Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 311

2.94.5 Polarography
Differential pulse polarography has been used [823] to determine sulphide in non saline
waters. Java et al. [824] preconcentrated sulphide at concentrations ranging from 0 to
40µg L −1 on to a silver electrode. The electrode was preconditioned at a constant negative
potential of 1.2V. The open circuit mode of the potentiostat was selected and the sample
stirred for 10min, after which the current measurement mode was selected immediately.
Peak currents or charges passing were compared with those obtained from standard
solutions. The procedure was precise and reliable with a similar sensitivity to and better
selectivity than conventional cathodic-stripping voltammetry. Sulphide at µg L −1 levels
was determined in non saline water samples, with a precision of 2%.
2.94.6 Ion selective electrodes
Studies on sulphide selective electrodes have been reported by various workers [825-
832].
Al Hitti et al. [827] carried out direct potentiometric titration of sulphide sulphur in
non saline water using standard cadmium sulphate solution as titrant and an electrode
comprising silver deposited on to a carbon reed. The sensitivity of this procedure is 2mg
L −1 sulphide.
Guterman and Ben-Yaakov [829] determined total dissolved sulphide in the pH range
7.5-11.5 by ion selective electrodes. Their instruments combine a sulphide ion activity
electrode and pH glass electrode to produce a pH-independent output voltage that is
proportional to total dissolved sulphide concentration.
Gulens [830] developed a portable monitor for measurement of total dissolved sulphide
in non saline water based on the glass/sulphide electrode couple.
Tse et al. [831] used an electrode coated with electrochemically deposited N, N I , N II ,
N III tetramethyl tetra 3, 4 pyridimoporphydazino cobalt(I) for the determination of
sulphide ions.
2.94.7 Ion chromatography
Bond et al. [280] used ion chromatography to determine sulphide and cyanide in non
saline waters. Peschet and Tinet [281] used this procedure to co-determine sulphide,
hypochlorite and cyanide in ground waters.
Goodwin et al. [833] determined traces of sulphide in turbid waters by gas dialysis ion
chromatography. Sulphide quantitation was achieved in zinc preserved samples by this
technique with a 1.9µg L −1 detection limit, a precision of 0.64µg L −1 and a recovery of
98-101%.
Haddad and Heckenberg [834] converted trace levels of sulphide in environmental
samples to a stable product by reaction with N,N ′ -dimethyl-p-phenylenediamine to form
methylene blue, thus avoiding the major problems normally associated with ion exchange
methods. Optimal chromatographic conditions were selected and the effects of various
analytical parameters and interferences established. Ferrocyanide and ferricyanide at
10mg L −1 levels, which normally presented a major problem for spectrophotometric