The determination of ammonia in condensed steam and boiler feed-water with a potentiometric ammonia probe

An electrochemical probe, based on the diffusion of gas across a polymer membrane, has been investigated for possible use in determining ammonia in condensed steam and boiler feed-water. A simple method that gives results of adequate precision and accuracy has been developed; the standard deviations at concentrations of 1·0, 0·5 and 0·1 µg ml–1 were 0·05, 0·01 and 0·005 µg ml–1, respectively. Results obtained by the method described and by the ammonium-sensitive glass electrode method differed by a maximum of 6 per cent. and an average of only 0·3 per cent. Of the substances to be expected in feed-water, only cyclohexylamine and octadecylamine had a significant effect. For routine purposes this method is preferred to the more precise, but more time consuming, indophenol blue method. The principal advantage of this probe over the ammonium-sensitive glass electrode is that no correction is required in the presence of alkali metal ions.