Anions in seawater - Determination of Anions in Natural and Treated Waters - page 357

regression analysis was used to determine the concentrations of bromide, fluoride and
iodide in geothermal brines and indicated high interferences at high salt concentrations.
The standard curve method was preferred to the multiple standard addition method
because of:
(1) The deviation from linearity at high salt concentrations of the bromide electrode.
(2) The loss of accuracy due to increase in sample volume by using volume increments.
(3) The limitations in reading from the Orion meter (0.1mV).
(4) The fact that bromide, fluoride and iodide were present at relatively low
concentrations (where the electrode exhibited non-linear behaviour).
3.10.5 X-ray fluorescence spectroscopy
Sichère et al. [24] determined bromine concentrations in the 0.06-120mg L −1 range in
brines directly by X-ray fluorescence using selenium as an internal standard to eliminate
interference effects. Lower concentrations of bromine must be concentrated on filter
paper containing an ion exchange resin. The same concentrations of chlorine can be
determined with the addition of barium to reduce the interferences from carbonates and
sulphates. Relative standard deviation was better than 1%.
In this method barium is added to reduce interference by carbonates and sulphates. The
interference of some other ions, eg calcium, potassium, magnesium, sodium, strontium
and iron was examined.
3.10.6 X-ray emission spectrometry
Rose and Cuttita [25] proposed a graphical method for evaluating the background when
determining traces of bromide by X-ray emission spectrography (carried out on cellulose
pellets containing the residue from evaporation of the sample in the presence of standard
bromide solution). Based on this work a graphical method is proposed which provides a
value (m B ) of the amount of bromide equivalent to the background, which is substituted
into the equation: counts per sec=k ( m +m s +m B ), where k is a factor depending on the
sample, m is the bromide content of the original solution and m s is the amount of
bromide added as 'spike'. Results obtained by both methods agree satisfactorily but it is
stressed that both methods are approximations.
3.10.7 Electrostatic ion chromatography
The application of this technique is discussed under multianion analysis in section 3.32.2.
3.10.8 Miscellaneous
Foti [26] has studied the feasibility of concentrating traces of radioactive bromide ions by
passing the seawater sample through a column of inactive silver bromide (to effect
isotopic exchanges). The effects of column height and of flow rate, volume and/or
residence time of the seawater on the extent of exchange were examined; each of these
variables had significant effect.