Characterization and reduction of interferences in flow-injection analysis for the in situ determination of nitrate and nitrite in sea water

The aim of this work is to improve the precision and the sensitivity of nitrite and nitrate determination by flow-injection analysis (FIA) for an in situ utilization. Two kinds of signal treatment are proposed in order to eliminate the refractive index provoked by the heterogeneous flow in FIA and the errors induced by temperature, salinity and pressure variations. The concentration range of this method is 0–100 μM NO−3-N with a detection limit (3σb) of 0.45 μM NO−3-N (At = 0.151CNO3 + 0.072, n = 40, r2 = 0.997). The relative standard deviation is 5% for nitrate solutions containing 0.5 μM NO−3-N. The sampling rate is about 45 h−1.