Antimony hydride methods

The recommended procedure for the determination of arsenic and antimony involves the addition of 1 g of potassium iodide and 1 g of ascorbic acid to a sample of 20 ml of concentrated hydrochloric acid. This solution should be kept at room temperature for at least five hours before initiation of the programmed MH 5-1 hydride generation system, i.e., before addition of ice-cold 10% sodium borohydride and 5% sodium hydroxide. In the hydride generation technique the evolved metal hydrides are decomposed in a heated quartz cell prior to determination by atomic absorption spectrometry. The hydride method offers improved sensitivity and lower detection limits compared to graphite furnace atomic absorption spectrometry. However, the most important advantage of hydride-generating techniques is the prevention of matrix interference, which is usually very important in the 200 nm area. 

Pretorius L, Kempster PL, van Vliet HR, et al. 1992. Simultaneous determination of arsenic, selenium and antimony in water by inductively coupled plasma hydride method. F J Anal Chem 342(4-5) 391-393. 

To summarise, FAAS is very easy to use. Interferences are known and can be controlled. Extensive application information is also readily available. Its precision makes it an excellent technique for the determination of a number of commonly analysed elements at higher concentration in polluted soil samples. Its main drawback is its speed in relation to multi-element techniques such as ICP-AES and ICP-MS. Where direct-aspiration flame atomic absorption technique does not provide adequate sensitivity, reference is made to specialised techniques (in addition to graphite furnace procedure) such as the gaseous-hydride method for arsenic, antimony and selenium and the cold-vapour technique for mercury. 

Stibine, Antimony hydride. HjSb mol wt 124.78. H 2 42%.. Sb 97.57%.. SbH,. Conveniently prepd by dissolving zinc-antimony or magaesium -antimony alloy in dil HC1 Hurd, Chemistry of the Hydrides (Wiley. New York, 1952) p 132. Detailed directions (including prepn of the alloy from powdered Sb and Mg) Schenk in Handbook of Preparative Inorganic Chemistry voL 1, O. Brauer, Ed. (Academic Press, New York. 2nd ed.. 1963) pp 606-608. Review of preparative methods Jolly, Norman, Hydrides of Groups IV and V in Preparative Inorganic Reactions vnl. 4, W. L. Jolty, Ed. (Interscience, New York, 1968) pp 1 -58. 

The elemental analyses were carried out at various laboratories with different analytical techniques. Copper and zinc were analyzed by ICP with a Varian Liberty 220 instrument at the Enel S.p.A. laboratories of Larderello (PI). Antimony, mercury and arsenic were determined in our laboratories with a Perkin-Elmer 5000 AAS equipped with FIAS using the hydride method. Lead and cadmium were analyzed at the Enel S.p.A. laboratories of Piacenza with a Perkin-Elmer Elan 5000 ICP-MS equipped with two mass flow controllers and a Perkin-Elmer Gem-Tip crossflow nebulizer. To enhance the sensitivity for cadmium, we also employed a CETAC U5000AT ultrasonic nebulizer (Cetac Technologies Inc., Omaha, NE) as an alternative introduction system to the pneumatic nebulizer. 

M is the analyte and m may be equal to n or not (for example, As and As are both reduced to AsHs). Hydrides were collected in U-tubes in a nitrogen trap or in rubber balloons. Titanium(iii) chloride—hydrochloric acid and magnesium-zinc reductants were used to extend the hydride method to bismuth, antimony, and tellurium. For some elements, especially tin, lead, and tellurium, the hydride formation reaction is relatively slow and hence the collection vessel is necessary. In addition, arsenic(v) must be reduced to arsenic(iii) by tin(ii) chloride or potassium iodide before the actual hydride generation when a metal-acid reduction is employed. 

On account of the complexity of the matrix the hydride method of AAS [64] is used for the determination of Sb in biological materials. This means that Ul-valent antimony yields an appreciably greater measurement signal than V-valent. Hence, if determination of total antimony is adequate, the first step is to convert any V-valent antimony to the Hi-valent state. 

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. 

