Ionic liquids - inherent sensing and transduction of metal ion complexation

Ionic Liquids (IL’s) - being organic salts that are liquid at room temperature, display inherent ionic conductivity and a wide electrochemical window. This has led to their inevitable incorporation into electrochemical sensing techniques1. Radio Frequency (RF) detection provides a technique which can monitor conductivity wirelessly, but also has the required sensitivity and is non-invasive on the sample. We have used the IL trihexyltetradecylphosphonium dicyanamide[P6,6,6,14][DCA] which can easily be incorporated and solidified into a polymeric membrane. The resulting clear, homogenous membrane shows an optical response upon co-ordination to the metal ions Cu2+(yellow)and Co2+ (blue), and both ions simultaneously (green). RF can not only discriminate between the coordinated and noncoordinated membranes, but also between the individual co-ordinated membranes. The resultant downward trend in conductivity has been validated by Electrochemical Impedance Spectroscopy (EIS) and by X-Ray Flourescence (XRF). XRF shows that the results obtained from RF and EIS are directly related to the binding selectivity of the ligand [DCA]-. IL’s can bind to a variety of heavy metal ions and other important target analytes such as CO2.2 If a drop in conductivity can be presumed upon binding to an analyte, then the inherent conductivity properties of IL’s could be exploited in future electrochemical sensing. 1 . D. Wei., Anal. Chim. Acta. 2008, 607, 126-135 2 . E. Bates., J. Am. Chem. Soc,2002