Bromate determination methods

With reference to bromate determination, there have been few published flow injection (FI) studies. Gordon et al. (1994) described a spectrophotometric procedure based on the oxidation of chlorpromazine (CLP). A low limit of quantitation (0.8 ug/L) was realized but the method was susceptible to interference by cations and other co-oxidants. 

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. 

The results obtained for the vast majority of the laboratories carrying out the ISO 15061 IC method were considered to be fit for the purpose. In addition to this method, five alternative methods suitable for trace bromate determinations were also considered, namely on-line IC-ICP-MS, simple on-line column chromatography ICP-MS, IC with chlorpromazine post-column reaction and colorimetric detection, and fluorescence quenching with Carbostyril (with pre-treatment), which are all capable of achieving a bromate detection limit below 1 xg/L. A field method with methylene blue and fluorescence quenching with Carbostyril without sample pretreatment did not lead to satisfactory results at this level of bromate concentrations. 

The interferences of chlorite create a significant problem during bromate determination. A number of procedures have been investigated for removing chlorite without adversely affecting bromate levels. Of these, the procedure that employs Fe(II) in acidic solution was found to be the most effective. The elimination of these intafaing compounds was the final step toward the development of EPA Method 317.0. ... 

Sensitivity for bromate determination has been improved by more than a factor of 10 through the use of a postcolumn derivatization reaction in which HI is generated in situ from K1 and reacts with bromate to form the triiodide anions (la ). In 2000, the U.S. EPA published Method 317.0, which uses postcolumn derivatization with o-dianisidine this reacts with the eluting bromate to form a chromophore, which is then measured with a UVA is detector. This method offers excellent limits of detection, below 1 p-g/L, for bromate, as well as for chlorite and chlorate. 

Hautman, D.P. Munch, D.J. Frehis, Ch. Wagner Pepich, B.V. Review of the methods of the U.S. environmental protection agency for the bromate determination and validation of Method 317.0 for disinfection byproduct anions and low-level bromate. J. Chromatogr. 2001, 920, 221-226. 

Because ODA has been identified as a potential human carcinogen [61], alternative postcolumn derivatizations were evaluated. The method introduced by Weinberg and Yamada [62] is based on the postcolumn derivatization of bromate with bromide under acidic conditions to yield tribromide, Brg, which can be detected by UV at 267 nm. The reaction scheme was already described by Eqs. (8.41) and (8.42) in Section 8.2.I.2. In addition to bromate, this method can also be used for determining other oxyhalides such as iodate and chlorite. 

US EPA (2001) Determination of Inorganic Oxyhalide Disinfection By-Products in Drinking Water Using Ion Chromatography with the Addition of a Post-Coliunn Reagent for Trace Bromate Analysis. Method 317.0, Revision 2.0. US EPA, Cincinnatti, OH, USA. 

The question may arise that since this is bromate— bromide, why not continue in the usual manner. The answer is that coulometric modification increases the accuracy when small amounts of the compound are being determined. Since this method requires a much smaller sample, it can be used whenever a turbidity or color problem occurs with the conventional bromate—bromide method. 

A similar procedure may also be used for the determination of antimony(V), whilst antimony (III) may be determined like arsenic(III) by direct titration with standard iodine solution (Section 10.113), but in the antimony titration it is necessary to include some tartaric acid in the solution this acts as complexing agent and prevents precipitation of antimony as hydroxide or as basic salt in alkaline solution. On the whole, however, the most satisfactory method for determining antimony is by titration with potassium bromate (Section 10.133). 

Determination of chromium as lead chromate (precipitation from homogeneous solution) Discussion. Use is made of the homogeneous generation of chromate ion produced by the slow oxidation of chromium(III) by bromate at 90-95 °C in the presence of excess of lead nitrate solution and an acetate buffer. The crystals of lead chromate produced are relatively large and easily filtered the volume of the precipitate is about half that produced by the standard method of precipitation. 

