Quartz tube atomiser

GC-AAS has found late acceptance because of the relatively low sensitivity of the flame graphite furnaces have also been proposed as detectors. The quartz tube atomiser (QTA) [186], in particular the version heated with a hydrogen-oxygen flame (QF), is particularly effective [187] and is used nowadays almost exclusively for GC-AAS. The major problem associated with coupling of GC with AAS is the limited volume of measurement solution that can be injected on to the column (about 100 xL). Virtually no GC-AAS applications have been reported. As for GC-plasma source techniques for element-selective detection, GC-ICP-MS and GC-MIP-AES dominate for organometallic analysis and are complementary to PDA, FTIR and MS analysis for structural elucidation of unknowns. Only a few industrial laboratories are active in this field for the purpose of polymer/additive analysis. GC-AES is generally the most helpful for the identification of additives on the basis of elemental detection, but applications are limited mainly to tin compounds as PVC stabilisers. 

QTA Quartz tube atomiser SDME Static mercury drop electrode... 

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 ... 

The lifetime of the quartz tube atomiser is variable and can range up to several months. New tubes initially perform poorly and must be conditioned by several runs before achieving optimum sensitivity. Contamination of the quartz surface may result in significant signal suppression. As the electrothermal quartz furnace atomiser is comparatively robust and offers high overall efficiency and sensitivity at relatively low cost, it has found widespread application for the analysis of organo-metallic species of the elements Sn, Se, As, Sb, Pb, and Hg. 

QF Quartz tube flame atomiser chemiluminescence detector ... 

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. 

Air Mercury Dimethyl and methylmercuric chloride GC/quartz T tube atomiser 2-5 ng Bzezinska ef a/. (1983)... 

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. 

---