Atomic quartz tube atomiser

The most widely used atomiser for hydride generation is the heated quartz T-tube atomiser with a typical diameter of 10 mm and a length of 100—150 mm, making it compatible with the optical path of most AA spectrometers. The quartz tube is electrically heated to 700—1000 °C which permits one to optimise the atomisation temperature for each element. The quartz tube may either have open ends, or these ends are sealed by removable quartz windows, and holes at the extreme ends of the quartz tube provide the gas flow outlets. This set-up increases the residence time of the atoms in the light path and thus improves sensitivity. With continued use the performance of the quartz tube atomiser invariably deteriorates in terms of sensitivity and precision. This is attributed both to devitrification of the inner surface of the quartz tube to a less inert modification, and to contamination of the inner atomiser surface by deposition of small particles and droplets that were not efficiently removed by the gas—liquid phase separator. 

The decomposition of hydrides to form free atoms is mainly due to the reaction with hydrogen radicals, but oxygen also plays an active role. The following reactions may take place within a quartz tube atomiser ... 

Lee [524] described a method for the determination of nanogram or sub-nan ogram amounts of nickel in seawater. Dissolved nickel is reduced by sodium borohydride to its elemental form, which combines with carbon monoxide to form nickel carbonyl. The nickel carbonyl is stripped from solution by a helium-carbon monoxide mixed gas stream, collected in a liquid nitrogen trap, and atomised in a quartz tube burner of an atomic absorption spectrophotometer. The sensitivity of the method is 0.05 ng of nickel. The precision for 3 ng nickel is about 4%. No interference by other elements is encountered in this technique. 

Instead of flames, atomic absorption spectrometers sometimes employ graphite furnaces or (relatively speaking) cold quartz tubes as atomisers these devices are not normally required for the purpose of qualitative analysis (unless the volume of sample available is very small), and will not be discussed here. 

The concentration of the hydrogen radical in the atomiser tube is several orders of magnitude higher than that of the hydroxyl radical. Thus if a metal hydride is introduced into the quartz tube, it wiU undergo the following subsequent reactions, leaving finally the free atom in the gas phase ... 

Since mercury is present already in the atomic state in the cold vapor technique, there is no need for an atomiser as such. The sample vapor is swept directly from the reduction cell or the amalgamation trap in the carrier gas stream to a 10 cm length T-shaped quartz tube that is moderately heated (to ca. 200 °C to prevent condensation of mercury). This quartz cell is located in the light path of a conventional AA spectrometer where the attenuation of a characteristic Hg line source is measured. Dedicated AA spectrometers (which, in this case, often have a continuum light source) may also be used with longer absorption cells (300 mm pathlength) to increase the sensitivity. 

Quartz tube (QT) atomisation and high-resolution continuum source hydride generation atomic absorption spectrometry (FIR-CS HG-AAS) were used to determine lead. A full two-level factorial design characterised the effects of the reagent concentrations. The experimental conditions were determined using a Box-Behnken design. 

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