A Submersible Battery-powered Flow Injection (FI) Sensor for the Determination of Nitrate in Estuarine and Coastal Waters

The design, construction and performance of a remotely deployed submersible flow injection-based nutrient (total oxidized nitrogen) sensor are described. The sensor featured a custom-built microcomputer and a solid-state, flow-through spectrophotometric detector, and the derivatization chemistry was based on in-line copper-cadmium reduction of nitrate to nitrite, and diazotization with N1NED and sulphanilamide. The limit of detection was 0.0014 mg l(-1) NO3-N and the linear range was 0.0014- 0.77 mg l(-1) with a 260 microl sample volume and a 20 mm path length flow cell. Results from submersed deployments in the Tamar estuary and North Sea are also reported.