Metals
11
Table 2.5
Effect of matrix modifier on the determination of cadmium (from [8])
Element
mg kg- 1 of sediment
Silicon
1000
Aluminium
500
Iron
500
Sodium
200
Potassium
200
Calcium
200
Titanium
100
Manganese
100
Cadmium recovery %
Without matrix
modifier
90
75
93
55
91
81
103
88
With matrix
modifier
102
108
104
95
98
92
99
98
effects. In the absence of the matrix modifier, the average recovery of cadmium from a
river sediment was 44.5 %, increasing to 100 % when the modifier was used.
2.7.5
Chromium
Pankow et al. [9] determined total chromium in river sediments. The samples were
dried on a hot plate, approximately 1 g of the dry material was weighed out and acid
washed with 25 ml of 1 mol 1-1 nitric acid (to effect a removal of surface-bound Cr),
and the acid wash fIltered through (previously acid-washed) medium speed fIlter
paper. The fIltrate (acid wash) was collected, and analyzed by atomic absorption
spectrometry using the method of standard addition. The acid washed sediment was
then redried, weighed, and placed in a 50 ml capacity teflon beaker. Then 15 ml
concentrated hydrofluoric acid and 15 ml concentrated nitric acid were added to each
sample, and then volatilized under the infrared lamps. This addition and subsequent
volatilization of acids was performed for a total of four times to ensure the complete
destruction of the sediments. After the fourth cycle, the brown residue which remained was dissolved in enough 1 mol 1-1 nitric acid to total 25 ml and then fIltered
through acid washed, medium speed fIlter paper. The average recovery achieved in
the analysis of spiked sediment samples indicated an average recovery of 97 % with a
precision of ± 4 % relative. Chromium contents down to 0.5 mg kg- 1 could be determined in river sediments by this method.
Scott [IO] has discussed the cause and control of chromium losses during nitric
acid-perchloric acid oxidation of river sediments.
2.7.6
Copper
Potentiometric stripping analysis has been used to determine down to 3 mg kg- 1 of
copper (and lead, see later) in river and estuarine sediments [11] with a precision of
3.9 - 4.5 %.
This system has three electrodes - a glassy carbon cathode, a saturated calomel
reference electrode, and a platinum counter electrode. The first step in the determination of metal ions in a sample solution is the electrochemical formation of a mercury
11
Table 2.5
Effect of matrix modifier on the determination of cadmium (from [8])
Element
mg kg- 1 of sediment
Silicon
1000
Aluminium
500
Iron
500
Sodium
200
Potassium
200
Calcium
200
Titanium
100
Manganese
100
Cadmium recovery %
Without matrix
modifier
90
75
93
55
91
81
103
88
With matrix
modifier
102
108
104
95
98
92
99
98
effects. In the absence of the matrix modifier, the average recovery of cadmium from a
river sediment was 44.5 %, increasing to 100 % when the modifier was used.
2.7.5
Chromium
Pankow et al. [9] determined total chromium in river sediments. The samples were
dried on a hot plate, approximately 1 g of the dry material was weighed out and acid
washed with 25 ml of 1 mol 1-1 nitric acid (to effect a removal of surface-bound Cr),
and the acid wash fIltered through (previously acid-washed) medium speed fIlter
paper. The fIltrate (acid wash) was collected, and analyzed by atomic absorption
spectrometry using the method of standard addition. The acid washed sediment was
then redried, weighed, and placed in a 50 ml capacity teflon beaker. Then 15 ml
concentrated hydrofluoric acid and 15 ml concentrated nitric acid were added to each
sample, and then volatilized under the infrared lamps. This addition and subsequent
volatilization of acids was performed for a total of four times to ensure the complete
destruction of the sediments. After the fourth cycle, the brown residue which remained was dissolved in enough 1 mol 1-1 nitric acid to total 25 ml and then fIltered
through acid washed, medium speed fIlter paper. The average recovery achieved in
the analysis of spiked sediment samples indicated an average recovery of 97 % with a
precision of ± 4 % relative. Chromium contents down to 0.5 mg kg- 1 could be determined in river sediments by this method.
Scott [IO] has discussed the cause and control of chromium losses during nitric
acid-perchloric acid oxidation of river sediments.
2.7.6
Copper
Potentiometric stripping analysis has been used to determine down to 3 mg kg- 1 of
copper (and lead, see later) in river and estuarine sediments [11] with a precision of
3.9 - 4.5 %.
This system has three electrodes - a glassy carbon cathode, a saturated calomel
reference electrode, and a platinum counter electrode. The first step in the determination of metal ions in a sample solution is the electrochemical formation of a mercury