A dynamic acetonitrile | aqueous electrolyte phase boundary in contact with platinised Teflon working electrodes is investigated. High concentrations of salt in the aqueous phase (2 M NaCl and 0.1 M NaClO4) ensure immiscibility and the polar nature of acetonitrile aids the formation of a well-behaved triple phase boundary reaction zone. The one-electron oxidation of tert-butylferrocene in the organic phase without intentionally added electrolyte is studied. The limiting current for the flowing triple phase boundary process is shown to be essentially volume flow rate independent. The process is accompanied by the transfer of perchlorate from the aqueous into the organic phase and the flux of anions is shown to be approximately constant along the dynamic acetonitrile | aqueous electrolyte | platinum line interface. A high rate of conversion (close to 100%) is achieved at slow volume flow rates and at longer platinum electrodes.