Effect of surfactants on the determination of nitrate in stream waters by using a nitrate ion-selective electrode

Abstract

Nitrate-nitrogen in stream waters containing anionic surfactants was determined with a nitrate ion-selective electrode. The results with 22 stream waters agreed well with those obtained by spectrophotometry. Nitrite, hydrogen carbonate and chloride interference were removed by the addition of sulphamic acid, sulphuric acid and silver sulphate, respectively. The interference from anionic surfactants was no problem provided its concentration was lower than 1 mg l^–1 as dodecylbenzenesulphonate (DBS). The error caused by DBS depends on its concentration and can be mostly eliminated by the addition of a cationic surfactant such as cetyltrimethylammonium bromide. An anomalous response behaviour in the presence of some cationic surfactants was observed and is discussed in relation to their extractability as nitrate salts.