Cheap and effective potentiometric PVC sensor for the determination of imidazolium based ionic liquids in aqueous and aqua-organic media

Abstract

Owing to the extensive research on imidazolium based ionic liquids; the present study aims to design a potentiometric sensor for alkyl methylimidazolium ion. For this, poly(vinyl chloride) PVC membrane based on the neutral ion-pair complexes of cetylpyridinium chloride and sodium dodecyl sulfate (CPy+DS−) has been developed. The synthesized ion selective electrode (ISEs) have been found to show linear response with near-Nernstian slope for CnMeImCl (C10MeImCl, C12MeImCl and C14MeImCl). The proposed ISEs show quick response (5–6 s) and provide wide pH range for working. The influence of various ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined by separate solution method. The performance of synthesized ISE in examining the critical micellar concentration (cmc) of CnMeImCl in aqueous, aqua-organic media and in the presence of amino acids (glycine, L-glutamic acid and L-phenylalanine) has been found to be satisfactory and confirmed through conductivity and fluorescence measurements. This emphasizes its worth for in-situ analysis of alkyl methylimidazolium ions, during an organic reaction, and hence possible reaction mechanism evaluation. Different thermodynamic parameters such as Standard Gibbs energies of micellization (ΔGm∘), degree of counterion dissociation (α), amphiphile tail transfer Gibbs free energy (ΔGm,trans∘) have been evaluated. Further, the analytical application of synthesized electrode as end point indicator in the potentiometric titration of C14MeImCl with SDS has also been explored, which compared well with improved two-phase titration method. The current study is novel as it involves the use of a cheaper material (CPyCl) as ionophore and that the same electrode can be used for different chain alkyl methylimidazolium ions simply by changing the internal reference solutions.