An Electrochemical Gas Sensor Based on Paper Supported Room Temperature Ionic Liquids

A sensitive and fast-responding membrane-free amperometric sensor is described for the detection of electroactive species in gaseous atmospheres which exploits some profitable properties of room temperature ionic liquids (RTILs), such as their high electrical conductivity and negligible vapor pressure. It was assembled by screen printing working, reference and counter electrodes, by using carbon ink and a suitable mask, on one face of a filter paper foil which was then soaked with RTIL. Thanks to a careful control of the screen printing procedure and of the RTIL amount used for wicking paper, a so widespread contact between RTIL and electrode material could be achieved at the probe surface as to allow analytes to undergo charge transfer just as soon as they reach the three-phase sites where the electrode material, paper supported RTIL and the gas meet, thus avoiding the involvement of fairly slow steps such as analyte diffusion or dissolution in a conductive medium. The RTIL soaked paper electrochemical detector (RTIL-PED) adopted was prepared by using 1-butyl-3-methylimidazolium bis(trifluoromethansulfonyl)-imide ([BMIM][NTF2]), it being found the most suitable RTIL for this purpose, and printing the working electrode by using carbon ink to which cobalt(II)-phthalocyanine was added, so as to profit of its ability to mediate thiol oxidation through an electrocatalytic process. This device was tested as a wall-jet amperometric detector for the flow injection analysis of 1-butanethiol vapors present in the head space in equilibrium with aqueous solutions at controlled concentrations, by estimating a quite favorable performance (detection limit : 0.5 μM; dynamic range : 2-200 μM, both referred to solution concentrations; correlation coefficient : 0.998; repeatability : ±7% relative standard deviation; long-term stability : 9%).