Continuous ion species removal device and method

A method for treating a liquid sample stream, including a first analyte species ion and matrix ion species of opposite charge to said first analyte ion species, and for detecting said first analyte in the liquid sample stream, said method comprising flowing said sample stream from an inlet in a flow-through treatment channel to a sample stream outlet thereof, flowing a carrier liquid stream including a matrix ion species capture material through said flow-through channel to a carrier stream outlet thereof for removing said matrix ion species away from said first analyte ion species, said sample stream and carrier liquid stream flowing substantially parallel to each other in said treatment channel and forming a liquid interface between them, said matrix ion species in said sample stream diffusing through said interface to contact and become bound by said capture material in said carrier liquid by forming a salt or complex or by ion exchange so that the concentration of said matrix ion species at said outlet is at a substantially lower concentration than at said inlet, transporting the sample stream, but not the carrier stream, from said sample stream outlet, in a fluid conduit to a detector, and detecting said first analyte ion species in said sample stream by said detector.