Investigation of transfer behavior of protonated pyridine at the liquid/liquid interface using dual micropipettes

In this work, the ion transfer at the dual micro-liquid/liquid interfaces formed at the orifice of a dual micropipette is reported. The goal is to use one channel (“generator”) to support a liquid/liquid interface where ions can be transferred from the inner phase (water) to the outer phase (1,2-dichloroethane, DCE), and another micropipette (“collector”) in vicinity to collect the ions from the outer phase back into the inner phase. Generation/collection voltammetry has been employed and pyridine is chosen as a model compound to study the dependence of collection efficiency upon applied potentials and pH of generator and collector, respectively. The applied potential of the generator has been found no obvious influence on collection efficiency (η). Collection efficiency decreases from maximum to zero as applied potential of collector increases, and the relationship between η and applied potential and pH is discussed. We also demonstrate that the dependence of collection efficiency upon collector pH is rather complicated due to different mechanisms involved at below, near, or above pKa of pyridine. For ionizable species, the maximum collection efficiency (ηmax) is not only dependent on the geometry of the pipette, but also pH of the system.