Vapour generation atomic examples

Atomic fluorescence has the advantage of being less prone to spectral interferences than either AES or AAS. Molecular fluorescence is less of a problem than molecular absorption is in AAS. Scatter from the light source and quenching from the gaseous species in the atom cell are often the major sources of interference. For many applications where the analyte is separated from the matrix (e.g. vapour generation) chemical interferences may exist for example, the presence of high concentrations of some transition metals may interfere in the hydride formation process. This will inevitably lead to errors in the measurement unless preventative steps are taken. 

We have already seen in Chapter 2 that choice of atomizer system to be used may have a dramatic effect upon sensitivity, and thus upon signal-to-noise ratio. It is necessary to choose not only between flames, electrothermal atomization (ETA), and cold vapour and hydride generation techniques (which are discussed in Chapter 6), but sometimes also between different flames. Those elements which tend to form thermally stable oxides, such as Al, Ti, Si, Zr, may only be determined in a hotter, reducing nitrous oxide-acetylene flame. They cannot be determined with useful sensitivity in the air-acetylene flame. Some elements, Ba and Cr for example, may be determined in air-acetylene, but are more efficiently atomized in nitrous oxide-acetylene. 

Several different methods have been used successfully to generate a detectable concentration of short-lived free radicals inside the resonant cavity. The simplest method is a microwave discharge in the flowing gas, located upstream of the resonant cavity discharges in water vapour, for example, yield readily detectable concentrations of OH radicals. Shorter lived species have been produced by atom abstraction reactions inside the cavity, for example, by mixing fluorine atoms, produced by a microwave discharge in CF4, with a suitable secondary gas. Reaction of F atoms with OCS, for example, produces detectable concentrations of the SF radical [4],... 

The direct introduction of atomic vapour into the AAS flame can also be seen as an equipment variation [148, 152], Here, the evaporation of the steel samples can be carried out with the help of the glow-discharge lamp [148] or an aerosol generator with a low current d.c.-arc discharge [152]. Another example is the combination of gas chromatography and AAS [92], where AAS is used as an element detector. 

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