Analytical Sciences

Sensitivity Improvement of Ammonia Determination Based on Flow-Injection Indophenol Spectrophotometry with Manganese(II) Ion as a Catalyst and Analysis of Exhaust Gas of Thermal Power Plant

Tomonori TSUBOI,*  Yoshio HIRANO,* Yoshinori SHIBATA,** and Shoji MOTOMIZU***

*The Chugoku Electric Power Co., Inc. Technical Research Center, 3-9-1, Kagamiyama, Higashi-Hiroshima 739-0046, Japan
**Chuden Kankyo Technos Co., Ltd., 3-9-1, Kagamiyama, Higashi-Hiroshima 739-0046, Japan
***Department of Chemistry, Faculty of Science, Okayama University, 3-1-1, Tsushima-naka, Okayama 700-8530, Japan

The sensitivity improvement of a flow-injection spectrophotometric method for the determination of ammonia was examined based on an indophenol blue coloration reaction with salicylate and hypochlorite in the presence of manganese(II) as a reaction promotion catalyst. The optimal conditions for achieving higher sensitivity of ammonia determination were examined using a three-line flow system. The limit of detection corresponding to a signal-to-noise ratio (S/N) of 3 was 0.005 mg l^-1 (≡5 ppb) of NH₄⁺. A calibration graph was linear in the range from 5 ppb to 1000 ppb of ammonium ion. The relative standard deviations (n = 9) for 50 ppb and 100 ppb of ammonium ion were 6.4% and 2.2%, respectively. The proposed method was applied to the determination of ammonia in the exhaust gas of a thermal power plant. Prior to the FIA determination, ammonia in the exhaust gas was absorbed into a boric acid solution; the absorption solution was then analyzed by the proposed FIA.

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