Atomic absorption spectrometry burners

For flame emission measurements, burners of the Meker type with a circular orifice covered by a grille are used whereas in atomic absorption spectrometry, a slit burner is preferred. In both cases, the flame consists of two principal zones or cones (Figure 8.21(b)). The inner cone or primary... 

Flame atomic absorption spectrometry can be used to determine trace levels of analyte in a wide range of sample types, with the proviso that the sample is first brought into solution. The methods described in Section 1.6 are all applicable to FAAS. Chemical interferences and ionization suppression cause the greatest problems, and steps must be taken to reduce these (e.g. the analysis of sea-water, refractory geological samples or metals). The analysis of oils and organic solvents is relatively easy since these samples actually provide fuel for the flame however, build-up of carbon in the burner slot must be avoided. Most biological samples can be analysed with ease provided that an appropriate digestion method is used which avoids analyte losses. 

Figure 2.5 Nebuliser and burner (after M. Pinta. Atomic Absorption Spectrometry. Applications for Chemical Analysis, volume 1, 2nd edition. Masson et Cie. Paris. 1979).

Flame atomic absorption spectrometry (FAAS) is used primarily for liquids. The sample is converted into an aerosol by the nebuliser, atomised to free atoms, mixed with the combustible gases and ignited in the flame, which can rise to a temperature of 2600 °C. A long burner is used to increase the pathlength. The most commonly used flames are air-acetylene and nitrous oxide-acetylene mixtures. 

New flameless methods for sample presentation to the instrument, like the graphite rod and the. tantalum boat, are expanding the use and applications of atomic absorption spectrometry. In the first technique the burner is replaced by a graphite rod with a small well where a few microliters of sample are deposited and electrically heated by means of controlled power supply. Important advantages of this procedure are that a very small sample is needed and the dilution of viscous samples is not required. 

As is also the case in atomic absorption spectrometry, the sample must enter the burner via an atomizer in ICP as well. The efficiency of the atomizer plays a considerable role in producing as finely distributed an aerosol as possible. For example, the Meinhardt atomizer, a concentric pneumatic glass atomizer with fixed capillaries, is often used. The quantity of carrier gas and the efficiency of the atomizer have in the meantime been well matched for ICP analysis. The cross-flow atomizer similarly works on pneumatic principles. The two capillaries used are adjustable and can be... 

In the premix burner, the sample, in solution form, is first aspirated into a nebulizer where it forms an aerosol or spray. An impact bead or flow spoiler is used to break the droplets from the nebulizer into even smaller droplets. Larger droplets coalesce on the sides of the spray chamber and drain away. Smaller droplets and vapor are swept into the base of the flame in the form of a cloud. An important feature of this burner is that only a small portion (about 5%) of the aspirated sample reaches the flame. The droplets that reach the flame are, however, very small and easily decomposed. This results in an efficient atomization of the sample in the flame. The high atomization efficiency leads to increased emission intensity and increased analytical sensitivity compared with other burner designs. The process that occurs in the burner assembly and flame is outlined in Table 7.2. This process is identical to the atomization process for atomic absorption spectrometry (AAS), but now, we want the atoms to progress beyond ground-state free atoms to the excited state. 

Fig. 82. Burner-nebulizer assembly for flame atomic absorption spectrometry, a Burner head with mixing chamber b nebulizer c impactor bead d impact surfaces e nebulizer socket. (Courtesy of Bodenseewerk PerkinElmer, Oberlingen.)...

Figure 32. Burner-nebulizer assembly for flame atomic absorption spectrometry...

Flame Atomic Absorption Spectrometry. It is usually considered that about 95% of the observed problems are related to the light system, the nebuliser/ burner and the instrument cleanliness the instrument s optics and electronics rarely fail. For example, most commonly problems accounting for absorbance lower than expected are related to ... 

McCorriston, L. L., Ritchie, R. K., Determination of Lead in Gasoline by Atomic Absorption Spectrometry Using a Total Consumption Burner, Anal. Chem. 47 [1975] 1137/9. 

Atomic fluorescence spectrometry has a number of potential advantages when compared to atomic absorption. The most important is the relative case with which several elements can be determined simultaneously. This arises from the non-directional nature of fluorescence emission, which enables separate hollow-cathode lamps or a continuum source providing suitable primary radiation to be grouped around a circular burner with one or more detectors. 

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