The polarographic method is applicable to the determination of inorganic anions such as bromate, iodate, dichromate, vanadate, etc. Hydrogen ions are involved in many of these reduction processes, and the supporting electrolyte must therefore be adequately buffered. 

Discussion. In acid solution arsenic(III) can be oxidised to arsenic(V) and antimony(III) to antimony(V) by the well-established titration with a solution of potassium bromate and potassium bromide (Section 10.133). The end point for such determinations is usually observed indirectly, and very good results have been obtained by the spectrophotometric method of Sweetser and Bricker.23 No change in absorbance at 326 nm is obtained until all the arsenic)III) has been oxidised, the absorbance then decreases to a minimum at the antimony(III) end point at which it rises again as excess titrant is added. 

In situ densitometry has been the most preferred method for quantitative analysis of substances. The important applications of densitometry in inorganic PLC include the determination of boron in water and soil samples [38], N03 and FefCNfg in molasses [56], Se in food and biological samples [28,30], rare earths in lanthanum, glass, and monazite sand [22], Mg in aluminum alloys [57], metallic complexes in ground water and electroplating waste water [58], and the bromate ion in bread [59]. TLC in combination with in situ fluorometry has been used for the isolation and determination of zirconium in bauxite and almnimun alloys [34]. The chromatographic system was silica gel as the stationary phase and butanol + methanol + HCl -H water -n HF (30 15 30 10 7) as the mobile phase. 

Another interesting TLC method for the isolation and determination of bromate ion in flour dough and breads has been developed [59]. It involves extraction of BrOj from foodstuff, purification on alumina column, TLC separation on silica gel layer developed with water -1- -butanol + n-propanol (1 1 3), and quantification by densitometry. Bromate ion down to 0.1 pg in bread (1.0 g) was detected with tohdin-FIQ reagent. 

Separation and detection methods Ion chromatography is routinely used for the isolation of bromate. Diverse detection methods are mentioned in the literature, including isotope dilution analysis (Creed and Brockhoff 1999), conductivity measurement (Jackson et al. 1998), fluorimetric determination (Gahr et al. 1998), ICP-MS (Seubert and Nowak 1998) and spectrophotometry (Achilii and Romele 1999),... 

Impact sensitivities of mixtures of red phosphorus with various oxidants were determined in a direct drop-ball method, which indicated higher sensitivities than those determined with an indirect striker mechanism. Mixtures with silver chlorate were most sensitive, those with bromates, chlorates and chlorites were extremely sensitive, and mixtures with sodium peroxide and potassium superoxide were more sensitive than those with barium, calcium, magnesium, strontium or zinc peroxides. Mixtures with perchlorates or iodates had sensitivities comparable to those of unmixed explosives, such as lead azide, 3,5-dinitrobenzenediazonium-2-oxide etc. 

The total iodine procedure is claimed to be relatively free from interference by foreign ions. The iodate procedure is subject to interference by bromate and sulfite ions. This method is claimed to be capable of determining down to 0.1 ig iodine in the presence of 500 mg chloride ion and 5 mg of bromide ion. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

Potassium bromate is a widely used dough conditioner. However, if it is used in excessive quantities in bread products then appreciable residues (> 1 mg/kg) can remain which is of concern since it is a cancer suspect agent. Its routine analysis is laborious, time-consuming and difficult by HPLC, and Cunningham and Warner (2000) described the development of an instrumental neutron activation method for determination of bromine while HPLC was used to determine bromate in selected samples. 

Creed JT, Brockhoff CA, Martin TD (1997) EPA Method 321.8. Determination of bromate in drinking waters by ion chromatography inductively coupled plasma-mass spectrometry. U.S. EPA, Cincinnati, OH, Available at http //www.epa.gov/microbes/m 321 8.pdf... 

Estimation Gravimetrically as Sulphide as Magnesium Pyroarsenate—Volu-metrically by Iodometric Methods with Potassium Bromate, etc.—The Marsh Test—The Gutzeit Test—Fleitmann s Test—Colorimetric Methods— Microohemioal Methods—Determination of Arsenic in Gases. 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

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