Spray chamber-burner assembly

The nebulizer is mounted in the spray-chamber burner assembly, as shown for the nitrous oxide or air-acetylene burner system (Fig. 32). Air or nitrous oxide are fed to the mixing chamber through the nebulizer. The combustion gas is fed directly to the burner. A self-aspirating concentric nebulizer is often used, but other types, including the Babington and cross-flow types (Section 21.4.1) are also applied. Nebulizers may be made of glass, corrosion-resistant metals such as Pt-Ir. or plastics such as Ryton. Sample solution consumption usually amounts to ca. S miymin in the case of gas flows of 1 -5 L/min. 

Flame atomization assembly equipped with spray chamber and slot burner. The inset shows the nebulizer assembly. 

Flame Sources Atomization and excitation in flame atomic emission is accomplished using the same nebulization and spray chamber assembly used in atomic absorption (see Figure 10.38). The burner head consists of single or multiple slots or a Meker-style burner. Older atomic emission instruments often used a total consumption burner in which the sample is drawn through a capillary tube and injected directly into the flame. 

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. 

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