Hydride generation analytes

Numerous methods have been pubUshed for the determination of trace amounts of tellurium (33—42). Instmmental analytical methods (qv) used to determine trace amounts of tellurium include atomic absorption spectrometry, flame, graphite furnace, and hydride generation inductively coupled argon plasma optical emission spectrometry inductively coupled plasma mass spectrometry neutron activation analysis and spectrophotometry (see Mass spectrometry Spectroscopy, optical). Other instmmental methods include polarography, potentiometry, emission spectroscopy, x-ray diffraction, and x-ray fluorescence. 

The analytical response of inorganic and organic tin compounds of formula R SnX 4 was studied for direct hydride generation and measurement with a non-dispersive AFD (atomic fluorescense detector). Tributyltin and phenyltin compounds gave unsatisfactory results. This was corrected by warming the sample with a dilute Br2-HN03 solution37. 

Hydride generation Light absorbed by atoms derived from hydrides that are generated by chemical reaction are measured An excellent technique for a limited number of analytes that are difficult to measure otherwise... 

The hydride generation technique is a technique in which volatile metal hydrides are formed by chemical reaction of the analyte solutions with sodium borohydride. The hydrides are guided to the path of the light, heated to relatively low temperatures, and atomized. It is useful because it provides an improved method for arsenic, bismuth, germanium, lead, antimony, selenium, tin, and tellurium. 

Chemical separation techniques can be used to reduce spectral interferences and concentrate the analyte. These techniques include solvent extraction(39) and hydride generation(39, 46, 47). At Imperial College, the hydride generation technique is being used on a daily basis(46) for the analysis of soils, sediments, waters, herbage, and animal tissue. The solvent extraction technique is ideally suited for automated systems where the increased manipulation is carried out automatically, and a labor intensive step and sources of contamination are avoided. 

Hydride generator PS Analytical continuous flow hydride generator. 

Reductant A solution of 1% w/v sodium borohydride (NaBHJ should be freshly prepared in 0.1 M sodium hydroxide (NaOH), and placed in the reductant reagent compartment of the PS Analytical continuous flow hydride generator. 

Hydride generation for analytical use was introduced at the end of the 1960s using arsine formation (Marshal Reaction) in flame atomic absorption spectrometry (FAAS). A simple experimental setup for a hydride generator is shown in Figure 5.18. Today, hydride generation,91,92 which is the most widely utilized gas phase sample introduction system in ICP-MS, has been developed into... 

Analytical. Arsenic oxidation state determinations were per-formed by hydride generation-flame atomic absorption spectroscopy (AAS) at the University of Arizona Analytical Center. The analytical procedures are discussed in Brown, et al. (12). 

Basic techniques for speciation analysis are typically composed of a succession of analytical steps, e.g. extraction either with organic solvents (e.g. toluene, dichloromethane) or different acids (e.g. acetic or hydrochloric acid), derivatisa-tion procedures (e.g. hydride generation, Grignard reactions), separation (gas chromatography (GC) or high-performance liquid chromatography (HPLC)), and detection by a wide variety of methods, e.g. atomic absorption spectrometry (AAS), mass spectrometry (MS), flame photometric detection (FPD), electron capture detection (ECD), etc. Each of these steps includes specific sources of error which have to be evaluated. 

The determination of selenium species by HPLC coupled with detection by AAS has been described (Blais et al., 1991). Selenoniocholine and trimethyl-selenonium cations were separated chromatographically. The interface was described in Section 15.7. The process that occurred in the interface was called thermochemical hydride generation since the analytes were transformed to H2Se. The detection limits were 5-7 ng. The method was applied to the detection of the selenium species in human urine. Spiked samples were analysed satisfactorily. However, neither analyte was detected in several natural control samples. 

Valkirs, A.O., Seligman, PF., Olson, G.J., Brinckman, F.E., Matthias, C.L. and Bellama, J.M. (1987) Di- and tributyltin species in marine waters. Inter-laboratory comparison of two ultratrace analytical methods employing hydride generation and atomic absorption or flame photometric detection. Analyst, 112, 17-21. 

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... 

Aggett and Kadwani [13] employed a two stage single column anion exchange method using sodium hydrogen carbonate and chloride as eluate anions. These species appear to have no adverse effects in subsequent analytical procedures. Its successful application is dependent on careful control of pH. Analyses were performed by hydride generation atomic absorption spectroscopy... 

Several elements (including As, Bi, Ge, Pb, Sb, Se, Sn, and Te) form volatile hydrides when reacted with sodium borohydride at room temperature. By introducing the analyte as a volatile hydride, high-transport efficiencies, and therefore improved detection limits, can be achieved. Often as importantly, much of the sample matrix is not introduced into the ICP because those species do not form volatile compounds. Commercial hydride generation sample introduction systems are available. 

Selenium has also been investigated extensively with ICP-MS. It can be efficiently introduced into the plasma by hydride generation in order to improve detection limits. The analyte is efficiently transported into the plasma as a gas and the sample matrix is left behind. The hydride generator design can influence interferences and sensitivity [258]. Sample cross-contamination was eliminated when the air bubble normally entrained between samples was removed [258]. Isotope dilution can be used to obtain high accuracy. 

Magnuson et al. [105] described the use of CE with a hydrodynamically adjusted EOF with hydride generation for arsenic speciation and ICP-MS detection. Hydrodynamic pressure was applied in the opposite direction to the EOF so that large quantities of the analyte could be injected without significant peak broadening. Four arsenic species were separated with detection limits in the range 6-58 ppt. 

The most suitable techniques for the rapid, accurate determination of the elemental content of foods are based on analytical atomic spectrometry, for example, atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), and mass spectrometry, the most popular modes of which are Game (F), electrothermal atomization (ET), and hydride generation (HG) AAS, inductively coupled plasma (ICP), microwave-induced plasma (MIP), direct current plasma (DCP) AES, and ICP-MS. Challenges in the determination of elements in food include a wide range of concentrations, ranging from ng/g to percent levels, in an almost endless combination of analytes with matrix speci be matrices. 

Analyzer Q = quadrupole, CC = collision cell, DRC = dynamic reaction cell, MC = multicollector, SF = sector field. Analytical details CV = cold vapor, ETV = electro-thermal vaporization, FI = flow injection, HG = hydride generation, ID = isotope dilution, LA = laser ablation, UN = ultrasonic nebulization. Sample introduction in liquid or slurry (si) form. 

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