Anions in wastewaters - Determination of Anions in Natural and Treated Waters - page 565

water and waste waters. Compressed nitrogen is bubbled through the sample to displace
hydrogen sulphide, which is collected in a glass-bead concentration column and
measured colorimetrically.
The application of this technique is discussed under multianion analysis in section
14.2.3.3.
8.21.2 Cathodic stripping voltammetry
Xi et al. [107] report that a cathodic stripping oscillographic polarography method for
determining trace sulphide in wastewater has recoveries ≥ 94% for 10-560µg L −1 S 2−
and a linear relationship between current peak height and sulphide concentration over the
range of 5pg L −1 to 5mg L −1 . The anions chloride, bromide, iodide, phosphate, sulphate
and thiocyanate do not interfere.
8.21.3 Ion selective electrodes
Both sulphide [108] and iodide-selective [109] electrodes have been used to determine
sulphide in waste water. Papp and Havas [108] used a sulphide ion selective electrode as
an indicator electrode in the potentiometric titration of sulphide with mercuric chloride.
Novkirishka et al. [109] used an iodide-selective electrode in an indirect potentiometric
titration procedure to determine sulphide in industrial waste waters. Sulphide is first
precipitated as cadmium sulphide by addition of cadmium acetate in an alkaline medium.
The isolated cadmium sulphide is dissolved in excess standard iodine solution and excess
iodine estimated by potentiometric titration using the iodide selective electrode.
8.21.4 Ion chromatography
Goodwin et al. [110] determined trace sulphides in turbid waters by a gas dialysis/ion
chromatographic method. The sulphide is converted to hydrogen sulphide which is then
isolated from the sample matrix by diffusion through a gas dialysis membrane and
trapped in a dilute sodium hydroxide solution. A 200µL portion of this solution is
injected into an ion chromatograph for determination with an electrochemical detector.
Detection limits were ≥ 1.9ng/mL −1 .
8.21.5 Ion interaction chromatography
Haddad and Heckenberg [111] determined sulphide in wastewaters by reversed-phase
ion-interaction chromatography following precolumn reaction of sulphide with N,N -
dimethyl- p -phenylenediamine giving a detection limit of 0.8µg L −1 .
8.22 Sulphite
8.22.1 Spectrophotometric method
The application of this technique is discussed under multianion analysis in section