Thesis for the Degree of Doctor of Philosophy - DTU Orbit

9). The results shows that iodine present in solution was nearly quantitatively removed (around 2.5-7.6 % of
the total iodine remains in the water phase after batch experiment, Table 9, experiment numbers 3 and 4)
even when the concentration of natural organic iodine compounds extracted from soils and seaweed were
added to the fresh water (Table 9) increase significantly. By contrast when using a mixture of
K2S2O8/NaClO as an oxidant, relatively high (30 - 40%) amount of iodine remains in the water phase after
the batch experiment (Table 10, experiments numbers 9 and 10).
Due to the low amount of iodine that remains in the water phase after the batch experiments (Table 9,
experiments numbers 3-6) we conclude that the oxidation of iodine organic matter by using K2S2O8
followed by reduction of iodine species and precipitation with silver nitrate can be a potential method for
determination of total iodine in freshwater samples. Because more samples can be treated simultaneously,
the method is rapid and very suitable for field use if needed.
Table 9 Main protocols for oxidation of iodine organic matter in water samples by using K2S2O8 for
quantification of total iodine. The volume of water was 200ml in all experiments. The experiments were
conducted at room temperature. All forms of iodine resulted after destruction of organic iodine were
converted to iodide by adding 1mL of 1M K2S2O5 at pH 1-2 with 3M HNO3 and finally precipitated as
silver iodide by adding 1-2 mL of 1M AgNO3. After 30’ stirring and centrifugation at 3000 x g for 30’ the
silver iodide precipitate is separated from water.
Experiment
number
Experiment setting
127 I
concentration
in studied
sample (ppb)
The fraction of 127 I that
remains in the water
phase after batch
experiment (%)
1 0.2 g K2S2O8/2 mL of iodine NOM extracted from seaweed
with water/sample pH 6-7/2h stirring
107.2 9.8
2 0.2 g K2S2O8/4 mL of iodine HSs extracted from soil with 5%
TMAH/sample pH 10-11/2h stirring
43.6 19.4
3 0.5 g K2S2O8/3 mL of iodine NOM extracted from seaweed with
water/sample pH 6-7/2h stirring
100.9 2.5
4 0.5 g K2S2O8/3 mL of iodine HSs extracted from soil with 5%
TMAH/sample pH 10-11/2h stirring
47.1 7.6
5 1 g K2S2O8/4 mL mL of iodine NOM extracted from seaweed
with water/sample pH 6-7/2h stirring
145.1 5.1
6 1 g K2S2O8/4 mL of iodine HSs extracted from soil with 5%
TMAH/sample pH 10-11/2h stirring
49.80
10.0
7 0.5 g K2S2O8/2 mL of iodine NOM extracted from seaweed with
water/sample pH 6-7/17h stirring
71.4 13.8
8 1 g K2S2O8/2 mL of iodine NOM extracted from seaweed with
water/sample pH 6-7/17h stirring
72.0 11.9
NOM – natural organic matter; HSs – humic substances; TMAH - tetramethylammonium hydroxide;
However, direct precipitation of total iodine (without oxidation of iodine organic matter) from freshwater as
silver iodine was also performed (Table 10, experiments numbers 11-14). As a result, the relative amount of
total iodine was determined to be 8-15% in the filtrate after the batch experiment (Table 10, experiments
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