Continuous-flow system for the accurate determination of low concentrations of ammonium ions using a gas-permeable poly(tetrafluoroethylene) tube decontaminator and an ammonia gas-sensing membrane electrode

Abstract

A continuous-flow system was designed for constructing a calibration graph for low concentrations of ammonium ions without risk of contamination. Standard solutions were prepared by diluting a limited volume of a standard ammonium chloride solution with a flow of ultra-pure water, from which residual ammonium ions had been previously removed as ammonia by passage through a gas-permeable poly(tetrafluorethylene) tube decontaminator at pH 12. The measurable concentration range was between 1 × 10^–7 and 5 × 10^–6 mol dm^–3 when an ammonia gas-sensing membrane electrode was used as the detector. The accuracy was within ±0.3%, and the precision was in the range 0.8–1.1% for five independent determinations of 3.0, 7.0 and 20 × 10^–7 mol dm^–3 ammonium chloride. This system was applied to the determination of low concentrations of ammonium ions in lake water samples.