Arsenic complex hydrides

In covalent hydrides, hydrogen and the metal are linked by a covalent bond. Aluminum, silicon, germaninm, arsenic, and tin are some of the metals whose covalent hydride structures have been stndied extensively. Some ionic hydrides, snch as LiH or MgH2, exhibit partial covalent character. The complex hydrides, such as lithium aluminum hydride and sodium borohydride, contain two different metal atoms, usually an alkali metal cation bound to a complex hydrido anion. The general formula for these compounds is M(M H4) , where the tetrahedral M H4 contains a group IIIA metal such as boron. 

C. Helling, V. Imhof, L. Nielsen, and E. Jacobson Complex Alumino-Hydrides containing Nitrogen, Phosphorus and Arsenic. Inorg. Chem. 2, 504 (1963). 

The most useful chemical species in the analysis of arsenic is the volatile hydride, namely arsine (AsH3, bp -55°C). Analytical methods based on the formation of volatile arsines are generally referred to as hydride, or arsine, generation techniques. Arsenite is readily reduced to arsine, which is easily separated from complex sample matrices before its detection, usually by atomic absorption spectrometry (33). A solution of sodium borohydride is the most commonly used reductant. Because arsenate does not form a hydride directly, arsenite can be analyzed selectively in its presence (34). Specific analysis of As(III) in the presence of As(V) can also be effected by selective extraction methods (35). 

The EPA has approved special methods for arsenic (EPA Method 7061) and selenium (EPA Method 7741) analysis by gaseous hydride generation technique, which offer a unique combination of selectivity and sensitivity. This technique has an advantage of being able to isolate these elements from complex matrices that may cause interferences in analysis with other techniques. 

A combination of IPC and inductively coupled plasma (ICP) MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [108-118] because it provides specific and sensitive element detection. Selenium IPC speciation was joined to atomic fluorescent spectrometry via an interface in which all selenium species were reduced by thiourea before conventional hydride generation [119], Coupling IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes with cold vapor generation and atomic fluorescence detection was successfully validated [120]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of Cr(III) and Cr(VI) [121] and arsenic compounds employing hydride generation [122]. 

IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes, coupled to cold vapor generation and atomic fluorescence detection, was successfully validated [18]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of arsenic compounds employing hydride generation [17]. In the analytical speciation of chromium using in... 

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