Alkali metal ions transfer across a water/1,2-dichloroethane interface facilitated by a novel monoaza-B15C5 derivative

In this paper, a novel monoaza-B15C5 derivative, N-(2-tosylamino)-isopentyl-monoaza-15-crown-5 (L), is used as an ionophore to facilitate alkali metal cations transfer across a water/1,2-dichloroethane (W/DCE) interface. Well-defined voltammetric behaviors are observed at the polarized W/DCE interfaces supported at micro- and nano-pipets except Cs⁺. The diffusion coefficient of this ionophore in the DCE phase is calculated to be equal to (3.3±0.2)×10⁻⁶ cm² s⁻¹. The experimental results indicate that a 1:1 (metal:ionophore) complex is formed at the interface with a TIC/TID mechanism. The selectivity of this ionophore towards alkali ions follows the sequence Na⁺>Li⁺>K⁺>Rb⁺>Cs⁺. The logarithm of the association constants (log β₁^o) of the LiL⁺, NaL⁺, KL⁺ and RbL⁺ complexes in the DCE phase are calculated to be 10.6, 11.6, 9.0 and 7.1, respectively. The kinetic parameters are determined by steady-state voltammograms using nanopipets. The standard rate constants (k⁰) for Li⁺, Na⁺, K⁺ and Rb⁺ transfers facilitated by L are 0.54±0.05, 0.63±0.09, 0.51±0.04 and 0.46±0.06 cm s⁻¹, respectively. The pH values of aqueous solution have little effect on the electrochemical behaviors of these facilitated processes. The results predicate that this new type of ionophore might be useful to fabricate electrochemical sensor of sodium ion.