Vapour generation atomic absorption spectrometry

In the past certain elements, e.g., antimony, arsenic, bismuth, germanium, lead, mercury, selenium, tellurium, and tin, were difficult to measure by direct AAS [3-9]. 

A novel technique of atomisation, known as vapour generation via generation of the metal hydride, has been evolved, which has increased the sensitivity and specificity enormously for these elements [5-7,9]. In these methods the hydride generator is linked to an atomic absorption spectrometer (flame graphite furnace) or inductively coupled plasma optical emission spectrometer (ICP-OES) or an inductively coupled plasma mass spectrometer (IPC-MS). Typical detection limits achievable by these techniques range from 3 pg/1 (arsenic) to 0.09 pgd (selenium). 

This technique makes use of the property that these elements exhibit, i.e., the formation of covalent, gaseous hydrides that are not stable at high temperatures. Antimony, arsenic, bismuth, selenium, tellurium, and tin (and to a lesser degree germanium and lead) are volatilised by the addition of a reducing agent like sodium tetrahydroborate(III) to an acidified solution. Mercury is reduced by stannous chloride to the atomic form in a similar manner. 

Automating the sodium tetrahydroborate system based on continuous flow principles represents the most reliable approach in the design of commercial instrumentation. Thompson and co-workers [10] described a simple system for multi-element analysis using an ICP spectrometer, based on the sodium tetrahydroborate approach. PS Analytical Ltd developed a reliable and robust commercial analytical hydride generator system, along similar lines, but using different pumping principles from those discussed by Thompson and co-workers [10]. 

A further major advantage of this range of instruments is that different chemical procedures can be operated in the instrument with little, if any, modification. Thus, in addition to using sodium tetrahydroborate as a reductant, stannous chloride can be used for the determination of mercury at very low levels. 

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G. Tao, S. N. Willie, R. E. Sturgeon, Determination of total mercury in biological tissues by Bow injection cold vapour generation atomic absorption spectrometry following tetramethylammonium hydroxide digestion, Analyst, 123 (1998), 1215D1218. 

F. Ubillus, A. Algeria, R. Barbera, R. Farre, M. J. Lagarda, Methylmercury and inorganic mercury determination in fish by cold vapour generation atomic absorption spectrometry, Food Chem., 71 (2000), 529-533. 

Vapour Generation Atomic Absorption Spectrometry (VGAAS)... 

Maintaining the quality of food is a far more complex problem than the quality assurance of non-food products. Analytical methods are an indispensable monitoring tool for controlling levels of substances essential for health and also of toxic substances, including heavy metals. The usual techniques for detecting elements in food are flame atomic absorption spectroscopy (FAAS), graphite furnace atomic absorption spectrometry (GF AAS), hydride generation atomic absorption spectrometry (HG AAS), cold vapour atomic absorption spectrometry (CV AAS), inductively coupled plasma atomic emission spectrometry (ICP AES), inductively coupled plasma mass spectrometry (ICP MS) and neutron activation analysis (NAA). 

CV-AAS, Cold Vapour Atomic Absorption Spectrometry ETA-AAS, Electrothermal Atomization Atomic Absorption Spectrometry FAAS, Flame Atomic Absorption Spectrometry FIG-AAS, Flydride Generation Atomic Absorption Spectrometry ICP-AES. Inductively Coupled Plasma Atomic Emission Spectrometry ID-MS, Isotopic Dilution Mass Spectrometry HR-ICP-MS, Magnetic Sector High Resolution Inductively Coupled Plasma Mass Spectrometry NAA, Neutron Activation Analysis Q-ICP-MS, Quadrupole Inductively Coupled Plasma Mass Spectrometry Z-ETA-AAS, Zeeman Electrothermal Atomization Atomic Absorption Spectrometry... 

Diemer, J. and Heumann, K.G. (1997) Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography. Fresenius J. Anal. Chem., 357,74-79. Duan, YX., Wu, M., Jin, Q.H. and Hieftje, G.M. (1995) Vapour generation of nonmetals coupled to microwave plasma-torch mass-spectrometry. Spectrochim. Acta B, 50,355-368. Ebdon, L., Hill, S. and Jones, R (1987) Interface system for directly coupled high performance liquid chromatography-flame atomic absorption spectrometry for trace metal determination./. Anal. At. Spectrom., 2, 205-210. 

Tsalev, D.L., M. Sperling, and B. Welz. 1992,On-line microwave sample pre-treatment for hydride generation and cold vapour atomic absorption spectrometry. Part 2. Chemistry and applications. Analyst 117 1735-1741. 

Lee SH, Jung KH, Lee DH. 1989. Determination of mercury in environmental samples by cold-vapour generation and atomic-absorption spectrometry with a gold-coated graphite furnace. Talanta 36(10) 999-1003. 

Hydride generation, as demonstrated by the determination of toxic arsenic species in human urine by cold-vapour atomic absorption spectrometry [148]. Two advanced oxidation processes relying on high-intensity focussed ultrasound were compared and ultrasound played an important role in both. Accurate results were reported. 

Initially hydride generation and cold vapour techniques were developed for the quantitative determination of the hydride-forming elements and mercury by atomic absorption spectrometry (Chapters, Sections 6.2 and 6.3), but nowadays these methods are also widely used in plasma atomic emission spectrometry. In the hydride generation technique, hydride-forming elements are more efficiently transported to the plasma than by conventional solution nebulization, and the production and excitation of free atoms and ions in the hot plasma is therefore more efficient. Spectral interferences are also reduced when the analyte is separated from the elements in the sample matrix. Both continuous (FIA) and batch approaches have been used for hydride generation. The continuous method is more frequently used in plasma AES than in AAS. Commercial hydride generation systems are available for various plasma spectrometers. 

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