Although electrothermal atomisation methods can be applied to the determination of arsenic, antimony, and selenium, the alternative approach of hydride generation is often preferred. Compounds of the above three elements may be converted to their volatile hydrides by the use of sodium borohydride as reducing agent. The hydride can then be dissociated into an atomic vapour by the relatively moderate temperatures of an argon-hydrogen flame. 

Sturgeon et al. [59] have described a hydride generation atomic absorption spectrometry method for the determination of antimony in seawater. The method uses formation of stibene using sodium borohydride. Stibine gas was trapped on the surface of a pyrolytic graphite coated tube at 250 °C and antimony determined by atomic absorption spectrometry. An absolute detection limit of 0.2 ng was obtained and a concentration detection limit of 0.04 pg/1 obtained for 5 ml sample volumes. 

Tao et al. [658] have described a procedure in which antimony and arsenic were generated as hydrides and irradiated with ultraviolet light. The broad continuous emission bands were observed in the ranges about 240-750 nm and 220 - 720 nm, and the detection limits were 0.6 ng and 9.0 ng for antimony and arsenic, respectively. Some characteristics of the photoluminescence phenomenon were made clear from spectroscopic observations. The method was successfully applied to the determination of antimony in river water and seawater. The apparatus used in this technique is illustrated in Fig. 5.16. 

Nakashima et al. [719] detail a procedure for preliminary concentration of 16 elements from coastal waters and deep seawater, based on their reductive precipitation by sodium tetrahydroborate, prior to determination by graphite-furnace AAS. Results obtained on two reference materials are tabulated. This was a simple, rapid, and accurate technique for determination of a wide range of trace elements, including hydride-forming elements such as arsenic, selenium, tin, bismuth, antimony, and tellurium. The advantages of this procedure over other methods are indicated. 

It has been reported that the differential determination of arsenic [36-41] and also antimony [42,43] is possible by hydride generation-atomic absorption spectrophotometry. The HGA-AS is a simple and sensitive method for the determination of elements which form gaseous hydrides [35,44-47] and mg/1 levels of these elements can be determined with high precision by this method. This technique has also been applied to analyses of various samples, utilising automated methods [48-50] and combining various kinds of detection methods, such as gas chromatography [51], atomic fluorescence spectrometry [52,53], and inductively coupled plasma emission spectrometry [47]. 

Cutter et al. [121] have described a method for the simultaneous determination of arsenic and antimony species in sediments. This method uses selective hydride generation with gas chromatography using a photoionization detector. 

The optimal reaction conditions for the generation of the hydrides can be quite different for the various elements. The type of acid and its concentration in the sample solution often have a marked effect on sensitivity. Additional complications arise because many of the hydrideforming elements exist in two oxidation states which are not equally amenable to borohydride reduction. For example, potassium iodide is often used to pre-reduce AsV and SbV to the 3+ oxidation state for maximum sensitivity, but this can also cause reduction of Se IV to elemental selenium from which no hydride is formed. For this and other reasons Thompson et al. [132] found it necessary to develop a separate procedure for the determination of selenium in soils and sediments although arsenic, antimony and bismuth could be determined simultaneously [133]. A method for simultaneous determination of As III, Sb III and Se IV has been reported in which the problem of reduction of Se IV to Se O by potassium iodide was circumvented by adding the potassium iodide after the addition of sodium borohydride [134], Goulden et al. [123] have reported the simultaneous determination of arsenic, antimony, selenium, tin and bismuth, but it appears that in this case the generation of arsine and stibene occurs from the 5+ oxidation state. 

The selective hydride generation-gas chromatographic method [121] using photoionization detection discussed in section 12.10.2.1 for the determination of arsenic III and arsenic V has been applied to the determination of down to 3.3pmol L 1 of antimony (Sb III, SbV) in sediments. 

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. 

Pahlavanpour et al. [115] has described a method based on hydride generation and ICP-emission spectrometry for the determination of arsenic, antimony and bismuth in herbage. 

Methods for several metals or metalloids involve conversion to a volatile form. Arsenic, antimony, and selenium can be reduced to their volatile hydrides, AsH3, SbH3, and H2Se, repectively, which can be determined by atomic absorption or other means. Mercury is reduced to volatile mercury metal, which is evolved from solution and measured by cold vapor atomic absorption. 

