The transfer of K+ facilitated by dibenzo-18-crown-6 was examined voltammetrically at an interface between water containing La3+, Eu3+ or Yb3+ and 1,2-dichloroethane (DCE) containing distearoyl L-alpha-phosphatidylcholine (DSPC). The reversible wave for the transfer of K+ from water to DCE vanished owing to the formation of a compact layer at the interface, which was caused by the complex formation of lanthanide ion with a DSPC monolayer. The blocking effect was enhanced in the order of La3+ < Eu3+ < Yb3+. The complex formation constants were evaluated approximately based on the decrease of voltammetric current. The inhibition of the reversible wave was accompanied by the appearance of a new voltammetric peak at more positive potentials for the restoration of K+ transfer corresponding to the destruction of the compact layer. The peak potential of the new wave shifts positively with an increase of pH and the concentration of lanthanide ion. The blocking effect on transfers of tetraethylammonium ion, bis(tributylammonium)propane ion, ClO4- or 1,5-naphthalenedisulfonate ion was also examined. (C) 2004 Elsevier B.V. All rights reserved.