An automated spectrophotometric field monitor for water quality parameters : Determination of nitrate

An automated spectrophotometric field monitor is described for the determination of nitrate in river water. The bias, precision and linear calibration range of the monitor were determined in the laboratory. Samples taken from six locations on the River Frome in Dorset were analyzed for nitrate content by the monitor, and the results obtained were in good agreement with those obtained by two spectrophotometric reference methods. The relative standard deviation for 672 replicate injections of a 7.7 mg l^?1 NO₃ standard over a 14-day period was 1.4%, during which time 2.51 of the colour reagent and 2.5 1 of the ammonium chloride solution were consumed. The linear calibration range of the procedure was 0–12 mg l^?1 NO₃-N. Results are also presented for a four-day field trial on the River Frome.