An electrolytic device (8) includes four channels (10, 12, 14, 16) separated by three charged ion exchange barriers of the same type (18, 20, 22). The device can be used to suppress an eluent stream containing separated sample analyte ions and simultaneously pretreat a sample stream containing unseparated analyte ions by removing the counterions to the analyte ions under application of a single voltage. The device can also be used to suppress an eluent stream and convert the separated sample analyte ions to their acid or base form and then subsequently to their salt form.