Antimony selective determination

With the exception of antimony (V), which requires the presence of iodide for its reduction, all species can be reduced in an acid medium at a pH of 1 -2. However, the reduction of some species, including antimony (III), arsenic (III), and all tin species, will also proceed at higher pH, where arsenic (V) and antimony (V) are not converted to their hydrides. This effect permits the selective determination of the various oxidation states of these elements [714, 716]. In the case of tin, reduction can be achieved at the pH of the Tris-HCl... 

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 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 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 compound is cautiously dissolved in nitric acid and the solution is appropriately diluted for the analysis of antimony by AA spectrophotometry or ICP emission spectrophotometry and fluoride ion is determined by ion—selective electrode or ion chromatography. 

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. 

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%. 

Wire that senses pH changes such as antimony metal can be coated with urease (65) and used to determine urea in pure blood (66). Covering the antimony metal with a gas perm-selective membrane (67) improves the selectivity. The microsensors respond from 0.1 to 10 mM urea in 30-45 s. This ammonia sensor has a faster baseline recovery than commercial gas membrane electrodes. 

In view of these observations it would seem sensible that the influence of adjacent superficial antimony and tin ions should also be considered in terms of likely mechanisms. Immediately one would recall the suggestion (72) that the catalytic properties may be related to the blue color of the material, which has been associated with a possible Sb -Sb charge transfer process. Such an association may then be related to the kinetics of butene oxidation, which have been interpreted in terms of the formation of allylic intermediates at active centres containing Sn and Sb ions. Indeed, McAteer (76) has suggested that these active centers have acidic and basic functions and consist of surface oxide ions of different electron density as determined by the coordinated cations. McAteer described the pattern of selectivity for the formation of butadiene and a-ketone according to the depiction in Fig. 7a. The initial step was postulated as the formation at an acid center of a positively charged allyl ion which is ti or a bonded at an adjacent basic site. The formation of butadiene was attributed to proton abstraction from the zr-allyl intermediate, its facile desorption at surfaces... 

In the methods of Sb determination use is made of ion-associates SbCU with Rhodamine B and other basic dyes. The methods are highly sensitive and selective. A simple iodide method is commonly used to determine higher antimony concentrations. 

Example Applications. Previous work has mostly been concerned with testing the theoretical models and obtaining proof of concept (29,39). Antimony pH tips were used to image the activity of urease immobilized in a disk of glutaraldehyde/BSA gel and to quantify the total flux of H+ in the presence of a saturating concentration of urea (29). Wei et al. (39) showed that urease kinetics can also be quantified using an ammonium-selective neutral carrier-based tip to determine the concentration profile of NHj produced by the hydrolytic reaction... 

Selective substoichiometry has been proposed and applied to the determination of antimony in different oxidation states methylmercury and butyl tin species... 

Alloys of Cu, Sb, Pb, and Sn. This procedure for analysis of bearing metals relies on two successive depositions of pairs of metals. Each (mixed) deposit is dissolved, and then one of the components is selectively deposited (and determined) under different conditions and the other component determined by the difference. First, copper and antimony are codeposited from HCl, with hydrazine as a depolarizer. The (weighed) deposit is dissolved in nitric/ hydrofluoric acid, which retains antimony in solution as a fluoride complex, allowing deposition of pure copper (at —0.40 V). Tin and lead are codeposited (at —0.70 V) from the initial residual solution. After redissolution of the (weighed) deposit in nitric/hydrofluoric acids, lead is deposited ano-dically as PbOi- The Pb and Sn aspect of this procedure is useful for analysis of solders. An analogous procedure allows Ni and Co separation (via C02O3). 

Microcomponents Inorganic microcomponents cover almost the entire periodic table. Here we discuss only those elements that are determined most frequently beryllium, vanadium, chromium, cobalt, nickel, copper, zinc, arsenic, selenium, silver, cadmium, antimony, barium, and lead. The techniques of choice are FAAS, graphite furnace-AAS (GF-AAS), ICP, and hydride generation-AAS (HG-AAS). An ultrasonic nebulizer has recently become commercially available for FAAS and ICP-AES, which decreases the lower determination limits. ICP-mass spectrometry (ICP-MS) is a recent development in which ionization is combined with sensitive mass discrimination. In a further development a graphite furnace is used in front of the ICP-MS. Selective evaporation of elements in the graphite furnace reduces the influence of highly interfering matrices. ICP-MS is expensive, which deters its widespread use. 

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