Chemistry Reference
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is calculated from the difference between the peak heights of 4, 6-dibromopiazselenol in
these chromatograms. The amounts and oxidation states of selenium in river water in
Japan are shown in Table 2.46. The total amount of selenium in river water varied
greatly, eg from 16 to 230ng L
−1
.
Table 2.46
Determination of selenium in river water
Sample
a
ng L
−1
Se(
−II
, O)
Se(IV)
Se(VI)
Total Se
Yoshii River, Okayama
Pref. Feb 5, 1979
12
16
202
231
Takahashi River, Okayama
Pref Feb 5, 1979
5
4
7
16
Asahi River, Okayama
Pref Feb 5, 1979
11
<2
9
20
Asahi River, Okayama
Pref Feb 17, 1979
11
2
3
16
a
Samples contained 1mL
−1
of concentrated hydrochloric acid
Source: Reproduced with permission from the American Chemical Society [673]
2.90.8
Sample preservation
Cheam and Agemian [681] studied the preservation and stability of inorganic selenium
compounds at µg L
−1
levels in non saline water samples. They adopted the use of
sulphuric acid as the preserving medium as this was found not to interfere with the
hydride generation method they adopted for the determination of arsenite and arsenate.
They found that the use of polyethylene sample containers and pH adjustment to 1.5
(with 0.2 vol% sulphuric acid) provided optimal conditions for the preservation of
samples for periods of up to 125 days. Storage at 4°C also preserves samples effectively
over the same time span.
2.90.9
Preconcentration
The application of preconcentration to selenate and selenite is discussed in sections
15.1.9 and 15.1.13.
2.91
Silicate
2.91.1
Spectrophotometric methods
Spectrophotometric methods for the determination of silicon in water are based on the
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