Anions in seawater - Determination of Anions in Natural and Treated Waters - page 356

report of Lewin and Avrahami [19] that substantial bromate was formed in their 0.05M
hypobromide solutions. The solutions used by Macalady et al. [17] which correspond to
current chlorine use, were 1000 times more dilute. Using their rate constants, they
calculated in their solutions a conversion to bromate of less than 1% after 24h.
The loss of residual oxidants does not correspond exclusively to bromate formation,
and other reactions, including oxidation of organic matter and perhaps those in equation
(1) above, also take place. The rate and extent of bromate formation depend on the
intensity of sunlight.
Solutions of 10 − 5 M sodium bromate in sea water were also titrated by using the
residual oxidants procedure. The results show that only about 5% of the added bromate
appears as residual oxidants. Thus, the apparent residual oxidants remaining after
exposure to sunlight could be completely due to bromate.
3.10 Bromide
3.10.1 Titration method
Bromide in seawater can be determined by the procedure described below which is
capable of determining down to 0.1mgL −1 bromide.
The sample is acidified with sulphuric acid. The bromide content is then determined by
the volumetric procedure described by Kolthoff and Yutzy [20]. In this procedure the
buffered sample is treated with excess sodium hypochlorite to oxidise bromide to
bromate. Excess hypochlorite is then destroyed by addition of sodium formate.
Acidification of the test solution with sulphuric acid followed by addition of excess
potassium iodide liberates an amount of iodine equivalent to the bromate (ie the original
bromide) content of the sample. The liberated iodine is titrated with standard sodium
thiosulphate.
3.10.2 Segmented flow analysis
Basel et al. [21] have described methods for compensation for chloride, ammonia and
bicarbonate interferences in determining bromide in saline waters with an automated
segmented flow analyser utilising the phenol red method.
3.10.3
Isotachoelectrophoresis
Fukushi and Hiro [22] have described a capillary-type isotacho-electrophoretic method
for the determination of bromide in seawater.
3.10.4 Solid state membrane electrodes
Walters [23] has examined the effect of chloride on the use of bromide and iodide solid
state membrane electrodes and he calculated selectivity constants. Multiple linear