Potentiometric Response Characteristics of Membrane-BasedCs+-Selective Electrodes Containing Ionophore-Functionalized Polymeric Microspheres

Shane Peper,Chad Gonczy

doi:10.4061/2011/276896

Abstract

Cs+-selective solvent polymeric membrane-based ion-selective electrodes (ISEs) were developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) as the ion exchanger. A systematic study examining the effects of the membrane plasticizers bis(2-ethylhexyl) sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and 2-fluorophenyl nitrophenyl ether (FPNPE) on the potentiometric response and selectivity of the corresponding electrodes was performed. Under certain conditions, P-EG-based ion-selective electrodes (ISEs) containing TFPB and plasticized with NPOE exhibited a super-Nernstian response between1×10−3and1×10−4 M Cs+, a response characteristic not observed in analogous membranes plasticized with either DOS or FPNPE. Additionally, the performance of P-EG-based ISEs was compared to electrodes based on two mobile ionophores, a neutral lipophilic ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) and a charged metallacarborane ionophore, sodium bis(dicarbollyl)cobaltate(III) (CC). In general, P-EG-based electrodes plasticized with FPNPE yielded the best performance, with a linear range from 10-1–10-5 M Cs+, a conventional lower detection limit of8.1×10−6 M Cs+, and a response slope of 57.7 mV/decade. The pH response of P-EG ISEs containing TFPB was evaluated for membranes plasticized with either NPOE or FPNPE. In both cases, the electrodes remained stable throughout the pH range 3–12, with only slight proton interference observed below pH 3.

Highlights

As a regulated environmental contaminant at nuclear processing facilities and as a possible constituent in radiological dispersal devices, 137Cs is an important analyte for which early detection systems must be available
One wellestablished class of electrochemical sensors that is capable of meeting these criteria and that has been widely used for measuring inorganic ions, including alkali metals, is the solvent polymeric membrane-based ion-selective electrode (ISE) [1]
Membrane-based ISEs are composed of a plasticized poly(vinyl chloride) (PVC) matrix that is incorporated with an ionophore and an ion exchanger

Summary

Introduction

As a regulated environmental contaminant at nuclear processing facilities and as a possible constituent in radiological dispersal devices, 137Cs is an important analyte for which early detection systems must be available. ISE membranes contain mobile active sensing components (e.g., ionophore) Over time, these components slowly leach from the membrane, resulting in decreased sensor performance [2]. In addition to improving sensor longevity, ionophore immobilization has resulted in other apparent advantages, such as improved lower detection limits [13], and elimination of dimer formation within ion-selective membranes based on metalloporphyrins [14]. One approach for immobilizing ion-selective ligands that is becoming increasingly more popular for chromatographic separations, but has yet to be studied for its applicability in ISEs, is grafting the ionophore onto cross-linked polymeric microspheres [15,16,17]. In addition to ionophore immobilization, the chemical structure and polarity of the membrane plasticizer can have a dramatic effect on electrode performance (e.g., selectivity) [18]. P-EG-based electrodes are compared to both a new charged Cs+ ionophore, bis(dicarbollyl)cobaltate(III) (cobalticarborane, CC), and a lipophilic, mobile ethylene glycol derivative, ethylene glycol monooctadecyl ether (UEG)

Experimental

Results and Discussion

Conclusion