Real-time underway measurement of ammonium in coastal and estuarine waters using an automated flow analyzer with hollow fiber membrane contactor

Peng Li; Songtao Li; Dongxing Yuan; Kunde Lin

doi:10.1016/j.scitotenv.2023.163281

Real-time underway measurement of ammonium in coastal and estuarine waters using an automated flow analyzer with hollow fiber membrane contactor

Sci Total Environ. 2023 Jul 1:880:163281. doi: 10.1016/j.scitotenv.2023.163281. Epub 2023 Apr 5.

Authors

Peng Li¹, Songtao Li¹, Dongxing Yuan¹, Kunde Lin²

Affiliations

¹ Fujian Provincial Key Laboratory for Coast Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China.
² Fujian Provincial Key Laboratory for Coast Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China. Electronic address: link@xmu.edu.cn.

PMID: 37023803
DOI: 10.1016/j.scitotenv.2023.163281

Abstract

Ammonium (NH₄⁺) is an important parameter for aquatic ecosystems. To date, continuous and underway acquisition of NH₄⁺ in coastal and estuarine waters has been challenged by the strongly varying salinity and complex matrices in these waters. To address these issues, a hollow fiber membrane contactor (HFMC) was constructed and incorporated in flow injection analysis (FIA) to achieve online separation/preconcentration of NH₄⁺ in water. In the FIA-HFMC system, NH₄⁺ in the water sample was converted into NH₃ under alkaline conditions in the donor channel. The generated NH₃ diffused across the membrane and was absorbed in an acid solution in the acceptor channel. The resultant NH₄⁺ in the acceptor was then quantified based on a modified indophenol blue (IPB) method. Parameters affecting the performance of the FIA-HFMC-IPB system were evaluated and optimized. Under the optimized conditions, the proposed system exhibited a limit of detection of 0.11 μmol L^-1, with relative standard deviations of 1.0-1.9 % (n = 7), and a good linear response (R² = 0.9989) for the calibration in the field with NH₄⁺ standards in the range of 0.40-80 μmol L^-1. The proposed system was applied to a shipboard underway measurement of NH₄⁺ in a two-day cruise in the Jiulong River Estuary-Xiamen Bay, China. A good agreement was observed between measurements from the proposed system and those from manual sampling and laboratory analysis. Both laboratory and field results demonstrated that the system was free of salinity effect and interference from organic nitrogen compounds. The system also showed excellent stability and reliability during a 16-day observation. This work suggests that the proposed FIA-HFMC-IPB system is applicable for the underway measurement of NH₄⁺ in water, especially for estuarine and coastal waters with varying salinity and complex matrices.

Keywords: Ammonium; Flow injection analysis; Hollow fiber membrane contactor; Indophenol blue; Shipboard underway measurement.