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 p hotometric monitor are described. The system is controlled by an in-ho use microcomputer system that enables the monitor (including a solid s tate detector) to operate from a 12-V battery supply. Two monitors hav e 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 ra nge of 0 to 2000 mu g L(.1) and a limit of detection of 70 mu g L(.1). Six river water samples were analysed by the monitors and the results obtained were in good agreement with standard spectrophotometric meth ods. The nitrate monitor was operated continuously for three weeks and produced good results for 82% of this period. The accuracy and precis ion of the nitrate system were examined over a 3-d period and both fou nd to be better than 2%.