Metals
15
Lum and Edgar [7] carried out a five part sequential extraction procedure on 1 g
dry weight Moira Lake sediment (Table 2.8), showing the distribution of different
forms of silver in the sediment. Regardless of core depth, most of the silver is
organically or sulphide bound or bound to the residual phase.
2.1.71
Selenium
The inductively coupled argon plasma emission spectrometric method described
above for the determination of arsenic in river sediments [4] has also been applied to
the determination of selenium down to 0.03 !lg I-I in the solution obtained following
fusion of the sediment with solid sodium hydroxide in a zirconium crucible. A
reference sample with a nominal selenium content of 0.4 mg kg- I gave a value of
0.49 ~g kg- I by this method.
Cutter [2] has described a selective hydride generation technique for the determination of total selenium in oxidative digests of river sediments.
2.1.12
Tin
Long-Zhu [18] has described a graphite furnace atomic absorption spectrometric
method for the determination of down to 2.5 mg kg- I of tin in river sediments.
Samples are decomposed in a Teflon-lined pressure vessel using perchloric, nitric
and hydrofluoric acids. A mixture of ascorbic acid and iron is used as a matrix
modifier. In the presence of the matrix modifier, the char temperature for tin can be
raised to 1100 °c and the interferences caused by perchloric acid and sample matrices
are greatly reduced. A good recovery is obtained. Between 90 and 104 % of the tin is
recovered.
In this procedure, 0.1 g of sediment is transferred to a Teflon beaker and digested
with 0.5 ml 0.01 mol 1-1 nitric acid to moisten the sample then 1 ml concentrated nitric
acid. After leaving for l2 h, 1 ml 72 % perchloric acid and 3 ml concentrated hydrofluoric acid are added and the container transferred to a steel bomb and heated for 6 h at
190°C. The contents of the beaker are then heated to near dryness at 140 °c and then
boiled with sufficient 0.2 % oxalic acid solution. Successively, 20 j.t.l of sample solution
prepared as above and 10 j.t.l of 400 mg 1-1 iron solution are injected, it is then dried at
110°C for 40 s, the residue charred at 1000 °c for 30 s, then atomized at 2400 °c for 5 s
at "maximum power" and "argon flow interrupted". Tin absorbance is measured at the
resonance line of 286.3 nm. Finally, the tube is cleaned at 2700 °c for 3 s.
A reference sediment NBS SRM 1645 (nominal 313 ± 9 mg kg- I tin) gave a value of
363 mg kg- I by this method.
2.1.13
Multi-Element Analysis
Much of the published work is concerned with the determination of a range of
elements rather than single elements as discussed below. Multi-element analysis is
discussed below under separate analytical techniques.
15
Lum and Edgar [7] carried out a five part sequential extraction procedure on 1 g
dry weight Moira Lake sediment (Table 2.8), showing the distribution of different
forms of silver in the sediment. Regardless of core depth, most of the silver is
organically or sulphide bound or bound to the residual phase.
2.1.71
Selenium
The inductively coupled argon plasma emission spectrometric method described
above for the determination of arsenic in river sediments [4] has also been applied to
the determination of selenium down to 0.03 !lg I-I in the solution obtained following
fusion of the sediment with solid sodium hydroxide in a zirconium crucible. A
reference sample with a nominal selenium content of 0.4 mg kg- I gave a value of
0.49 ~g kg- I by this method.
Cutter [2] has described a selective hydride generation technique for the determination of total selenium in oxidative digests of river sediments.
2.1.12
Tin
Long-Zhu [18] has described a graphite furnace atomic absorption spectrometric
method for the determination of down to 2.5 mg kg- I of tin in river sediments.
Samples are decomposed in a Teflon-lined pressure vessel using perchloric, nitric
and hydrofluoric acids. A mixture of ascorbic acid and iron is used as a matrix
modifier. In the presence of the matrix modifier, the char temperature for tin can be
raised to 1100 °c and the interferences caused by perchloric acid and sample matrices
are greatly reduced. A good recovery is obtained. Between 90 and 104 % of the tin is
recovered.
In this procedure, 0.1 g of sediment is transferred to a Teflon beaker and digested
with 0.5 ml 0.01 mol 1-1 nitric acid to moisten the sample then 1 ml concentrated nitric
acid. After leaving for l2 h, 1 ml 72 % perchloric acid and 3 ml concentrated hydrofluoric acid are added and the container transferred to a steel bomb and heated for 6 h at
190°C. The contents of the beaker are then heated to near dryness at 140 °c and then
boiled with sufficient 0.2 % oxalic acid solution. Successively, 20 j.t.l of sample solution
prepared as above and 10 j.t.l of 400 mg 1-1 iron solution are injected, it is then dried at
110°C for 40 s, the residue charred at 1000 °c for 30 s, then atomized at 2400 °c for 5 s
at "maximum power" and "argon flow interrupted". Tin absorbance is measured at the
resonance line of 286.3 nm. Finally, the tube is cleaned at 2700 °c for 3 s.
A reference sediment NBS SRM 1645 (nominal 313 ± 9 mg kg- I tin) gave a value of
363 mg kg- I by this method.
2.1.13
Multi-Element Analysis
Much of the published work is concerned with the determination of a range of
elements rather than single elements as discussed below. Multi-element analysis is
discussed below under separate analytical techniques.