Arsine generator

Arsenic recoveries from the zinc column in the range 0.1-5pg ml-1 arsenic exceeded 97%. The concentrations at which certain elements interfere are shown in Table 12.16. Various other elements [A1 m, B m, Ca II, Cd II, Co II, Cr VI, Fe III, K I, Li I, Mg II, Mn H, Na I, Ni II, Pb II, S VI, Sn II and Zn II] showed no significant interference at the 500pg level. Only low senium concentrations in extracts can be tolerated. However, few environmental samples contain appreciable amounts of selenium. As selenium is not reduced to hydrogen selenide on the column, selenium will not interfere in the final determination step, but probably suppresses either arsenic reduction or arsine formation. Selenium appears to suppress arsine generation at high arsenic concentrations but causes a slight enhancement at low arsenic concentrations (around O.lpg), which could not be traced to arsenic impurities in the selenium standard used. 

Atsuya and Akatsuka [140] have described a method for determining trace amounts of arsenic. The technique, which uses capacitively coupled microwave plasma with an arsine generation system, has been used to determine arsenic in sewage sludge. 

Maher [13] has described a procedure for the determination of inorganic arsenic, monomethylarsenic and dimethylarsenic in marine organisms and estuarine sediments. The arsenic species are isolated by solvent extraction, separated by ion-exchange chromatography and selectively determined by arsine generation. Recoveries of spikes of 5 and lOpg of arsenic taken through the whole procedure were 92-96%. 

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 compounds MMA, DMA, and TMAO are reduced in acidic aqueous media by borohydride solutions to methylarsine (MeAsH2, bp 2°C), dimethylarsine (Me2AsH, bp 35°C), and trimethylarsine (Me3As, bp 55°C), respectively. These products are useful derivatives for speciation analysis of arsenic because they are readily separated from complex sample matrices and may be further separated from each other by distillation (41) or by gas chromatography (42) prior to their determination by element-specific detectors. Consequently, arsine generation techniques are the most commonly used methods for determining MMA, DMA, and TMAO in marine samples. 

S. brevicaulis (134). By the use of sensitive analytical methodology involving arsine generation, the arsenic intermediates proposed in Fig. 7 were identified in the growth medium. A significant result was the detection of TMAO, rather than trimethylarsine, as the major methylation product. The low concentrations of arsenic employed in these experiments resulted in TMAO being present at less than toxic concentrations, and further detoxification by reducing TMAO to the arsine was considered unnecessary. Whether or not TeMA was produced in these experiments is not known its presence was not reported, but it would not have been detected by the analytical technique used. 

Phase I of this project reviewed various processes to reduce, recycle and/or treat arsenic-laden wastes in a manner such that costs and disposal to the land are significantly reduced. The methods evaluated at various manufacturing stages included, buc were not limited to, separation, precipitation/fixation, ion exchange, and arsine generation. The information from Phase I was suitable for the design of a pilot scale treatment facility. 

Arsine Generation Soluble No Low Not Applicable Extreme High Minimal... 

Atallah, R.H. and D.A. Kalman. 1991.0n-line photo-oxidation for the determination of organoarsenic compounds by atomic-absorption spectrometry with continuous arsine generation. Talanta 38 167-173. 

Arsine has been determined colorimetrically or by collection on activated charcoal and flameless AAS analysis by S-229 (12). Nitric acid desorption of the charcoal offers a safe method of handling the arsenic analyte than arsine generation. This method does not specify use of an EDL as does S-309, however, it is advisable if an EDL source is available. 

Peter et al. [15] used an electrically heated quartz cell for the determination of arsenic in urine. Urine, 2 ml, was digested with 2 ml of nitric and perchloric acids (1 1). Aliquots of this solution were used for the subsequent arsine generation by sodium borohydride. The normal level of arsenic in urine was found to be less than lOppb. 

Two mefriods are described below. Acolorimetric method which is apphcable to blood, and an atomic absorption specfrophotometric method which is applicable to urine. Both methods employ mi arsine generating vessel. A iM ge volume of blood (up to 50 ml) or urine (25 ml or more) may be required because concentrations of arsenic in the body may be near the detection limits of the assays. 

Transfer 3 ml of the digested SMnple to tiie arsine generating vessel, add sufficient water to produce 35 ml, and then add 5 ml of hydrochloric acid, 2 ml of a 15% solution of potassiiun iodide, and 0.5 ml of Staimous Chloride Reagent (40%) swirl the solution, and allow to stand for 15 minutes. Insert a pad of glass wool moistened witii lead acetate solution into the lower tube of tiie generating vessel. Introduce 3 ml of the Silver DDC Solution into the absorber tube, and 3 g of grMiulated zinc into the flask. Mid immediately assemble the two parts of tiie apparatus. Allow tiie evolution of arsine to continue for 1 hour. Transfer the Silver DDC... 

Atomic Absorption Assay for Arsenic in Urine In this method, the arsine generator is suitably connected to the atomic absorption spectrophotometer. 

Terashima, S. Determination of arsenic in rocks, sediments and minerals by arsine generation and atomic absorption spectrometry. Anal Chim. Acta 86, 43-51 (1976). 

Fleming and Taylor described a method for the determination of total arsenic in organoarsenic compounds by arsine generation and atomic absorption spectrophotometry using a flame-heated silica furnace. Denyszyn and coworkers collected arsine at the 2 /rg/m level produced from organoarsine compounds, on charcoal, then desorbed the arsine in acid and analysed it by electrothermal atomic absorption spectrophotometry. Mean percentage recovery and standard deviation were, respectively, 89.1% and 0.10. 

Ricci and coworkers have described a highly sensitive, automated technique for the determination of MMAA, DMAA, p-aminophenyl arsonate, arsenite and arsenate. This procedure is based on ion-chromatography on a Dionex column, with 0.0024 M NaHC03/0.0019 M NajCOj/O.OOl M Na2B407 eluent, when all the compounds except arsenite and dimethyl arsinite are separated effectively. For separation of the last two, a lower ionic strength eluent (0.005 M Na2B407) can be used in a separate analysis. The detection system utilizes a continuous arsine generation system followed by heated quartz furnace atomization and atomic absorption spectrometry. Detection limits of less than 10 ng/ml were obtained for each species. 

Maher used ion-exchange chromatography to separate inorganic arsenic and methylated arsenic species in marine organisms and sediments. This procedure involves the use of solvent extraction to isolate the arsenic species, which are then separated by ion-exchange chromatography and determined by arsine generation. 

Arsenomolybdenum blue method was used to the determination of As after preliminary retention of the complexes of As(III) and ammonium diethyl dithiophosphate on a Ci8 sorbent [3]. The eluted complexes were merged with NaBH4 and the resulting solution was injected into the hydride generator/gas-liquid separator. The arsine generated was carried out by a stream of N2 and trapped in an alkaline iodine solution in which the colour reaction was developed. 

We have investigated the solvolytic stability and reactivity of polymer-bound borohydrides and have evaluated these materials in several applications such as solvent purification, arsine generation, and metal reduction. These polymer-bound borohydrides offer several advantages over sodium or tetraethylammonium borohydride. The primary advantages are the convenience of use and the minimal introduction of ionic species or organic by-products into the treated bulk media. With the polymer-bound borohydrides, the cation is bonded covalently to the insoluble resin while the borohydride anion or its oxidation product (borate) is retained by ionic bonding. Typically, boron at levels of less than 5 ppm is the only impurity introduced into the treated medium. 

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