A Membrane Free Amperometric Gas Sensor Based on Room Temperature Ionic Liquids for the Selective Monitoring of NOx

A conveniently assembled, sensitive and fast-responding membrane free amperometric sensor is described for the detection of nitrogen oxides in gaseous atmospheres which exploits some profitable properties of room temperature ionic liquids (RTILs), such as high electrical conductivity, negligible vapor pressure and good thermal stability. It consists of three Pt wires piercing through a Teflon rod, whose exposed head is coated with a steadily adhesive thin RTIL film assuring the necessary electrical conductivity among the electrodes. The negligible vapor pressure of the immobilized RTIL layer makes possible to eliminate the need for the use of membranes, thus avoiding the involvement of a slow limiting step such as analyte permeation. Preliminary voltammetric tests performed at this sensor in gaseous atmospheres proved that the oxidation of NO 2 and NO occurs at very close potentials, thus allowing effective NO x determinations. Instead, other atmospheric components able to act as possible interfering species (CO, H 2S and SO 2) were found to undergo oxidation only at quite higher potentials. The performance of this device was assayed under flowing conditions on synthetic nitrogen atmospheres with controlled NO x contents, which was changed in a wide range (0.01-10 3ppm v/v). At room temperature, repeatable (±3.9%) and linearly dependent current signals were recorded, allowing a detection limit of 0.96ppb v/v to be inferred. At higher temperatures (100°C) a lower detection limit (0.55ppb v/v) could be instead estimated. The possibility of using this sensor for monitoring NO x in reduced pressure atmospheres was also assayed.