Ammonium detection by formation of colored zebra-bands in a detecting tube

Ammonium ion was colorized by means of a diazo coupling reaction with 2-phenylphenol, where the color development reaction was conducted within 3 min by using boric acid as a catalyst. The resulting colored solution (0.5 ml) was supplied by suction to a detecting tube consisting of a nonwoven fabric test strip (2 mm wide, 1 mm thick, 150 mm long) impregnated with benzylcetyldimethylammonium chloride in a stripe pattern and enclosed in a heat-shrinkable tube. When the colored solution was supplied to the detecting tube, blue zebra-bands formed, and the ammonium concentration was determined by counting the number of zebra-bands. The detection range was 1-20 mg-N l−1. Ammonium ion in actual domestic wastewater samples was successfully detected by means of this method.