A voltammetric ion-selective electrode based on the facilitated transfer of Li + by dibenzyl-14-crown-4 at the o-nitrophenyl phenyl ether/water interface was applied to the amperometric detector in a FIA system for Li + with a cation-exchange column. The current response was stably detected by pulse amperometry in which voltage pulses of short duration (50 ms) were applied at the interval of 2 s. With this FIA system, 0.2-2.0 mM Li + in aqueous solution could be determined even in the presence of 120-160 mM Na + , the detection limit being 0.15 mM. A test using artificial serum demonstrated the practical applicability of this system.

For 13 dipeptides with un-ionizable amino acid side chains, their transfer at the nitrobenzene/water interface facilitated by dibenzo-18-crown-6 (DB18C6) has been studied by ion transfer voltammetry. On the condition that the pH of the water phase is adequately low compared with the (\3.0È3.3) of the dipeptide, its pK 1 protonated form transfers across the interface as a univalent cation. The reversible half-wave potential determined at pH 2.3 by cyclic voltammetry has been found to show good correlations with the hydrophobicities of the dipeptides estimated by some previously proposed hydrophobicity scales of amino acid residues. Especially, an excellent correlation with R \ 0.991 has been obtained for the "" e †ective ÏÏ hydrophobicity scale proposed by Akamatsu and Fujita (J. Pharm. Sci., 1992, 81, 164), in which the steric e †ect of amino acid side chains seems to be correctly incorporated.

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A novel microflow cell with a nitrobenzene (NB)/water (W) interface was developed. A poly(tetrafluoroethylene) membrane filter was employed to prepare the NB/W interface which was formed over a thin channel (0.1 mm thick, 48 cm long) on a silver plate. The silver plate was electrolyzed in advance and served as an Ag/AgCl electrode for controlling the Galvani potential difference across the NB/W interface as well as detecting the current flowing through the interface. Using the microflow cell, complete electrolysis was accomplished for the interfacial transfer of a representative ion (i.e., tetramethylammonium ion). Thus, the present microflow cell was shown to be promising for coulometric (i.e., absolute quantitative) analysis of ions. Also, the microflow cell was shown to be useful for determination of the number of electrons for complicated charge-transfer processes at the oil/water interface.