Chemistry Reference
In-Depth Information
10.19
Sulphite
10.19.1
Ion chromatography
Ion chromatography has been applied to the determination of sulphite in photographic
processing effluents [73].
Petrie
et al.
[31] applied ion chromatography to the determination of sulphite and
dithionite in mineral leachates.
The application of this technique is also discussed under multianion analysis in section
12.8.4.
10.20
Thiocyanate
10.20.1
Titration method
The application of this technique is discussed under multianion analysis in section
14.3.2.2.
10.20.2
Spectrophotometric method
In a method [74] for the determination of thiocyanate in the effluent from a film
processing unit, ferro and ferricyanides are first precipitated by the addition of zinc
sulphate. Zinc is then precipitated from the filtrate by adding sodium carbonate and
thiocyanate is determined in the final filtrate absorbtiometrically using ferric chloride.
Down to 1mg L
−1
thiocyanate can be determined.
Luthy
et al.
[75] have described a spectrophotometric method for the determination of
thiocyanate and cyanide in coal gasification waste waters. They showed that the copper
pyridine method with pre-extraction was applicable but that high concentrations of
carbonate and sulphide must first be removed from the sample.
Botto
et al.
[76] used p-phenylenediamine as the chromogenic reagent in the
spectrophotometric determination of thiocyanate and uncomplexed cyanide in waste
water.
10.20.3
Ion selective electrodes
Thiocyanate has been determined in waste water using a cyanide-selective electrode [77].
In this method thiocyanate is first converted to cyanogen bromide using bromine water.
Excess bromine is removed by the addition of phenol. The cyanogen bromide is then
converted to cyanide by the addition of sulphurous acid and then sodium hydroxide
added. Cyanide is then estimated using the cyanide selective electrode:
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