The design and performance of a portable, automated flow injection monitor for the in-situ analysis of nutrients in natural waters

The design and performance of a battery-powered flow injection-based photometric monitor are described. The system is controlled by an in-house microcomputer system that enables the monitor (including a solid state detector) to operate from a 12-V battery supply. Two monitors have been developed: one for nitrate, the second for orthophosphate. The nitrate monitor has a linear range of 0 to 12 mg L −1 and a limit of detection of 0.05 mg L −1. The orthophosphate monitor has a linear range of 0 to 2000 μg L −1 and a limit of detection of 70 μg L −1. Six river water samples were analysed by the monitors and the results obtained were in good agreement with standard spectrophotometric methods. The nitrate monitor was operated continuously for three weeks and produced good results for 82% of this period. The accuracy and precision of the nitrate system were examined over a 3-d period and both found to be better than 2%.