Rapid and coulometric electrolysis for ion transfer at the aqueous|organic solution interface

Abstract

A flow cell was developed for the rapid and coulometric ion transfer at the aqueous|organic solution (W|O) interface to which a potential difference, E, was applied. The cell was composed of a porous Teflon tube (1.0 mm in inner diameter), a silver wire (0.8 mm in diameter) inserted into the tube, a platinum wire placed outside the tube, O into which the tube was immersed and a reference electrode, RE, in O. The W containing a species of interest was flowed through the narrow gap between the tube and the silver wire. The E was applied by using the silver wire and RE, and the current due to the interfacial ion transfer was detected by the silver and platinum wires. The developed cell was evaluated adopting the transfer of K + from W to 1,2-dichloroethane facilitated by dibenzo-18-crown-6. The ion transfer with efficiency more than 99% was attained when the tube was longer than 50 cm and the flow rate of W was slower than 0.2 ml min −1, which means the quantitative ion transfer is completed within 40 s. The coulometric determination of 2 × 10 −4 to 2 × 10 −3 mol dm −3 K + could be attained with an accuracy of 100 ± 1% ( n = 5) by the electrolysis for 30 min. The accuracy and precision for 5 × 10 −4 mol dm −3 K + was 99.7 ± 0.1%. The coulometric determination of Mg 2+ or Ca 2+, and the feasibility of the cell as detectors in flow analyses were also examined.