Chemistry Reference
In-Depth Information
As the results presented in Table 12.8 demonstrate, the tailing and the non-quantitative
recovery of cyanide preclude the use of direct injection to determine total cyanide in
samples containing copper and nickel.
Table 12.8
Percentage of total cyanide in metal complexes determined as 'free' cyanide
log
β
1
Metal complex
%
Cd(CNO)
4
2-
18.8
102
Zn(CN)
4
2-
16.7
102
Ni(CN)
4
2-
31.3
81
Cu(CN)
4
3-
30.3
52
Cu(CN)
3
2-
28.6
42
Cu(CN)
2
-
24.0
38
Au(CN)
2
-
38.3
0
Fe(CN)
6
3-
42
0
Co(CN)
6
3-
64
0
Source: Reproduced with permission from the American Chemical Society [23]
These samples may be analysed after acid distillation and caustic trapping. The cyanide
in the caustic solution can then be determined by ion chromatography with
electrochemical detection.
Category 3 includes those cyanides which are inert and therefore totally undissociated,
such as Au(CN)
2
−
(log β
2
=38.3), Fe(CN)
6
3−
(log β
6
= 42) and Co(CN)
6
3−
(log β
6
=64).
No free cyanide was detected for these complexes. Although these complexes do not
elute under the chromatographic conditions used, they can be eluted and determined by
using different chromatographic conditions and conductivity detection.
Samples containing both free cyanide (or weakly complexed cyanide) and strongly
complexed cyanide can be analysed for free cyanide by direct injection. The
determination of total cyanide (both free and strongly complexed) requires distillation of
the sample with caustic trapping.
Determinations of anions in non saline water are disturbed by the inevitable presence
of humic substances which are strongly adsorbed on the ion chromatographic column.
Marko Varga
et al.
[14] found that a cleanup column prior to the separation column,
packed with a chemically bonded amine material (Nucleosil 5 NH2) was effective in
removing interfering humic substances. No influence was found from humic substances
in concentrations up to 45µg L
−1
on ion chromatographic analysis of nitrate and sulphate
(10-100mg L
−1
) after passage through the clean up column.
A short column packed with an amine bonded polymer (weak anion exchange
material) connected prior to the anion separation column was found to be very effective
for the selective removal of humic substances prior to anion separation by ion
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