Spectrophotometric determination of nitrate ion using nitrosation/FIA.

Abstract

N, N-Bis (2-hydroxypropyl) aniline (BHPA) reacts with nitrite ion in an acidic medium to form a red product, which has the maximum absorption at 500 nm. On the basis of this color reaction, FIA of nitrate was established. Nitrate ion could be reduced to nitrite ion by passing through the reduction column(2 mm×30 cm) packed with copperized cadmium {Cu(Cd) : particle size, about 0.5 mm}, which was installed just behind the sample injection valve. The carrier solution(10-3 M EDTA, pH 8) and the reagent solution (8×10-4 M BHPA, 0.35 M HCl, 0.15 M H3PO4) were propelled at the flow rate of 0.7 ml/min by using a double-plunger pump. The sample(120 μl) was injected into the carrier stream by using a 6-way injection valve. The reaction coil(0.5 mm×2 m) was kept in a thermostatically controlled water bath(80 °C). The cooling coil(0.5 mm × 50 cm), which was installed just behind the reaction coil, was kept in a water bath (tap water temperature). A calibration curve was linear up to 2×10-4 M nitrate. The detection limit corresponding to S/N=2 was 10-6 M nitrate, and the relative standard deviation (10 injections) was 0.4%, and the sampling rate was 40 samples per hour. Nitrate in river water at concentrations of 10-5 M level was determined.