Anions in sewage effluent - Determination of Anions in Natural and Treated Waters - page 581

vapour equilibrium in a closed flask, and the concentration of hydrogen sulphide vapour
in the air space is determined by conventional gas analyser. The pH of the solution is
adjusted to 5.0 by means of a buffer solution and the ionic strengths of samples and
standards are maintained at a constant level by the strong electrolytes incorporated into
this solution. The above method determines undissociated hydrogen sulphides,
hydrosulphide and sulphide ions. To determine total sulphide including above plus other
compounds liberating hydrogen sulphide from a cold solution containing 0.5M
hydrochloric acid, follow the above procedure using 50ml acid chloride solution instead
of buffer solution.
The comparative freedom of interference from other sulphur-containing anions is of
particular note. Sulphite, metabisulphite and thiosulphate do not interfere significantly at
100-fold excess, detergents depress the recovery of sulphide at 100-fold excess but do not
interfere significantly at 10-fold excess.
9.9.2 Ion selective electrode
Glaister et al. [17] studied three sulphide ion selective electrodes in cascade flow and
flow-through modes to investigate carrier stream, sample size and flow rate parameters in
the analysis of sulphide in sewage effluents. Results were compared with those obtained
by direct potentiometry. The electrodes were successfully used as detectors of sulphide
during flow injection analysis and the presence of ascorbic acid in the standard
antioxidant buffer minimised deleterious effects of hydrogen peroxide in the samples.
Both the cascade flow and flow-through modes of electrodes yielded sulphide
concentrations similar to those from colorimetric methods.
References
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3 Department of the Environment/National Water Council Standing Committee of
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materials. Chloride in waters, sewage and effluents (1982).
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7 Rea, R.E. Water Pollution Control , 78 , 139 (1979).
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(1970).
11 Petts, K.W. Water Research Centre, Stevenage, UK. Technical Memorandum No.
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12 Department of the Environment/National Water Council Standing Committee of
Analysts. HMSO, London. Methods for the examination of water and associated