Apparatus and methods are disclosed for concentrating one or more components in a fluid effluent, which comprises fractions comprising separated components of interest. The fluid effluent is passed through a concentration device comprising a hollow element comprising a wall at least a portion of which is porous wherein the hollow element is disposed in the interior of a hollow liner. Fluid effluent molecules are permitted to permeate through the wall of the hollow element so that component molecules are concentrated in remaining effluent, which exits the concentration device. The component or components may then be detected.