Bromide, in seawater

The average concentration of bromine (as bromide) in seawater is 65 ppm. Calculate... 

Bromide in seawater can be determined by the procedure described below, which is capable of determining content down to 0.1 mg/1 bromide. 

Fukushi and Hiro [26] have described a capillary-type isotachoelectrophoretic method for the determination of bromide in seawater. 

There is enough bromide in seawater at 35%o salinity to convert 60 mg/1 of chlorine to hypobromite. 

Sheeter [17] has discussed an ultraviolet method for the measurement of ozone in seawater. Crecelius [18] has discussed oxidation products obtained (bromine, hypobromous acid, bromate) when bromides in seawater are oxidised by ozone. 

Bromine occurs in the form of bromide in seawater and in natural brine deposits (see Chemicals from brine). Chloride is also present. In all current methods of bromine production, chlorine, which has a higher reduction potential than bromine, is used to oxidize bromide to bromine. 

Bromine occurs as bromide in seawater (0.188% Br), in the mother liquor from salt wells of Michigan. Ohio. West Virginia. Arkansas, and in the potassium deposits of Germany and France. 

The iodometric method, principally developed by Kolthoff and Yutzy (1937) and first applied to seawater analysis by Thompson and Korpi (1942) is the most accurate procedure for the estimation of bromide in seawater. 

Occurrence. Magnesium bromide [7789-48-2] MgBr2, is found in seawater, some mineral springs, natural brines, inland seas and lakes such as the Dead Sea and the Great Salt Lake, and salt deposits such as the Stassfurt deposits. In seawater, it is the primary source of bromine (qv). By the action of chlorine gas upon seawater or seawater bitterns, bromine is formed (see Chemicals frombrine). 

The basis of this method is that when normal seawater is chlorinated at the usual levels of 1 to 10mg/l of chloride, the bromine in seawater (8.1 x 10 4 M, 65 mg/1 at salinity = 35%o) is rapidly and quantitatively oxidised to Br() and HBrO. If 50 mg/1 of bromide is added to distilled or fresh waters containing HCIO plus C1CT, then HBrO plus BrO" are both formed. The HBrO plus BrO" will in turn rapidly brominate fluorecein (9-[o-carboxyphenyl]-6-hydroxy-3-isoxanthenone) to give the pink tetrabromo derivative eosin yellow (2,4,5,7-tetrabromo-9-[o-carboxyphenyl]-6-hydroxy-3-isoxanthenone), provided the molar ratio of bromide to fluorescein is 4 1. The resultant increase in eosin can be measured visually or spectrophotometrically, and the decrease in fluo-roscein measured fluorometrically. If the molar ratio of bromide to fluoroscein is < 4 1, then the mono-, di-, and tri-bromo derivatives are formed repro-ducibly. These derivatives have extinction coefficients close to eosin and are accounted for in the standardisation. 

Brown and Bellinger [123] have proposed an ultraviolet technique that is applicable to both polluted and unpolluted fresh and some estuarine waters. Humic acid and other organics are removed on an ion exchange resin. Bromide interference in seawater samples can be minimised by suitable dilution of the sample but this raises the lower limit of detection such that only on relatively rich (0.5 mg/1 NO3N) estuarine and inshore waters could the method be used. Chloride at concentrations in excess of 10 000 mg/1 do not interfere. 

Removal of inorganic interferences, particularly the removal of bromide interference in seawater by fivefold dilution of the sample, the removal of nitrate by addition of sulfamic acid, and the removal of metals by passage through Amberlite IR 120 cation exchange resin. 

Other methods for the determination of chlorine in seawater or saline waters are based on the use of barbituric acid [13] and on the use of residual chlorine electrodes [ 14] or amperometric membrane probes [15,16]. In the barbituric acid method [12], chlorine reacts rapidly in the presence of bromide and has completely disappeared after 1 minute. This result, which was verified in the range pH 7.5-9.4, proves the absence of free chlorine in seawater. A study of the colorimetric deterioration of free halogens by the diethylparaphenylene-diamine technique shows that the titration curve of the compound obtained is more like the bromine curve than that of chlorine. The author suggests... 

Howard [27] determined dissolved aluminium in seawater by the micelle-enhanced fluorescence of its lumogallion complex. Several surfactants (to enhance fluorescence and minimise interferences), used for the determination of aluminium at very low concentrations (below 0.5 pg/1) in seawaters, were compared. The surfactants tested in preliminary studies were anionic (sodium lauryl sulfate), non-ionic (Triton X-100, Nonidet P42, NOPCO, and Tergital XD), and cationic (cetyltrimethylammonium bromide). Based on the degree of fluorescence enhancement and ease of use, Triton X-100 was selected for further study. Sample solutions (25 ml) in polyethylene bottles were mixed with acetate buffer (pH 4.7, 2 ml) lumogallion solution (0.02%, 0.3 ml) and 1,10-phenanthroline (1.0 ml to mask interferences from iron). Samples were heated to 80 °C for 1.5 h, cooled, and shaken with neat surfactant (0.15 ml) before fluorescence measurements were made. This procedure had a detection limit at the 0.02 pg/1 level. The method was independent of salinity and could therefore be used for both freshwater and seawater samples. 

