Spectrophotometric determination of nitrogen dioxide in air

A sensitive spectrophotometric method for the determination of trace amounts of nitrogen dioxide, after fixing it as nitrite in alkaline sodium arsenite solution, is described. The reaction is based on the diazo-coupling of p-nitroaniline with chromotrophic acid in acetate medium (pH 6±0.5). The azo dye formed has its absorption maximum at 515 nm, with a molar absorptivity of 3.7×104 l mol-1 cm-1. Beer's law is obeyed over the range 0-20 μg of nitrite. The relative standard deviation is 2.5% for ten determinations of 10 μg of nitrite. The effect of interfering gases and ions on the determination is discussed. The method has been applied to the determination of residual nitrogen dioxide in a laboratory fume cupboard and the results are compared with those obtained by the widely used sulphanilamide - NEDA method. Down to 0.5 μg of nitrite can be determined. © 1993 Springer-Verlag.