Flow injection system for on-line potentiometric monitoring of ammonia in freshwater streams

Abstract

A flow injection system based on potentiometric detection and designed for on-line monitoring of ammonia in freshwater streams is described. A specially constructed all-solid state tubular flow-through ammonium electrode was used in conjunction with a gas-diffusion chamber to enhance its selectivity. Construction of the electrode involved the in situ formation and direct casting of the sensing nonactin-poly(vinyl chloride) membrane on to a mouldable conducting filled polymer (epoxy resin loaded with graphite), which acted as an internal solid contact, without an inner solution. The electrode response under dynamic conditions both with and without the gas-diffusion chamber was evaluated. After optimisation of the flow system parameters, over 30 samples with a wide range of ammonia concentrations (2 × 10^–5–10^–2M) could be processed per hour with a detection limit of ca. 10^–6M. The performance of the monitoring system under on-line conditions in a water treatment plant is also described.