Bromate stability

Previous sections of this chapter discussed the details of newly developed analytical methodologies and strategies for bromate separation and trace quantification. This confirms the current vast interest of the analytical community in bromate determination as a result of ongoing regulatory requirements. The acceptance of such methods depends mainly on the analytical performance as related to accuracy and precision. However, despite all analytical efforts, very little work has been done to investigate the stability of bromate species between sampling and analysis in different water matrices. Studies of bromate stability in water matrices should be carried out before any analytical methodology can be approved. 

Bromate stability was studied in two different dimensions. The first was related to direct evaluation of bromate stability in different water matrices. The second was devoted to stability of bromate species mobilized on activated alumina micro-columns with a view to developing a field sampling methodology from bromate in waters. 

The high total hardness stability tests were extended to more than 100 days and bromate results using the FI-ICP-MS method eonfirmed the stability of bromate over this period. Similarly the presence of 50 mg/L EDA preservative showed no effect on bromate stability. High total hardness water samples were further re-analysed after a period of 100 days and bromate content was found to be stable. 

Table 2.5 Soft and hard water samples investigated for bromate stability...

The previous section addressed the effect of water matrix on bromate stability. This section investigates the possibility of developing an alternative approach to sampling of bromate species in waters by employing columns of a selective packing material. This study was based on the development of an FI system with aluminamicrocolumns... 

The stability of the halate(I) ion decreases, as expected, from C10 to 10 and only the chlorate(I) ion can be considered reasonably stable even in aqueous solution. Solid sodium bromate(I). NaBrO (with five or seven molecules of water of crystallisation) can be obtained, but on standing or warming it disproportionates ... 

The modes of thermal decomposition of the halates and their complex oxidation-reduction chemistry reflect the interplay of both thermodynamic and kinetic factors. On the one hand, thermodynamically feasible reactions may be sluggish, whilst, on the other, traces of catalyst may radically alter the course of the reaction. In general, for a given cation, thermal stability decreases in the sequence iodate > chlorate > bromate, but the mode and ease of decomposition can be substantially modified. For example, alkali metal chlorates decompose by disproportionation when fused ... 

Apparent indicator constant 264, 267 Apparent stability constant 59 Aqua regia 111 Arc alternating current, 764 direct current, 763, 771 sensitivities of elements, (T), 766 Aromatic hydrocarbons analysis of binary mixtures, 715 Arsenates, D. of (ti) 357 Arsenic, D. of as silver arsenate, (ti) 357 as trisulphide, (g) 448 by iodine, (am) 634, (ti) 397 by molybdenum blue method, (s) 681 by potassium bromate, (ti) 406 by potassium iodate, (ti) 401 in presence of antimony, (s) 724 Arsenic(III) oxide as primary standard, 261... 

Bancroft and Gesser [870] conclude that kinetic factors are predominant in determining whether decomposition of a metal bromate yields residual bromide or oxide. The thermal stabilities of the lanthanide bromates [877] and iodates [877,878] decrease with increase in cationic charge density, presumably as a consequence of increased anionic polarization. Other reports in the literature concern the reactions of bromates of Ag, Ni and Zn [870] and iodates of Cd, Co, Mn, Hg, Zn [871], Co and Ni [872], Ag [864], Cu [867], Fe [879], Pb [880] andTl [874]. 

Unstabilized hypobromite solutions are even more unstable than hypochlorite. Hypobromite disproportionates to bromate (Br03), a toxic and potentially carcinogenic compound, in alkaline conditions. The stabilizer in STABREX inhibits that process as shown in Table3. 

From these measurements it appears that the stability of the compounds does not follow the expected order of chlorate < bromate < iodate. This behavior, however, cannot be regarded to be a characteristic property of ammonium halogenates only, because according to our experiments the same order of stability has been found in case of potassium halates. It is fairly difficult to propose a reliable reaction mechanism merely from kinetic data... 

Comparing the stability of the triammincs of silver halides, the chloride is more stable than the bromide, and the iodide cither does not exist or is very unstable. This is contrary to the usual observations in the ammines, where the stability of the ammine rises from chloride to iodide. In the case of the ammines of the oxy-halogen salts of silver the most unstable is the iodate, which is non-existent at ordinary pressure, then comes the bromate, and the most stable is the chlorate.3... 

The weak complexing of indium(III) with chlorate, bromate and iodate has been studied, and stability constants reported, but no preparative work has been done. Perchlorate ion does not complex with indium(III).9... 

Cystine, which contains a disulfide bond, is reported to be the most numerous and reactive amino acid present in hair keratin. Disulfide bonds in cystine are reduced by mercaptans and phosphines, and oxidized by perborates, bromates, and bleach. These reactions result in structural rearrangements within keratin which may affect the physiochemical properties of hair, since disulfide bonds in cystine contribute to the stability of hair. For example, hydrogen peroxide bleaching of hair is an oxidative process which occurs readily in an alkaline medium. This results in the formation of perhydroxy anions which have been proposed to react with cystine to form cysteic acid residues. The process of bleaching results in the loss of approximately 15% of the cystine bonds originally present in keratin and may explain the increased permeability of bleached hair to chemicals. - ... 

Electrode-Preparation and Aging. Electrode preparation procedures are given by Keston (14) and by Ives and Janz (II). Electrodes were prepared from a paste containing 90% silver oxide and 10% silver bromate placed on a platinum spiral and heated in a furnace for 7 min at 650°C. Janz and Taniguchi (12) have reviewed the preparation, reproducibility, and stability of this electrode. Taylor and Smith (13) found the equilibrium potential to be stable within 0.02 mV. Electrodes... 

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