Submersible, Osmotically Pumped Analyzer 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 seawater. Osmotic pumps driven by a NaCl gradient propel both sample and reagents through a miniature continuous flow manifold. The analyzer operates with sample and reagent flow rates of about 12 and 1 μL h -1 , respectively (≃8 and 0.7 mL month -1 ), shows a linear response from 0 to 20 μM nitrate with a detection limit of 0.1 μM, and has a 90% response time of approximately 30 min. The analyzer can automatically standardize itself by correcting for baseline and sensitivity 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