Automated determination of ammonium in natural waters with reverse flow injection analysis based on the indophenol blue method with o-phenylphenol

Abstract

An automated colorimetric method for the determination of ammonium in natural water was established using an integrated reverse flow injection analysis (rFIA) system based on the indophenol blue method with o-phenylphenol, which is a less toxic phenolic compound. The system was operated with laboratory-programmed software written in LabVIEW. The experimental parameters for ammonium determination were optimized based on a univariate experimental design. With the optimized conditions, the detection limit of the proposed method was 0.07μmol·L−1 and 0.08μmol·L−1, and the linearity was up to 50μmol·L−1 and 35μmol·L−1 for fresh water and seawater, respectively. The relative standard deviations were below 1.3% (n=8) and the recoveries varied from 89.8±1.0% to 106.5±2.9% for spiked natural water samples. The sample throughput was about 30h−1. The salinity effect from seawater was carefully investigated. The system has been successfully applied in-field in the Jiulong River for 24h on-line monitoring of ammonium concentration in surface water, and also used in the laboratory for analysis of ammonium in estuarine and coastal water samples. The analytical results obtained with the proposed method shown good agreement with those using reference methods. All results indicated that the newly developed automated rFIA method for ammonium determination was well suitable for laboratory analysis as well as for on-line monitoring.