A portable flow-injection instrument incorporating a miniature spectrometer for the real-time monitoring of nitrate in rivers

Abstract

A field-deployable, flow-injection-based instrument for monitoring nitrate in rivers is described. It incorporates a miniature spectrometer that gives full spectral acquisition (200–700 nm) in real time. This allows the dynamic range to be adjusted in the field to meet local requirements by monitoring at different wavelengths. For pristine environments, a linear range of 0–1 mg L⁻¹ NO₃-N (r² = 0.9998, n = 6) and a detection limit of 0.007 mg L¹ NO₃-N (based on blank plus 3s) were achieved by monitoring at 597 nm. For impacted environments, a linear range of 0–9 mg L⁻¹ NO₃-N (r² = 0.9998, n = 6) was achieved at 510 nm. Conventional peristaltic pumps were replaced by solenoid-operated, self-priming micropumps, and injection of sample was achieved by a series of electronic switching valves. The pulsations of the micropumps were effectively removed by subtracting the response at a nonabsorbing wavelength (444 nm). Instrument control and data acquisition and processing were done within a graphical programming environment. The monitor was successfully deployed for 3 days at the River Frome in Dorset, United Kingdom. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:183–193, 2000