Chemistry Reference
In-Depth Information
In a dried reaction tube is placed 10ml of sample solution (pH 5-8) containing less
than −5µg of cyanide and free from sulphide and thiocyanate ions. 3.0ml of potassium
dihydrogen phosphate solution (1mol L
−1
) and 0.2ml of 1% (w/v) chloramine-T solution
are added, the tube stoppered and shaken. After 1-2min, 5.0ml of isonicotinic acid-
barbituric acid reagent is added and the tube stoppered again,
Table 8.9
Comparison of effect of diverse ions on the determination of 2.0µg CN
−
/10ml
by the isonicolinic acid-barbituric acid method
Ion
Added as
Amount added
(µg/10ml)
CN
−
found
(µg)
Error
(µg)
Cl
−
NaCl
1000
2.0
0.0
NO
2
−
NaNO
2
1000
1.9
−0.1
NO
3
−
KNO
3
1000
2.0
0.0
SO
3
2−
Na
2
SO
3
100
1000
2.0
0.0
SO
4
2−
Na
2
SO
4
1000
2.0
0.0
CH
3
COO
−
CH
3
COONa.
3
H
2
O
100
2.0
0.0
OCN
KOCN
1000
1.9
−0.1
S
2−
Na
2
S.9H
2
O
1
10
100
1000
2.0
2.0
0.9
0.0
0.0
−1.1
SCN
−
KSCN
2
5
2.9
4.3
+0.9
+2.3
Fe
3+
FeCl
3
100
2.1
+0.1
Fe(CN)
6
4−
K
4
[Fe(CN)
6
] 3H
2
O
100
2.0
0.0
Fe(CN)
6
3−
K
3
[Fe(CN)
6
]
10
100
2.0
0.0
Source: Reproduced with permission from Gordon AC Breach [27]
keeping the mixture at 25°C for 15min. The absorbance is measured at 600nm against a
reagent blank.
T
he effect of diverse ions on the determination of 2mg L
−1
cyanide by the above
method is shown in Table 8.9. A large amount of sulphide caused a negative error and
1mg of sulphide did not develop colour. In the pyrazolone method, sulphite and
ferricyanide also led to a negative error. Thiocyanate led to a significant positive error
when sulphide or thiocyanate ions were present in a sample solution, and a suitable
pretreatment is necessary for the removal.
The large positive error caused by thiocyanate suggested that the method could be used
Search WWH ::
Custom Search