Ionic liquid salt bridge with low solubility of water and stable liquid junction potential based on a mixture of a potential-determining salt and a highly hydrophobic ionic liquid

A new type of ionic liquid salt bridge(ILSB) based on a mixture of pentyltripropylammonium bis(pentafluoroethanesulfonyl)amide, [N ₃₃₃₅ ⁺][C ₂C ₂N ^-], and heptadecafluorodecyltrioctylphosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate, [TOPH ⁺][TFPB ^-], shows a stable phase-boundary potential (δ _IL ^Wφ) between the ILSB and an aqueous solution of MCl (M = H ⁺, Li ⁺, Na ⁺, and K ⁺) over the concentration range from 0.05 mM to 0.5 M with an averaged excursion in 1 h of ±0.3 mV. The reproducibility of δ _IL ^Wφ is ±0.6 mV on average (95% confidence interval) in KCl solutions in this concentration range. The mixing of the two different types of salts not only increases the stability of the phase-boundary potential but provides us with more freedom in selecting potential-determining salts to design and customize ILSBs for different purposes.