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 C_nMeImCl (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 C_nMeImCl 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 ($\Delta G_m^{\circ }$), degree of counterion dissociation (α), amphiphile tail transfer Gibbs free energy ($\Delta G_{m,\text{trans}}^{\circ }$) 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.