Spectrophotometric or coulometric determination of nitrate with an electrochemical reductor using flow injection

Abstract

A column electrode (CE) packed with co-electrodeposited Cu-Cd glassy carbon grains has been shown to be excellent for the reduction of nitrate to nitrite, and its application to the flow analysis of nitrate in samples of natural water has been studied. Controlled-potential flow electrolysis at a Cu-Cd deposited CE was used to reduce nitrate to nitrite at potentials from –0.85 to –1.05 V versus Ag-AgCl in pH 10 ammonia buffer solution; nitrite, however, was not reduced under similar conditions. Accordingly, nitrate could be determined indirectly by detecting the nitrite produced with a conventional colour reaction (detection limit, 7 × 10^–7M). In addition, by using an Ag deposited CE as an electrochemical oxygen scrubber prior to the Cu-Cd deposited CE it was possible to determine nitrate coulometrically without interference from the coexisting oxygen or nitrite (detection limit, 2 × 10^–6M). The preparation, regeneration and post-treatment of these metal-deposited CEs were very simple procedures, compared with the conventional Cu-Cd column, and this system should be well suited for automatic measurements of nitrate.