These workers showed that dissolved arsenic and antimony in natural waters can exist in die trivalent and pentavalent oxidation states, and the biochemical and geochemical reactivities of these elements are dependent upon their chemical forms. They developed a method for the simultaneous determination of arsenic (III)+antimony (III+V)+ antimony (III+V) that uses selective hydride generation, liquid nitrogen cooled trapping, and gas chromatography-photoionisation detection. The detection limit for arsenic is lOpmol L 1 while that for antimony is 3.3pmol L 1 precision (as relative standard deviation) for both elements is better than 3%. 

For organometalloid/organometallic compounds of arsenic, antimony and bismuth, all of the available directly determined enthalpies of formation are shown in Table 1, together with an indication of the experimental method used to obtain them and the appropriate literature references. Also included in Table 1 are the available enthalpy of formation data for the homoleptic hydrides, alkoxides and thiolates, respectively, because ... 

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. 

FP-4 (zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony)—are only slightly soluble (<1 wt %) in the process alloy, thus will partition between both product streams. The process, as presented, offers no method of FP-4 removal and possibly an unwanted increase in these products would occur if the fuel were to be recycled. However, it would be possible to separate the FP-4 from the plutonium/thorium stream by recovering the plutonium/thorium by hydriding. The FP-4 do not form stable hydrides and would remain in solution. 

Gas-phase spectrophotometric method was proposed for the determination of arsenic in tap water after the conversion into hydride, its collection in a trap cooled by liquid N2 and subsequent evaporation at 80°C in a flow of N2. The recovery of 73-86.7% As was reported. Simultaneous determination of arsenic, antimony, selenium and tin was accomplished. 

Antimony, arsenic, selenium, tellurium, bismuth and tin are able to form volatile hydrides by reaction with NaBH4. This property of these metals is used for the hydride atomizing technique. In this method, the metal hydrides are atomized in quartz cuvette by electrical heating. 

The principal methods used for detection and quantification of antimony in biological and environmental samples are various modifications of neutron activation analysis (NAA) and atomic absorption spectrometry (AAS) (ATSDR 1992). AAS techniques (including matrix modification, hydride-formation and flameless AAS) - eventually after enrichment - have proved especially... 

Hydride generation techniques provide a method for introducing samples containing arsenic, antimony, tin. selenium, bismuth, and lead into an atomizer as a gas. Such a procedure enhances the detection limits for these elements bv a factor of lOio l(K). Because several of those species are highl> toxic, delerrnining them at... 

Dialkylamino derivatives of elements located in the periodic table to the left or below those listed above cannot be prepared by the above method due to either the ionic character of some of the inorganic halides or the formation of stable metal halide-amine addition products. Therefore, other methods must be applied. Dialkylamino derivatives of tin and antimony are conveniently obtained by reaction of the corresponding halides with lithium dialkylamides. Others, such as the dialkylamino derivatives of aluminum, are made by the interaction of the hydride with dialkylamines. Dialkylamino derivatives of beryl-lium or lithium result from the reaction of the respective alkyl derivative with a dialkylamine. 

The higher reactivity of this reagent allows its use for the formation of volatile hydrides of antimony, arsenic, bismuth, germanium, lead, selenium, tellurium, and tin. This method is not only superior to the Zn/HCl method due to the wider range of elements that are accessible, but also with respect to speed, efficiency of the reaction, and reduced contamination. The reaction is essentially completed within 10—30 s, and the reagent is typically added into the acidified samples as 0.1—10% (w/v) solution. These factors contribute to the ease of automation which has been a key factor in the success of the hydride generation technique. 

To obtain high molecular weights by this method, almost complete removal of the phenol is required. The reaction is carried out with typical basic catalysts, like lithium hydride, zinc oxide, or antimony oxide under an inert atmosphere. The initial reaction temperature is 150 C. It is raised over a one-hour period to 210 °C while the pressure is reduced to 20 mm Hg. The reaction mixture is then heated to about 300 °C for 5-6 hours at 1 mm Hg. Heating is stopped when the desired viscosity is reached. 

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