The chemiluminescence technique has been used to determine trivalent chromium in seawater. Chang et al. [187] showed Luminol techniques for determination of chromium (III) were hampered by a salt interference, mainly due to magnesium ions. Elimination of this interference is achieved by seawater dilution and utilising bromide ion chemiluminescence signal enhancement (Fig. 5.7). The chemiluminescence results were comparable with those obtained by a graphite furnace flameless atomic absorption analysis for the total chromium present in samples. The detection limit is 3.3 x 10 9 mol/1 (0.2 ppb) for seawater with a salinity of 35%, with 0.5 M bromide enhancement. 

The effect of calcium interference is somewhat different. At its concentration in seawater, 0.010 M, calcium ion had no effect upon chemiluminescence analysis of a 6 x 10 8 M Crm solution in the absence of bromide ion. The... 

Another approach consists of an in-situ acetylation and extraction of NPEOs and further analysis of the acetyl derivatives. The method has been applied to analyse effluent water and sewage sludges [102,103], sediments [104] and river waters [105]. Silylated derivatives [106] using BSA or BSTFA have also been used to determine NPEO (n < 6) in seawater [107] and wastewater [107,108], sediments [109] and sludges from wool scour effluents [110]. Halogenated derivatives of alkylphenols (AP) can also be formed as a result of chlorination practices in water treatment or wastewater if bromide is present. Brominated OPs and NPs (BrAPEOs) have been identified by GC-MS in sewage [111] and tap water [89], respectively. 

Bromine occurs in nature as bromide in many natural brine wells and salt deposits. It also is found in seawater at a concentration of 85 mg/L. The element was discovered by A. J. Balard and C. Lowig, independently in 1826. Bromine is used in bleaching fibers and as a disinfectant for water purification. Other appbcations are in organic synthesis as an oxidizing or brominat-ing agent in the manufacture of ethylene dibromide, methyl bromide and other bromo compounds for dyes and pharmaceutical uses as a fire retardant for plastics and in chemical analysis. Ethylene dibromide is used in anti-... 

Brominated compounds widely occur in marine organisms, particularly seaweeds and invertebrates. Many of them play a defensive role against parasites and predators, and are incorporated by opisthobranch mollusks to this scope from the diet. Bromine is uptaken by seaweeds and invertebrates from bromide dissolved at sparingly 1 mM concentration in seawater. The process is catalyzed by haloperoxidases, which have been characterized both as structure and function (Butler 1997). 

A third factor comes into play in bromine chemistry, which is that atmospheric solutions containing bromide and chloride are most typically formed from seawater. Wave action generates small airborne droplets of seawater, which thus initially contain the elements in the ratios found in seawater. The molar ratio of Br- to Cl- is 1 650. However, despite the relatively small amounts of bromide relative to chloride, it plays a disproportionate role because of its reactivity and because its chemistry is closely intertwined with chloride ion chemistry. Table 8.16, for example, shows some of the interhalogen reactions of bromide and chloride. It can be seen that the chemistry preferentially generates Br2 rather than Cl2. 

Bromine is a dense, red, volatile, corrosive liquid (bp 59 °C) that is best made by oxidizing the small amount of Br in seawater with chlorine (higher bromide concentrations occur in the Dead Sea and in certain natural brines, e.g., in Arkansas and Michigan). The vapor of the resulting Br2 is then carried off in an air stream ... 

The half-life with respect to chemical transformation of CH3I in seawater at 20°C was determined to be 20 days, as compared to about 200 days in freshwater (reaction with H20 yielding CH3OH). In a case of a groundwater contamination with several alkyl bromides, Schwarzenbach et al. (1985) reported the formation of dialkyl sulfides under sulfate-reducing conditions in an aquifer. They postulated that in an initial reaction, primary alkyl bromides reacted with HS" by an SN2 mechanism to yield the corresponding mercaptans (thiols) ... 

Table 5), and several are now being used, or are potentially useful, for measuring key ocean elements. The most common use of direct potentiometry (as compared with potentiometric titrations) is for measurement of pH (Culberson, 1981). Most other cation electrodes are subject to some degree of interference from other major ions. Electrodes for sodium, potassium, calcium, and magnesium have been used successfully. Copper, cadmium, and lead electrodes in seawater have been tested, with variable success. Anion-selective electrodes for chloride, bromide, fluoride, sulfate, sulfide, and silver ions have also been tested but have not yet found wide application. 

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