Ionophores for Reference Electrodes Based on Organic Electrolytes

Reference electrodes (REs) based on moderately lipophilic electrolytes form an attractive principle for miniaturized, maintenance-free sensing systems. Unfortunately, their broader adoption has been hampered by shortcomings related to limited lifetime and sample contamination from electrolyte leaching as well as poor compatibility with complex sample matrices. While exploring highly lipophilic electrolytes offers a potential solution, the performance of the corresponding REs is compromised by a mismatched stoichiometric composition of the used salt. To address this, we describe here a novel potential stabilization mechanism that capitalizes on the presence of an ion mismatch in the reference electrolyte by incorporating an ionophore into the membrane. In contrast to conventional applications, combining ionophores with mismatched organic electrolytes generates a sample-independent interfacial potential through a combination of complexation and ion-exchange processes at the membrane/sample interface. The mechanism is investigated in more detail through theoretical simulations, and the approach is validated experimentally using commercially available lipophilic salts and potassium-selective valinomycin as the ionophore. While the resulting REs require further optimization for practical use, they already exhibit notable stability in KCl solutions, with response slopes as low as 0.4 ± 0.2 mV and only 2.7 mV variation across repeat calibrations over a wide concentration range.