Selective electrodes for [PF6]− and [BF4]− anions based on the associates formed by ionic liquid and cationic dyes

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C4mim][PF6] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF6]− compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF6]− sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF6]− are 59.7 ± 0.5 and 58.1 ± 0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0 × 10− 5–1.0 × 10− 1 or 1.0 × 10− 6–1.0 × 10− 1 mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3 ± 0.5 and 56.0 ± 0.5 mV/decade) for tetrafluoroborate anion [BF4]− in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF6]− and [BF4]− in aqueous ionic liquids samples and the solubility of the [PF6]− and [BF4]− based ionic liquids in water. The satisfactory results are obtained.

► Construction and performance of [PF6]− and [BF4]− selective electrodes are described.
► Ionic associates formed by ionic liquid [C4mim][PF6] and cationic dyes as ionophores.
► The sensors have good selectivity, wide working range, fast response time and reasonable lifetime.
► The electrode can be used in determining [PF6]− and [BF4]− in aqueous ionic liquids samples.