An apparatus for detecting analytes in a liquid sample may include an elongated primary channel through which an ionic species flows, the primary channel extending through a primary channel member, a first regenerant channel through which a regenerant flows, the first regenerant channel extending adjacent to the primary channel and being formed in a first block, a first charged barrier having exchangeable ions capable of passing ions of only one charge, positive or negative, and of blocking bulk liquid flow, the first charged barrier disposed between the primary channel member and the first block for separating the primary channel from the first regenerant channel, and a first sealing member disposed between the first charged barrier and the first block defining the first regenerant channel.