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sulphate ions, were partially trapped (5-20%) and did not interfere in the determination
of iodide. The detection limit for iodide was 0.2µg L
−1
for 6mL of artificial seawater.
This method was applied to determination of iodide (ND—18.3µg L
−1
) and total
inorganic iodine
in seawater samples taken near Japan.
3.18.5
High performance liquid chromatography
Varma
et al.
[108] determined iodide in seawater in amounts down to 2ng L
−
1
by a
method based on precolumn derivativisation of the iodide into 4-iodo-2,6
dimethylphenol. An ultraviolet detector was employed.
3.18.6
Electrostatic ion chromatography
The application of this technique is discussed under multianion analysis in section 3.32.2.
3.18.7
Miscellaneous
Buchberger
et al.
[109] carried out a selective determination of iodide in brine. The
performance of a potentiometric method using an ion selective electrode and of liquid
chromatography coupled with ultraviolet detection at 230nm were compared as methods
for the determination of iodide in the presence of other iodine species. Satisfactory results
were obtained from the potentiometric method provided the solution was first diluted ten-
fold with 5M sodium nitrate and external standards were used. Better reproducibility was,
however, achieved with high performance liquid chromatography provided precautions
were taken to prevent reduction of iodine to iodide in the mobile phase, for which
extraction of iodine with carbon tetrachloride prior to analysis was recommended. This
was the preferred method for automated analyses of iodine brines (iodide concentrations
of 30-40mg per litre).
Krishnamoorthy and Iyer [110] have reported a method for determining nanogram
levels of iodide in saline water samples containing a large excess of interfering chloride
ion. The anions are first bound to a strong base anion exchanger, from which the chloride
ion is readily eluted. The iodide is then eluted with 2M ammonium nitrate and the iodide
is determined based on its catalytic effect on the reduction of cerium(IV) by arsenic(III).
The method is claimed to have an accuracy comparable to that obtained by neutron
activation analysis.
3.19
Molybdate
3.19.1
Atomic absorption spectrometry
A limited amount of work has been carried out on the determination of molybdenum in
seawater by atomic absorption spectrometry [111-113] and graphite furnace atomic
absorption spectrometry [114]. In a recommended procedure a 50mL sample of seawater
at pH 2.5 is preconcentrated on a column of 0.5g
p
-aminobenzylcellulose, then the
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