10
River and Stream Sediments
Table 2.3
Sequential chemical extraction procedure carried out on 1 g dry weight of lake sediment
(from [7])
Extractant
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5h @ 20°C)
1 moll-I NH 2 0H·HCI - 25 %
CH 3 COOH
(2 h @ 20°C)
H 2 0 2 , pH 2. (5 h @ 90°C)
1.2 moll-I CH 3 COONH 4 - 20 %
HN0 3
Aqua Regia - HF - HCI - H 2 0 2
(total cadmium content 3.5 - 8.0 mg kg-I)
In extract
Readily exchangeable ions
Carbonate bound surface - oxide
bound ions
Ions bound to Fe-Mn oxides
% of total cadmium
17 ± 6
31 ± 10
34 ± 7
Organically and sulphide bound ions 12 ± 5
Ions bound to the residual phase
6 ± 3
Table 2.4 Cadmium in river sediments by open beaker and Teflon-lined bomb digestions
(from [8])
Digestion conditions
Vessel
Reagent
Time (h)
Temperature °c
NBS SRM 1645 river sediment
10.2 ± 1.5 mg kg-I nominal
cadmium
River Sediment
2
3
4
Carbon
content % Teflon lined bomb
Teflon open beaker
0.32
1.29
2.84
7.20
HF (10 ml), HN0 3 (4 ml) HF (10 mI), HN0 3 (10 mI)
HCI0 4 (1 mI)
HCI0 4 (5 ml)
1
U
140
mgkg-I
9.55 ± 0.22
0.08 ± 0.01
0.23 ± 0.01
0.17 ± 0.01
1.22 ± 0.12
150
mgkg- I
9.30 ± 0.10
0.08 ± 0.01
0.21 ± 0.04
0.18 ± 0.01
1.22 ± O.lO
Sakata and Shimoda [8] have described a simple and rapid method in which 0.5 g
sediment is digested for 1 hat 140°C with a mixture of 10 ml hydrofluoric acid, 4 ml
nitric acid and 1 ml perchloric acid in a Teflon lined bomb prior to measurement by
graphite furnace atomic absorption spectrometry at 228.8 nm using an automatic
sampling device. After digestion,S g of boric acid is added to the solution to dissolve
precipitated metal fluorides. Sodium and potassium interference is overcome by the
addition of 1 % ammonium sulphate matrix modifier. Table 2.4 shows cadmium
contents obtained by this procedure compared to those obtained in a more lengthy
open beaker digestion for a range of river sediments containing increasing amounts of
carbon, and for an NBS reference sample. The two methods have practically"the same
precision, there being no significant difference at the 95 % confidence level in the
results between the two methods in samples containing between 0.32-7.2 % of carbon.
A good recovery (94 %) was obtained for the NBS reference sediment.
Table 2.5 shows the beneficial effect on cadmium recovery of incorporating an
ammonium sulphate matrix modifier in the final solution to overcome interference
River and Stream Sediments
Table 2.3
Sequential chemical extraction procedure carried out on 1 g dry weight of lake sediment
(from [7])
Extractant
0.75 moll-I LiCI - 0.25 moll-I CsCI
-60 % MeOH (10 min @ 20°C)
1 moll-I CH 3 COONa, pH 5.0
(5h @ 20°C)
1 moll-I NH 2 0H·HCI - 25 %
CH 3 COOH
(2 h @ 20°C)
H 2 0 2 , pH 2. (5 h @ 90°C)
1.2 moll-I CH 3 COONH 4 - 20 %
HN0 3
Aqua Regia - HF - HCI - H 2 0 2
(total cadmium content 3.5 - 8.0 mg kg-I)
In extract
Readily exchangeable ions
Carbonate bound surface - oxide
bound ions
Ions bound to Fe-Mn oxides
% of total cadmium
17 ± 6
31 ± 10
34 ± 7
Organically and sulphide bound ions 12 ± 5
Ions bound to the residual phase
6 ± 3
Table 2.4 Cadmium in river sediments by open beaker and Teflon-lined bomb digestions
(from [8])
Digestion conditions
Vessel
Reagent
Time (h)
Temperature °c
NBS SRM 1645 river sediment
10.2 ± 1.5 mg kg-I nominal
cadmium
River Sediment
2
3
4
Carbon
content % Teflon lined bomb
Teflon open beaker
0.32
1.29
2.84
7.20
HF (10 ml), HN0 3 (4 ml) HF (10 mI), HN0 3 (10 mI)
HCI0 4 (1 mI)
HCI0 4 (5 ml)
1
U
140
mgkg-I
9.55 ± 0.22
0.08 ± 0.01
0.23 ± 0.01
0.17 ± 0.01
1.22 ± 0.12
150
mgkg- I
9.30 ± 0.10
0.08 ± 0.01
0.21 ± 0.04
0.18 ± 0.01
1.22 ± O.lO
Sakata and Shimoda [8] have described a simple and rapid method in which 0.5 g
sediment is digested for 1 hat 140°C with a mixture of 10 ml hydrofluoric acid, 4 ml
nitric acid and 1 ml perchloric acid in a Teflon lined bomb prior to measurement by
graphite furnace atomic absorption spectrometry at 228.8 nm using an automatic
sampling device. After digestion,S g of boric acid is added to the solution to dissolve
precipitated metal fluorides. Sodium and potassium interference is overcome by the
addition of 1 % ammonium sulphate matrix modifier. Table 2.4 shows cadmium
contents obtained by this procedure compared to those obtained in a more lengthy
open beaker digestion for a range of river sediments containing increasing amounts of
carbon, and for an NBS reference sample. The two methods have practically"the same
precision, there being no significant difference at the 95 % confidence level in the
results between the two methods in samples containing between 0.32-7.2 % of carbon.
A good recovery (94 %) was obtained for the NBS reference sediment.
Table 2.5 shows the beneficial effect on cadmium recovery of incorporating an
ammonium sulphate matrix modifier in the final solution to overcome interference