Metals
9
argon/hydrogen (90:15.0) [5,6]. Absorption was maximal at 850-950 0c. Interference
effects from the matrix were reduced, and the sensitivity increased, by using trisodium phosphate as matrix modifier. The relative standard deviation was 3.5 % for
replicate determinations of 2.4 mg bismuth per kg river sediment.
2.7.4
Cadmium
Lum and Edgar [7] used a polarized Zeeman flame atomic absorption spectrometer to
determine traces of cadmium (and silver, see later) in chemical extracts of river
sediments. The detection limit was 0.1 mg kg- 1 based on a 0.2 g sample size and a
25 ml final solution volume.
In this method 0.2 g samples of the sediment were muffle ashed at 500°C for 3 h. A
separate 0.2 g sub-sample was dried in a forced air oven at 110°C for 24 h to determine moisture content. The ashed samples were carefully wetted with doubly distilled
water, transferred into PTFE beakers and 20 ml of freshly prepared aqua regia were
added. The digests were reduced nearly to dryness, 15 ml of hydrofluoric acid were
added and heating was continued until the samples were dry, care being taken to
avoid baking. Hydrochloric acid (15 ml) and 15 ml of doubly distilled water were then
added and the solutions were heated for 1 h to reduce the volume to about 15 ml.
After cooling, the volumes were made up to 25 ml in a calibrated flask. Cadmium was
evaluated in this solution at 228.8 nm using an air acetylene flame. In Table 2.2 the
Table 2.2
Accuracy of determination of cadmium by Zeeman atomic absorption spectrometry
(from [7])
Sample NBS SRM 1645
Expected concentration
Measured concentration
Recovery
Ilg l- 1
Ilg l- 1
%
River sediment
185
148 ± 0.2
80
National Institute for Environmental Studies, (Japan)
Reference pond sediment
6.1
5.7 - 5.8
93 - 95
NBS SRM 1633 organic free
coal flyash
6.2
6.3 ± 0.8
102
results obtained in applying this procedure to reference river sediment samples are
shown. The lower than expected cadmium recovery is in part due to its organic
content (1.7 % from extractable oil and grease, 10.7 % weight loss on ignition at
800°C). Higher recoveries were obtained with organic-free samples. Lum and Edgar
[7] carried out a five part sequential extraction procedure on 1 g dry weight samples
of sediment, (Table 2.3). Such extractions simulate, to a certain extent; various
environmental conditions to which sediments may be subjected. Although such schemes are not perfectly selective, they can provide valuable information on the mobility
and availability of elements in sediments.
Graphite furnace atomic absorption spectrometry has also been used for the determination of down to 0.04 mg kg- 1 of cadmium (and lead, see later) in river sediments.
9
argon/hydrogen (90:15.0) [5,6]. Absorption was maximal at 850-950 0c. Interference
effects from the matrix were reduced, and the sensitivity increased, by using trisodium phosphate as matrix modifier. The relative standard deviation was 3.5 % for
replicate determinations of 2.4 mg bismuth per kg river sediment.
2.7.4
Cadmium
Lum and Edgar [7] used a polarized Zeeman flame atomic absorption spectrometer to
determine traces of cadmium (and silver, see later) in chemical extracts of river
sediments. The detection limit was 0.1 mg kg- 1 based on a 0.2 g sample size and a
25 ml final solution volume.
In this method 0.2 g samples of the sediment were muffle ashed at 500°C for 3 h. A
separate 0.2 g sub-sample was dried in a forced air oven at 110°C for 24 h to determine moisture content. The ashed samples were carefully wetted with doubly distilled
water, transferred into PTFE beakers and 20 ml of freshly prepared aqua regia were
added. The digests were reduced nearly to dryness, 15 ml of hydrofluoric acid were
added and heating was continued until the samples were dry, care being taken to
avoid baking. Hydrochloric acid (15 ml) and 15 ml of doubly distilled water were then
added and the solutions were heated for 1 h to reduce the volume to about 15 ml.
After cooling, the volumes were made up to 25 ml in a calibrated flask. Cadmium was
evaluated in this solution at 228.8 nm using an air acetylene flame. In Table 2.2 the
Table 2.2
Accuracy of determination of cadmium by Zeeman atomic absorption spectrometry
(from [7])
Sample NBS SRM 1645
Expected concentration
Measured concentration
Recovery
Ilg l- 1
Ilg l- 1
%
River sediment
185
148 ± 0.2
80
National Institute for Environmental Studies, (Japan)
Reference pond sediment
6.1
5.7 - 5.8
93 - 95
NBS SRM 1633 organic free
coal flyash
6.2
6.3 ± 0.8
102
results obtained in applying this procedure to reference river sediment samples are
shown. The lower than expected cadmium recovery is in part due to its organic
content (1.7 % from extractable oil and grease, 10.7 % weight loss on ignition at
800°C). Higher recoveries were obtained with organic-free samples. Lum and Edgar
[7] carried out a five part sequential extraction procedure on 1 g dry weight samples
of sediment, (Table 2.3). Such extractions simulate, to a certain extent; various
environmental conditions to which sediments may be subjected. Although such schemes are not perfectly selective, they can provide valuable information on the mobility
and availability of elements in sediments.
Graphite furnace atomic absorption spectrometry has also been used for the determination of down to 0.04 mg kg- 1 of cadmium (and lead, see later) in river sediments.