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.