Antimony hydrides detection

Figure 6.4 shows the change in the sensor conductivity as a function of temperature. Curve / shows the dependence of sensor resistivity with temperature when the sensor is positioned in evacuated installation. The introduction of antimony hydride was made at temperature - 75°C bringing about no change in resistivity. When the temperature of the sensor was increased up to - 20 C there were no effects detected on its resistivity caused by antimony hydride. Only at higher temperatures one can observe deviation of dependence RiT) from curve 1 which is caused by decomposition of SbHa on ZnO. These results led to experiments on emission of H-atoms in a special vial when Sb-film treated by H-atoms was kept at a room temperature and sensors were kept at the temperature of - 80 C. Under these conditions, as is shown by above reasoning. 

The first reports on organometallic antimony compounds in the aquatic environment were in the early 1980s, using HG-GC-AAS. More recently, the nature of the standard compounds used for the analysis has been questioned, " and the experimental conditions used for the hydride generation during analysis are now known to produce artefacts.The molecular structure of the compounds with carbon-antimony linkages detected in the environment in the early reports therefore remains unresolved. 

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. 

De Oliviera et al. [739] have described a technique for determining these elements based on the hydride generation technique. Detection limits are 1 xg/l for arsenic and antimony, and 0.5 pg/1 for selenium. 

Braman et al. [34] used sodium borohydride to reduce arsenic and antimony in their trivalent and pentavalent states to the corresponding hydrides. Total arsenic and antimony are then measured by their spectral emissions, respectively, at 228.8 nm and 242.5 nm. Limits of detection are 0.5 ng for antimony and 1 ng for arsenic, copper, and silver. Oxidants interfere in this procedure. 

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]. 

Tin, antimony, and selenium hydrides, produced by the borohydride reduction technique, were found to chemiluminesce with ozone in an analytical detection scheme. Limits of detection were 35, 10, and 110 ng of Sn, Sb, and Se,... 

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. 

Figure S.2 shows a schematic diagram of the automatic hydride/vapour-generator system designed by P.S. Analytical. This has been widely used to determine hydrideforming elements, notably arsenic, selenium, bismuth, tellurium and antimony, in a wide range of sample types. To provide a wide range of analyses on a number of matrices the chemistry must be very well defined and consistent. Goulden and Brooksbank s automated continuous-flow system for the determination of selenium in waste water was improved by Dennis and Porter to lower the detection levels and increase relative precision [10, 11]. The system described by Stockwell [9] has been specifically developed in a commercial environment using the experience outlined by Dennis and Porter.

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. 

Selective extractive separation of antimony (usually Sbm), as well as selective complexation of Sbm (Mohammad et al., 1990), followed by hydride generation have been used for the determination of antimony in water. Four species of antimony in natural water have been identified Sbv, Sbm, methylantimony and dimethylantimony (Apte et al., 1986). The analyses were carried out using hydride generation cold trapping procedures. Sbm was separated from Sbv in natural and waste waters by extraction with N-p-methoxyphenyl-2-furylacrylohydroxamic acid into chloroform (Abbasi, 1989). The extracted antimony was determined by means of graphite-furnace AAS. The detection limit was 10 2mgdm 3. 

Cutter, L.S., Cutter, G.A. and Diego-McGlone, M.L.C. (1991) Simultaneous determination of inorganic arsenic and antimony species in natural waters using selective hydride generation with gas chromatographic/photoionization detection. Anal. Chem., 63, 1138-1142. 

Kusaka et al. [760] generated the gaseous hydrides of antimony(III), arsenic(III) and tin by sodium borohydride reduction. The hydrides were swept from solution onto a Porapak Q column where they were separated and detected at a gold gas-porous electrode by measurement of the respective electro-oxidation currents. Detection limits for 5ml samples were As(III) (0.2pg L ) Sn(II) (0.8pg L 1) Sb(III) (0.2pg L 1). The order of elution is hydrogen, arsine, stannane, stibine and mercury, ie the order of increasing molecular weight. 

Vien and Fry [762] have reported a gas chromatographic determination of arsenic, selenium, tin and antimony in natural waters. The gaseous hydrides are generated, concentrated on a cold trap, and then injected into the gas chromatograph with the use of drying agents or carbon dioxide scrubbing. A specially conditioned Tenax column suppresses unwanted byproduct elution and separates the volatile hydrides at room temperature. A photoionisation detector was used and the authors reported a detection limit as low as 0.001 pg L ... 

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%. 

Atmospheric particulates, collected on Whatman 41 cellulose filters, are decomposed with sulfuric acid and hydrogen peroxide for subsequent determination of antimony and bismuth and with sulfuric acid and nitric acid for tin. Each element is analyzed independently by hydride generation/atomic absorption spectrometry. The optimization of instrumental as well as chemical parameters is described. The precision of the entire procedure is generally better than 10%. The detection limits are 0.25 ng m" for antimony and tin and 0.13 ng m for bismuth if 400 m of air are filtered and a 2 ml aliquot of the initial 50 ml sample solution is analyzed. 

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. 

Vien S. H. and Fry R. C. (1988) Ultrasensitive simultaneous determination of arsenic, selenium, tin and antimony in aqueous solution by hydride generation gas chromatography with photoionisation detection, Anal Chem 60 465-472. 

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... 

Since the hydride technique only permits detection of antimony which is present ionogenically in solution, decomposition is required for organic or complexed antimony. Organically loaded water samples must also be decomposed before measurement. 

For trace analysis, the main ceramic elements of interest are Zn, Pb, Cu, Bi, Sb, Sn, Ag, As, Mn, Cr, Se, and Hg. Many of these are environmentally important. In certain cases the detection limits of flame AAS are inadequate, so that hydride generation for antimony, selenium, arsenic and bismuth, cold vapor for mercury, and graphite furnace AAS for lead and cadmium are required. A variation of AAS is atomic fluorescence, and this is used to achieve the detection limits needed for Hg and Se in environmental samples. Microwave digestion techniques for sample preparation are becoming more common, where, unlike fusion, there is no risk of loss of volatile elements from unfired samples and fewer reagents are... 

---