Extractive spectrophotometric determination of trace amounts of nitrogen dioxide, nitrite, and nitrate

A sensitive extractive spectrophotometric method for the determination of nitrogen dioxide in air and nitrite and nitrate in water, soil and blood serum is described. Nitrogen dioxide in air is fixed as nitrite in a suitable trapping solution. The method is based on the diazo coupling reaction between p-nitroaniline and N-(1-naphthyl)ethylenediamine dihydrochloride [NEDA]. The azo dye formed under aqueous conditions is extracted with isobutyl methyl ketone [IBMK]. The system obeys Beer's law over the range 0-3 mu g of nitrite at 545 nm and the colour is stable for 3 h. The molar absorptivity of the colour system is 5.7 x 10(4) L mol(-1) cm(-1). The relative standard deviation is 1.3% for ten determinations at 2 mu g of nitrite. Nitrate is determined as nitrite after reduction on a cadmium column. Negative interferences from SO2, H2S, Cu2+ and Cr3+ and positive interference from Fe2+ and Fe3+ can be simply masked.