On-line monitoring of phosphate in natural water and effluent streams using sequential injection analysis

Automation of the molybdenum blue method by sequential injection (SIA) for the on-line monitoring of phosphate in natural waters is presented. Although sequential injection analysis runs at one fifth the speed of conventional FIA, it presents many advantages such as simplicity of the manifold, robustness and computer compatibility. A reduction in reagent and sample consumption is also observed. Flow detector fouling does not occur in SIA manifolds as the detector is in contact with water between analysis. The proposed SIA analyser is able to monitor phosphate in the range 0–70 mg l−1 with a standard deviation of 0.9%. The detection limit is 0.5 mg l−1 PO43−.