Interfering Ions and Controlling Their Effects on the Direct Analysis of Total Dissolved Ammonia Nitrogen in Aquacultural Wastewater Using Molecular Absorption Spectrophotometry

Abstract

Various parameters related to water quality have to be concerned in the aquacultural water. Because of its potential toxicity, ammonia nitrogen is considered one of the most critical factors directly affecting aqueous organisms. The present study aimed to assess the impact of common ions, including Cl–, NO3–, NO2–, Ca2+, Mg2+, Fe3+, and Cu2+ on the Berthelot method (i.e., using salicylate and phenol reactions, which would be later mentioned as the salicylate method and indophenol method, respectively) for direct analysis of total dissolved ammonia nitrogen; and to find solutions to control these interfering ions. The results indicated that all investigated cations and Cl– were considerable effects on the determined ammonia concentrations; and the salicylate method was more advantageous than indophenol one with LOD and LOQ of 0.044 and 0.147 (mg L–1), respectively, a linear range of 0.05 to 1.00 mg L–1 NH3–N. Citrate was evaluated to be more efficient than EDTA for eliminating the influences of alkaline earth and transitional cations. The salicylate reagent was applied to determine the dissolved ammonia concentrations in the shrimp farming wastewater collected in the fringing of Can Gio mangrove (Ho Chi Minh City), with recoveries of 91.1-111%. The samples presented ammonia nitrogen levels ranging from 0.196 to 1.219 mg L–1, pH (7.27-7.72), salinity (7.9-24.1%), TOCs (0.165-1.633%), Mg (312-996 mg L–1), Ca (132-368 mg L–1), Fe (0.150-0.830 mg L–1), which met the Vietnam National Technical Regulation. The salicylate method could be a favorable, simple, reduced analysis time, saved costs, and especially environmentally friendly method that employed the UV-Vis spectrophotometry for direct determination of total ammonia nitrogen in aquacultural wastewater without any matrix removal steps.