Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 158

Spring 7.38 27.2 26.9 27.0
Creek 6.53 27.2 27.1 26.2
Lake 7.85 27.2 26.3 23.4
Pond 8.57 27.2 23.1 20.6
a Expected concentration is equal to that added as sodium cyanide plus that present in the effluent
portion; all values adjusted for pH and temperature
Source: Reproduced with permission from the American Chemical Society [246]
Sulphide at concentrations of 1.0mg L −1 Na 2 S-S extensively interfered with the
determination of hydrogen cyanide. Since it was observed that such a concentration will
only have minimal effect on the direct colorimetric procedure for cyanide determination,
the interference process must occur in the test solution itself. Possibly sulphide oxidation
products, especially polysulphides, react with cyanide to produce thiocyanate. Therefore,
sulphide should be removed from a sample as soon as possible after collection to prevent
its potential interaction with cyanide. Recommended procedures for sulphide removal
suggest the addition of either lead or cadmium salts.
In Table 2.16 are shown some results obtained in applying the diffusion procedure to
several spiked non saline water samples.
Montgomery et al. [250] determined free hydrogen cyanide in river water by a method
based on extraction of cyanide ion from water with 1:1:1 trichloroethane, then re-
extraction of cyanide in aqueous pyrophosphate solution. After the extraction of
hydrogen cyanide into sodium pyrophosphate solution it is treated with saturated aqueous
bromine, sodium arsenite and p-phenylene diamine and determined
spectrophotometrically at 508nm. Less than 0.01mg L −1 of hydrogen cyanide can be
detected.
Aoki et al. [251] determined cyanide in non saline water, in the presence of heavy
metals, based on its separation as hydrogen cyanide by passage through a microporous
poly(tetrafluoroethylene) membrane and reaction with hypochlorite. Absorption was
measured at the λ max for hypochlorite (290nm). The relative standard deviation was 1.9%
at the 1×10 −6 M cyanide level.
2.23.2 Spectrofluorometric method
1,10 Phenanthroline complexes
Yin and Ho [252] described a method for free cyanide in non saline water based on
released fluorescence of a dissociated ternary complex. A cationic ternary silver complex
formed by the reaction of tetrabromofluorescein (TBF) with silver 1,10-phenanthroline at
pH 3-8, dissociated in the presence of cyanide to give the highly fluorescent anion, the
intensity of which was directly proportional to cyanide concentration. Interference by
magnesium, calcium and lead(II) ions found in water were masked by chelation with
EDTA. Lead acetate was used to precipitate sulphide; other common anions, such as
chloride, sulphate and nitrate, did not interfere. The detection limit was 0.02µg L −1
cyanide.