = "slotted tube atom trap") (Milner, 1983), which leads to a detection limit of about 20 mg/kg in the solid sample, which is insufficient for the analysis of biological matrices. In MIBK extracts, determination of thallium is much more sensitive in flame AAS than in aqueous solutions (till about 7-fold). This can be used for solvent extraction of thallium from 0.1M HBr (Hubert and Chao, 1985), as xanthate at pH 8 (Aihara and Kiboku, 1980), or as iodide with tri-n-octylphosphinoxide into MIBK, and direct aspiration of the organic phase into the flame. 

Biological sample analysis by ICP-MS is not without problems. In biological samples, interferences from atomic and molecular ions produced in the plasma from argon and matrix constituents of the aspirated solutions plague the quantification of several elements,3- e.g. ai/i cI N/ cI NH, k/ SAtIH, CaJ Ar, As/ Ar Sci,... 

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