SPECTROPHOTOMETRIC DETERMINATION OF NITROGEN-DIOXIDE IN AIR AND NITRITE IN WATER AND SOIL SAMPLES

A sensitive spectrophotometric method for the determination of nitrogen dioxide in air and nitrite in water and soil samples is described. Nitrogen dioxide in air is fixed as nitrite ion in alkaline sodium arsenite or in triethanolamine absorber solutions. The method is based on the diazo coupling reaction between p-nitro aniline and 1-hydroxy-2-naphthoic acid. The azo dye formed under aqueous condition has an absorption maximum at 585nm and obeys Beer's law over the range 0-25 mu g of nitrite. The colour system is stable for 72h. The relative standard deviation is 2.7% for ten determinations at 15 mu g of nitrite. The dye is extracted with 1:1 isoamyl alcohol-IBMK mixture and stabilisation with methanolic potassium hydroxide showed lambda(max) at 610nm. It obeys Beer's law over the range 0-4 mu g of nitrite. The colour system is stable for 40h in organic phase and the relative standard deviation is 2.5% for ten determinations at 3 mu g of nitrite. The molar absorptivity of the colour system is 3.68 x 10(4) Lmol(-1) cm(-1). The effect of interfering gases and other ions on the determination of nitrite is described. The developed method has been applied for the determination of residual nitrogen dioxide gas present in the laboratory fume cupboard and automobile exhaust gases. In addition, the method has been applied for the determination of nitrite and nitrate in samples like water, soil and radiator coolants.