Abstract: A free solution electrophones-membrane filter trapping assay apparatus includes a container and at least one porous membrane. The porous membrane and container define a chamber capable of holding run solution. A specimen containing particles to be classified is juxtaposed with the run solution. A voltage is placed across the specimen, run solution and membrane to cause particles to be released from the specimen. Particles enter the run solution and readily pass therethrough. Particles that are smaller in size than the pores of the membrane pass through the membrane while particles having a larger particle size do not. A method of classifying particles includes the steps of providing a sample of particles and a porous membrane, positioning a run solution between the sample and the membrane and applying an initial voltage across the sample, run solution and membrane.