Hydride Generation Method

Eight elements including germanium, tin, lead, arsenic, antimony, bismuth, selenium, and tellurium form volatile, covalent hydrides (Table 14). Hydride generation can be employed both to separate these elements from the main 

Hydride generation methods involve three or four successive steps depending on the technique used (i) The hydride is generated by chemical reduction of the sample (ii) The formed hydride may be collected in the batch type methods (iii) The hydride is entrained in a gas stream into the atomizer (iv) The hydride is decomposed in the atomizer to form the atomic vapour, and the absorption signal is measured. A number of methods in use are based on this principle, but they differ in the means of reduction, atomization, and sample introduction. 

Some metals, for example, arsenic and selenium, are difficult to analyze by atomic absorption because their analytical wavelengths are subject to considerable interference. These metals, however, are readily converted to gaseous hydrides by treatment with strong reducing reagents such as sodium borohydride. Since the hydrides can be readily separated from the sample matrix, interferences are much reduced. A typical hydride generation AAS is 

Se(VI) is not readily reduced by sodium borohydride, and samples containing it must be prereduced. Samples containing organic selenium com- 

Samples of organic matter such as foods may be dry ashed before analysis. Magnesium oxide can be added as an ashing aid. The ashed sample is taken up in HC1 solution, and the oxidation state of the analyte is adjusted. For example, KI would be added to convert As(V) to As(III). Then a 3% NaBH4 solution in 0.5% NaOH is added and the hydride flushed into the instrument, AAS or ICP, for analysis. 

A1 Precipitate with 8-hydroxyquinoline, dissolve in acid for determination of hydroxyquinoline 590 

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This apparatus may also be adapted for what are termed hydride generation methods (which are strictly speaking flame-assisted methods). Elements such as arsenic, antimony, and selenium are difficult to analyse by flame A AS because it is difficult to reduce compounds of these elements (especially those in the higher oxidation states) to the gaseous atomic state. 

It should be noted that the hydride generation method may also be applied to the determination of other elements forming volatile covalent hydrides that are easily thermally dissociated. Thus, the hydride generation method has also been used for the determination of lead, bismuth, tin, and germanium. 

The use of the hydride generation method (Section 21.6) is far more sensitive for the determination of the listed elements. 

In summary, the hydride generation method cannot adequately differentiate between aquated SnIV and Sn11, which may coexist in certain, especially anaerobic, environments found in marine waters. Inorganic tin, speciated as tin (IV) , should probably be regarded as total reducible inorganic tin until more discriminatory techniques become available [578,580]. 

Cutter [18] has studied the application of the hydride generation method to the determination of selenium in saline waters. 

A standard UK hydride generation method [171] has been applied to the determination of selenium and arsenic in sludges and soils. 

Arsenic and selenium can be determined using the hydride generation method. These metals in HC1 medium can be converted to their hydrides by... 

At the present time there are no ETA—AAS methods that can compete with the cold vapour technique for Hg or with hydride generation methods for Sb and Te. Another attractive method for Sb and Te is low pressure microwave induced plasma (MIP) emission spectroscopy [138]. Using low-temperature ashing and solvent extraction as preparation, physiological concentrations of both elements ([Pg.376]

The ability to monitor trace levels of a number of heavy metals in a variety of samples is an important feature of modern environmental chemistry. Hence, sensitive analytical methods are required. When faced with the task of analyzing very low concentrations of antimony, bismuth and tin the hydride generation method is the first choice because of the improved sensitivity and lower detection limits as compared to many other techniques. The hydride generation technique includes the use of a reductant, such as a NaBH4 solution, to separate the volatile metal hydrides from the sample solution and the subsequent determination with atomic absorption after decomposition of the hydrides in a heated quartz cell. 

Acidification of water samples to a pH of 1.5 is recommended to preserve selenium compounds (Munoz Olivas et al. 1994). Nitric acid can be used, although it interferes with the hydride generation method of... 

Sodium borotetrahydride is now generally used as the reductant in various hydride generation methods. The reduction may be illustrated by the following reactions ... 

Two modes of operation can be applied for the hydride generation technique (i) In the normal batch system, the whole sample is reduced in a hydride generator and the hydride formed transported in a carrier gas stream to an absorption tube (ii) In the flow injection (FIA) technique all stages of the hydride generation method take place in a fully automated closed system. The FIA system is discussed in section 6.3. 

Spectral Interferences. The separation of the analyte from the matrix is a major advantage of the hydride generation method. The analyte passes into the atomizer as a gaseous hydride, while concomitants normally remain in the reaction vessel. Spectral interferences can virtually be excluded since a relatively small number of components are present in the atomizer. 

Continuous Hydride Generation. In the continuous or FIA hydride generation method the sample and reagent solutions are continuously pumped, usually by a multi-channel peristaltic pump, into a mixing chamber where... 

Hydride Generation Method. Hydrogen flames have been employed in AFS for the atomization of gaseous hydrides. These flames are very suitable for hydride generation methods because of the low background emission. 

S. Clark, J. Ashby, and PJ. Craig. On-colmnn hydride generation method for the production of volatile hydrides of tin, arsenic, and antimony for the gas chromatographic analysis of dilute solutions. The Analyst (London), 112, 1781 (1987). 

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