Spectrophotometric flow-through gas sensor for the determination of atmospheric nitrogen dioxide

A flow-through gas sensor has been developed which relies on membrane based analyte collection and trapping in a temporarily halted liquid absorber and in situ spectrophotometric detection of the reaction product formed in solution. Through a stop-and-go sequence of the absorber solution provision is made for real-time detection of the preconcentration taking place in the minute absorber solution and ready elution after signal evaluation. The determination of nitrogen dioxide at concentration levels relevant to measurement of urban atmospheres is used to demonstrate the principle and capabilities of an inherently universal applicable gas sensing device. The detection chemistry used in the present work is identical to that of common standard methods (i.e., reaction of NO2 with mixed reagent containing sulfanilamide and N-(1-naphthyl)-ethylene-diamine) so that the same selectivity arises. The working range covered in this study is 50–250 μg/m3 NO2 with a time resolution of few seconds. Lower concentrations are accessible when longer preconcentration times are used. Reasonable precision (typically < 5% R.S.D.) and good long-term stability is given which makes frequent calibration unnecessary.