Hydride generation-AAS

The procedure followed describes methods for the determination of total levels, and in certain cases, available amounts of trace elements in soils. The determination of arsenic in soil by hydride generation AAS is included. 

Method abbreviations D-AT-FAAS (derivative flame AAS with atom trapping), ETAAS (electrothermal AAS), GC (gas chromatography), HGAAS (hydride generation AAS), HR-ICP-MS (high resolution inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma atomic emission spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), TXRF (total reflection X-ray fluorescence spectrometry), Q-ICP-MS (quadrapole inductively coupled plasma mass spectrometry)... 

HG-AAS Hydride generation AAS HT-SEC, HTSEC High-temperature size-exclusion... 

The separation of mono-, di-, and tributyltin species in seawater by isocratic ion exchange liquid chromatography coupled to hydride generation AAS has been reported by Schulze and Lehmann [107]. Reported detection limits are 31,40, and 27 mol/1, respectively. 

An alternative to AAS for the end analysis of stannane generated by hydrogenation, could be collection in permanganate solution and spectrophotometric determination with phenylfluorone (3). This was applied to submicrogram Sn/L concentrations in fresh and marine waters276. Determination by hydride generation-AAS was found to be about 20 times more sensitive than by spectrophotometry of the phenylfluorone (3) complex28. 

B Manual Hydride Generation/AA Spectrometric Method (Arsenic and Selenium)... 

Hydride generation AAS is a well-established technique for the determination of selenium because of its selectivity and sensitivity. The detection limits are improved by concentrating the hydride prior to the transfer to the spectrometer. Cryogenic condensation in a U-tube at liquid nitrogen temperature is a preferred method of pre-concentration. However, selenium hydride is formed essentially only from Se. The selectivity for Se has been combined with various chemical preparation steps to determine the sum of SeIV and Se and the total selenium content of samples. Se concentrations are measured by the difference between the (Se + Se ) and Se contents. The difference between total selenium and (Se + Se ) contents represents the concentrations of Se° and Se2- species. These methods have been used for determinations of selenium species in natural waters. Soluble organic matter in some groundwater samples interferes with the hydride generation determination of selenium. Isolation of humic substances by their adsorption on resins has overcome this problem. 

In contrast to gas chromatographic separations, which require the preparation of volatile derivatives of tin compounds, separations carried out by means of HPLC do not necessarily require preparations of derivatives. HPLC has been used in conjunction with several detection techniques, including photometers, atomic absorption spectrometers and direct current plasma emission spectrometers after hydride generation. Some recent studies have involved fluorimetric detection (Kleibohmer and Cammann, 1989) and hydride generation AAS. The latter has been applied to the quantification of TBT in coastal water. 

Loska, K. and D. Wiechula. 2006. Comparison of sample digestion procedures for the determination of arsenic in bottom sediment using hydride generation AAS. Microchim. Acta 154 235-240. 

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... 

As species Zipex preconcentration, then separation on pellicular anion exchange resin Hydride generation AAS l-2ng [265]... 

Technique HG = hydride generation AAS = atomic absorption spectrometry GF = graphite furnace AES = atomic emission spectrometry MS = mass spectrometry AFS = atomic fluorescence spectrometry ASV = anodic stripping voltammetry SDDC = sodium diethyl dithiocarbamate. Procedures ISO = Memational Standards Organization ISO/CD = ISO Committee Draft SM = Standard Methods ... 

Fig. 3. Correlation between INAA and hydride generation - AAS for the Sb-determination...

The methods officially used in the wine trade transactions are summarized in Table 8.1. Generally, the OIV methods are officially adopted in the European Union without significant technical changes. The methods reported are mainly colorimetric, titrimetric, or use Atomic Emission Spectroscopy (AES, e.g. Flame Spectrophotometry), Atomic Absorption Spectroscopy (AAS), Hydride Generation-AAS (HG-AAS), Electrothermal-AAS (ET-AAS) and Vapour Atomic Flourescence Spectrophotometry (VAF). 

Yamamoto M., Yasuda M. and Yamamoto Y. (1985) Hydride generation AAS coupled with flow injection analysis, Anal Chem 57 1382-1385. 

Piwonka J., Kaiser G. and Tolg G. (1985) Determination of selenium at ng/g- and pg/g-levels by hydride generation-AAS in biotic materials, Fresenius Z Anal Chem 321 225-234. 

AAS techniques are commonly used for determination of selenium in environmental samples. Hydride generation AAS is more sensitive than flame or graphite furnace AAS for determination of selenium in materials of variable composition. Water samples, including freshwater, river water, sea water, and surface waters, and industrial wastes, muds, sediments, and soil samples have been analyzed by AAS techniques to detect selenium at parts-per-trillion levels (Bern 1981). Selenium(VI) and selenium(IV) can be distinguished in water samples with GFAAS by selective extraction procedures. HGAAS can also be used to distinguish between selenium(VI) and selenium(IV) in environmental samples because selenium(VI) does not readily form the hydride without reduction (Koirtyohann and Morris 1986). selenium(VI) is calculated on the basis of the total selenium minus selenium(IV) (Bern 1981). 

The direct GF-AAS-determination of selenium in urine is still under debate (Hoenig, 1991). Acid digestion is therefore recommended prior to hydride generation AAS or fluoromet-ric determinations. 

Hydride generation AAS (HGAAS) and cold vapour AAS (CVAAS) are special combinations of chemical separation and enrichment with AAS. In HGAAS the analyte is transformed to a volatile hydride, stripped off by an inert gas and atomized in a quartz tube, flame-in tube etc. About ten elements (As, Se, Bi, Sb etc.) can be determined by this technique. The accuracy and detection limits depend on the proper isolation of the hydride. CVAAS is the universally acknowledged most sensitive method for determination of Hg. The generation of elemental mercury vapour is similar to the hydride generation however the quartz cell may not be heated and this gives the name of the method. 

Selective sampling of organometallic compounds in air has already been mentioned. It is usually followed by hydride generation AAS or CT-GC-AAS measurements. 

---