Anions in surface, ground, mineral, borehole and pure waters - Determination of Anions in Natural and Treated Waters - page 456

6.2.3 Bromide
6.2.3.1 Segmented flow analysis
Basel et al. [13] have discussed methods for compensating for chloride, ammonia and
bicarbonate in the automated phenol red segmented flow analysis method for the
determination of bromide in groundwaters.
6.2.3.2 Polarography
In a specific method for determining down to 2mg L −1 bromide in groundwaters [14]
bromide is first converted to silver bromide which is then oxidised to silver bromate
which is then determined polarographically.
Polarographic methods for bromide are based on the oxidation of bromide to bromate
followed by electro-reduction. In this technique, iodide is partially oxidised to iodate.
The oxidation reaction is
and the global electrode reaction
The half-wave potential for the reduction of iodate is less negative than is that of
bromate.
Reagents. Merck unless otherwise stated.
Potassium chloride. Potassium bromate. Sodium acetate N.
Silver nitrate, 0.1N.
Sodium hydrochlorite (BDH), low in bromine.
Activated carbon (pa Baker).
The method is directly applicable to samples containing 1-150µg bromide. Adequate
volumes are sampled and processed to fall within this range of applicability.
For surface waters or ground waters containing organic compounds shake the sample
for 30min after adding 1g L −1 activated carbon powder, and subsequently filter on a
standard bacteriological membrane filter with a porosity of 0.45µm. Organobromated
compounds are eliminated.
To concentrate the sample, precipitate bromides simultaneously with chlorides and
iodides by adding 25ml of 0.1N silver nitrate solution to 1L sample water and leaving in
the dark for 12h. Bromate, if present, remains unprecipitated as silver bromate which is
soluble.
The precipitate is filtered under vacuum on a membrane with pore size of 0.45µm and
the membrane with the deposit is placed in a 100ml vessel for about 30min in a drying