Determination of trace amounts of ammonia in air using a batchwise collection/concentration method by spectrophotometry

Abstract

Ammonia in the atmosphere can be determined by an improved indophenol method with 1-naphthol. Ammonia dissolved in water reacts with sodium hypochlorite in the presence of sodium hydroxide and 1-naphthol to form an indophenol blue dye, which can be measured at 720 nm (maximum absorbance). Since ammonia in the atmosphere can be absorbed in purified water almost completely, a calibration graph using standard aqueous ammonium chloride solutions can be used. The calibration graph showed a good linearity (y = 0.37 × 10 5 x + 0.027, R 2 = 0.9992) and the detection limit was 0.9 × 10 -6 M. For practical samples, the air was collected into a 50 ml plastic syringe with an air-tight cap containing 3.0 ml of purified water as the absorbing solution, followed by shaking it by hand. The method was successfully applied to the determination of ammonia in indoor and outdoor air samples. © 2005 The Japan Society for Analytical Chemistry.