The determination of trace amounts of sulphide in condensed steam with NN-diethyl-p-phenylenediamine

A sensitive colorimetric method has been developed for the determination of trace amounts of sulphide in condensed steam. For precise work the colour produced by NN-diethyl-p-phenylenediamine in the presence of iron(III) ions is measured spectrophotometrically covering the range 0·5 to 100 µg of sulphide-sulphur; the standard deviations at the 100 and 1·0-µg levels are about 3 and 0·08 µg, respectively. Reasonably accurate results over the range 0·5 to 25 µg of sulphide-sulphur can be obtained “on site” by a simple visual titration of a reference solution with a methylene blue solution. The NN-diethyl-p-phenylenediamine was shown to be superior to the dimethyl homologue normally used, and its use does not appear to have been reported previously. Methods of sampling and the effect of sulphite are also discussed.