Abstract: A method is provided for changing a property of a sample. A sample, comprising particles suspended within a sample fluid, is introduced into a channel which comprises two walls that are permeable to a flow of fluid. A cross-flow is introduced at a predetermined temperature and of a predetermined chemical composition into the channel through a wall. This cross-flow flows at a first velocity and exits in a first direction through the other wall. An imposed field is applied on the particles in a second direction counter to the first direction of the cross-flow. The imposed field causes the particles to migrate at a second velocity opposite and/or equal to the first velocity of the cross-flow. Particles that are approximately balanced by the first and second velocities travel through the channel and are discharged in a fluid of predetermined chemical composition and at the predetermined temperature of the cross-flow.

Abstract: A radial opposed migration classifier is provided for separating particles in a sample, introducing and removing the particles into and out of the classifier at the same potential. A sample passes through a classification channel having two circular walls. The sample is introduced and exits the classifier through the same plane as the first wall, which is at a different potential from the second wall. A cross-flow fluid enters the classification channel through one of the walls. The cross-flow fluid flows at a first velocity and exits in a first direction through the other wall. An imposed field is applied on the particles in a second direction counter to the first direction of the cross-flow. This causes the particles of a desired size and/or charge to migrate at a second velocity opposite and/or equal to a first velocity of the cross-flow. The particles that travel through the channel are discharged.