Simple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic Liquid

Abstract

Novel solid contact iodide selective electrodes based on covalently attached 1,2,3 triazole ionic liquid (IL) were prepared and investigated in this study. Triazole-based IL moieties were synthesized using click chemistry and were further copolymerized with lauryl methacrylate via a simple one step free radical polymerization to produce a "self-plasticized" copolymer. The mechanical properties of the copolymer are suitable for the fabrication of plasticizer-free ion-selective membrane electrodes. We demonstrate that covalently attached IL moieties provide adequate functionality to the ion selective membrane thus achieving a very simple, one component sensing membrane. We also demonstrate the presence of iodide as the counter-ion in the triazole moiety has direct influence on membrane's functionality. Potentiometric experiments revealed that each electrode displays high selectivity towards iodide anions over a number of inorganic anions. Moreover the inherent presence of the iodide in the membrane reduces the need for conditioning. The non-conditioned electrodes show strikingly similar response characteristics compared to the conditioned ones. The electrodes exhibited a near Nernstian behavior with a slope of -56.1 mV per decade across large concentration range with lower detection limits found at approximately 6.3x10 -8 M or 8 ppb . These all-solid state sensors were utilized for the selective potentiometric determination of iodide ions in artificial urine samples in the nanomolar concentration range.Potentiometric chemical sensors, with primary responses based on extraction and molecular recognition processes are a wellstudied and understood class of sensing devices. 1 Ion selective electrodes (ISEs) have been already widely used in a variety of fields such as clinical analysis, 2 process control 3 and environmental monitoring. 4 Ion selective membranes are typically composed of plasticized polymers, ion exchange salts, and one or more ionophores. Each constituent plays a specific role in the proper functioning of these membrane based ISEs. 5 Spontaneous and non-specific extraction of analyte ions from the sample into the membrane bulk is primarily suppressed due to the highly hydrophobic nature of the polymer backbone. Ideally, polymer matrix should provide a homogenous medium in which all active components can move freely. This strongly resembles the composition of liquid membrane electrodes since their sensing components were simply dissolved in an organic medium. However, the performance of polymer-based membranes can be drastically reduced if such sensors are used for the measurements of ions within more lipophilic environments in biological samples including undiluted whole blood. The cross contamination of chemical sensors coupled with leaching of the sensing components from the ion selective membrane into the sample fundamentally limited the applications of ISEs as a robust analytical tool for long-term trace level analysis. 6 Over the years, a number of approaches have been developed to minim...

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