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the controlling factor, however, one would expect a greater difference between well and
potable water than was observed. Similarly, for selenate the critical separation is from
sulphate, which is greatest in drinking water, but river and well water differ more in
sulphate content than well and potable water, in contrast to the calibration curves.
Table 12.7
Calibrate data for recycle determination of trace anions in water
Intercept, S
cm
−1
Slope, S
cm
−1
g
−1
Water
Detection limit,
µg
N
Selenate (3.0mmol L
−1
NaHCO
3
, 2.4mmol L
−1
Na
2
CO
3
, pH 9.72)
0.26±0.15
a
3.49 ± 0.30
a
Drinking (1)
0.21
6
Drinking (2)
0.20 ± 0.06
2.37 ± 0.26
0.18
10
Well
0.0II ±0.03
1.166 ±0.016
0.020
8
River
0.01 2 ±0.004
1.226 ±0.0 16
0.018
6
Selenite (3.0mmol L
−1
NaHCO
3
, 2.0mmol L
−1
Na
2
CO
3
, pH 9.24)
Drinking
−0.034±0.052
2.23 ±0.10
0.20
19
Well
−0.089±0.056
2.33 ±0.1 6
0.18
11
River
0.77 ± 0.25
1.63 ±0.25
1.2
13
Arsenate (2.5mmol L
−1
NaHCO
3
, 1.5mmol L
−1
Na
2
CO
3
, pH 9.56)
Drinking
0.024 ±0.10
0.83 ± 0.20
0.47
6
Well
−0.017±0.10
0.781 ±0.038
0.68
8
River
−0.03±0.09
0.902 ± 0.045
0.83
12
a
Standard deviation
Source: Reproduced with permission from the American Chemical Society [22]
12.2.3
Metal cyanide complexes
The cyanide ion in inorganic cyanides can be present as both complexed and free
cyanide. In order to study the chromatography of metal cyanides, Rocklin and Johnson
[23] prepared and assayed solutions of cadmium, zinc, copper, nickel, gold, iron and
cobalt cyanides. Table 12.8 lists the percentage of total cyanide detected.
The results suggest that the complex cyanides can be grouped into three categories
depending on the cumulative formation constant and stability of the complex. Category 1
includes the weakly complexed and labile cyanides Cd(CNO)
4
2−
(log β4=18.8) and Zn
(CN)4
2
−
(log β4=16.7). These complexes completely dissociate under the
chromatographic conditions used; the cyanide being indistinguishable from free cyanide.
Category 2 includes the moderately strong cyanide complexes Ni(CN)
4
2−
(log β4=31.3)
and Cu(CN)
4
3−
(log β4=30.0). Although the complexes are labile, they are retained on
the column and slowly dissociate during the chromatography. This slow dissociation
produces tailing which lasts for several minutes as the free cyanide elutes and is detected.
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