SUBMERSIBLE, OSMOTICALLY PUMPED ANALYZERS FOR CONTINUOUS DETERMINATION OF NITRATE IN-SITU

A continuous flow analyzer powered by osmotic pumps has been developed to monitor nitrate concentrations while submerged in freshwater or se awater. Osmotic pumps driven by a NaCl gradient propel both sample and reagents through a miniature continuous flow manifold. The analyzer o perates with sample and reagent flow rates of about 12 and 1 mu L h(-1 ), respectively (approximate to 8 and 0.7 mL month(-1)), shows a linea r response from 0 to 20 mu M nitrate with a detection limit of 0.1 mu M, and has a 90% response time of approximately 30 min. The analyzer c an automatically standardize itself by correcting for baseline and sen sitivity drift by periodically injecting and analyzing known standard solutions. The system has operated continuously for month-long periods in freshwater and seawater and can be easily adapted to a variety of colorimetric analyses. Potential applications for this analyzer includ e environmental and oceanographic monitoring and process control.