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

Abstract

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 NO2 and NO occurs at very close potentials, thus allowing effective NOx determinations. Instead, other atmospheric components able to act as possible interfering species (CO, H2S and SO2) 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 NOx contents, which was changed in a wide range (0.01–103 ppm v/v). At room temperature, repeatable (±3.9 %) and linearly dependent current signals were recorded, allowing a detection limit of 0.96 ppb v/v to be inferred. At higher temperatures (100 °C) a lower detection limit (0.55 ppb v/v) could be instead estimated. The possibility of using this sensor for monitoring NOx in reduced pressure atmospheres was also assayed.

Room Temperature Ionic Liquids As Useful Overlayers for Estimating Food Quality from Their Odor Analysis by Quartz Crystal Microbalance Measurements

“…Thus, sensors designed to generate current responses and exploiting both gas permeable membranes 12,13 and membrane-free devices were developed, these last based on either solid polymer electrolytes (SPEs) [14][15][16] or room temperature ionic liquids (RTILs). [17][18][19][20][21][22][23] Unfortunately, these sensors provides responses for specific classes of VOCs alone, while flavors come out almost always from the contribution of different volatile species.…”

“…To achieve retention of volatile compounds, overlayers consisting of GC stationary phases displaying adsorption properties, 30 supramolecular compounds, 31 organic polymers, 32 biomolecules 33 or room temperature ionic liquids (RTILs) [17][18][19][20][21][22][23]28,29 have been employed. Among these, RTILs appear to be particularly attractive for their good thermal and electrical conductivity, negligible vapor pressure and ability to dissolve several compounds, thanks to their amphiphilic character which can be tuned by tailoring suitably their cations and anions.…”

“…Just these profitable properties have promoted their increasing use for several applications, such as organic synthesis, 34 chemical analysis, 35 GC separations 36 microextractions 37 and electrochemical gas sensing. [17][18][19][20][21][22][23][38][39][40] Moreover, they have been adopted as soft-coatings for QCM gas sensors planned for the detection of some organic volatile species at either room or high temperature. 29,41 In this paper we propose an array of QCM sensors filmed with different RTIL overlayers for the analysis of flavors with complex composition.…”

Current Fluctuation Measurements of Amperometric Gas Sensors Constructed with Three Different Technology Procedures

“…There exist several three-electrode topologies (planar [7,8,29] and bulk [2,3]). have The interface of a typical gas sensor at WE facilitates transport of gas molecules to the working electrode/electrolyte interface by simple diffusion or with an aid of a simple air pump [3].…”

“…This fact may cause several disadvantages: (i) there is a danger of leakage of acidic electrolyte, (ii) a considerable size of sensors make their integration into smart sensor systems inconvenient, (iii) sensor construction is not suitable for low-cost mass production techniques, (iv) problems arise from evaporation of the internal electrolyte [7]. As a remedy, solid polymer electrolyte (SPE) can be used [3,4,[7][8][9][10].…”