Analytical Sciences

Collection of Indonaphthol Blue on a Membrane Filter for the Spectrophotometric Determination of Ammonia with 1-Naphthol and Dichloroisocyanurate

Takashi SHOJI* and Eiko NAKAMURA**

*Department of Risk Management and Environmental Sciences, Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama, Kanagawa 240-8501, Japan
**Course of Environmental Science, Faculty of Education and Human Sciences, Yokohama National University, 79-2 Tokiwadai, Hodogaya, Yokohama, Kanagawa 240-8501, Japan

In order to determine ammonium ion in water samples, we propose a method based on the Berthelot reaction of ammonia with 1-naphthol and dichloroisocyanurate to form an indophenol blue derivative and collection of the blue compound as an ion pair using Zephiramine on a pure polytetrafluoroethylene (PTFE)-type membrane filter. The ion pair on the filter was eluted with 5.0 mL of acetonitrile, and the absorbance of the eluate was measured at 725 nm. The detection limit of the method was 2.5 μg L⁻¹ of ammonium ion. We showed that the interference of foreign ions was removed by the addition of EDTA. We also demonstrated the success of the method in determining ammonia in river water and seawater.

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