Acknowledgement

1. Cu2+ Co2+ Cu2+/Co2+ Wireless Radio Frequency detection of Ionic Liquid simplified polymeric optodes Andrew Kavanagha, Matthius Hilderb, Noel Clarkb, Aleksandar Radua and Dermot Diamonda a CLARITY, The Centre for Sensor Web Technologies, National Centre for Senor Research, School of Chemical Sciences, Dublin City University, Dublin, Ireland. b CSIRO Materials Science and Engineering, Bayview Avenue, Clayton, Melbourne, Australia. Introduction: This study is based on two distinct research themes with many favourable aspects for use in Analytical Chemistry. Firstly, polymeric optodes are a well studied class of analytical sensors; whose response is generated upon transduction between the target analyte and a ligand. To date polymeric optodes sensors have been developed for most transition metal ions, as well as important analytes in clinical research. Equally, Ionic Liquids (IL’s) - a class of organic salts that are liquid at room temperature – have found an increased used in important areas such as in electrochemical analysis, as well as in chromatography and in liquid extractions. This worked is aimed at integrating IL’s into polymeric optodes, where they will be used to generate the sensor response. In this example the plasticizing abilities of the IL is used to generate transparent flexible poly(vinylchloride) PVC membranes. The optical response is obtained upon the formation of a charge-transfer complex between the anion and the heavy metal ions Cu2+ and Co2+. (b) (a) Fig 1: (a) The IL used in this study; trihexyltetradecylphosphonium dicyanamide (b) Response obtained for IL simplified polymeric optodes; yellow upon exposure to Cu2+ ions (left), a mixture of Cu2+ and Co2+ ions (green) and upon exposure to Co2+ ions (blue). Receiving Electrode (a) (b) Insulating Housing Material AC Transmitting Electrode Fig 3: (Top Left) The RF detection instrument used in CSIRO laboratories (Top Right) Response signals obtained via RF for IL based membranes (Bottom) Results obtained via peak area integration for membranes of differing component ratios The WRF detector system used in this study utilises radio frequency technology in order to obtain the conductivity of a sample as it passes through a defined point. This point is the transmitting electrode, which passes a low voltage, low-frequency AC signal toward a receiving electrode wirelessly. The sample to be analysed is housed in an insulating polystyrene based container which is placed on a miniature conveyor. Fig 3:(Top) EIS spectra obtained for (a) PVC:IL 1:2 and (b) PVC:IL 1:1 (Bottom) Resistance and conductivity values obtained from EIS spectra WRF detection is a novel technique producing peak heights of arbitrary units, and therefore its results must be validated appropriately. For this purpose, Electrochemical Impedance Spectroscopy (EIS) was employed, as this provides an independent estimation of the sample conductivity in S/cm. The resulting x-axis intercept of the Nyquist plot (fig 3.) is used to determine the resistance of charge transfer (RCT) of the membrane, which is then converted to the corresponding conductivity. Here the trend is inverted from the previous result obtained, which means that it is therefore an effective validation of the novel WRF instrumental result Conclusions: In this work have effectively shown how the results obtained from 3 differing techniques can be easily inter-related. In this case the IL based polymeric optodes are capable of discriminatory co-ordination of the heavy metals Cu2+, Co2+ and both ions in a mixture which produces an equal discriminatory conductivity decrease in the WRF signal. By documenting the inverse trend of impedance, we have validated this novel conductivity result. Both the WRF and EIS trends were then easily explained by studying the co-ordinating preferences of the IL ligand [DCA]-. This was achieved by quantifying the amount of metal present in the membrane using XRF. By combining the many advantageous properties of both IL’s and conductivity detection, then dramatic gains in sensing materials AND detection can be achieved. Fig 5:(Top) A typical XRF spectrum obtained for each individual membrane (Bottom) Concentration of each metal in membranes of differing component ratios X-ray fluorescence was then finally used to explain why a selective increase/decrease was seen in the results obtained previously. This selective response is a direct function of the binding nature of the IL. We have seen previously that whilst [P6, 6, 6, 14] [DCA] is capable of binding to both Co2+ and Cu2+, the preferentiality of the IL is toward Cu2+ . Acknowledgement This work is supported by Science Foundation Ireland under grant 07/CE/I1147 including the SFI-funded National Access Programme (NAP) grant NAP210 and by Enterprise Ireland grant 07/RFP/MASF812, which is part of EU-MATERA initiative.