Abstract: A device and method is disclosed for the identification, concentration and isolation of a chemical compound from a mixture of compounds on the basis of the binding affinity of the chemical compound to a macromolecule or complex thereof, that is, to a receptor. Both the compounds to be assayed, and the macromolecules to which the compounds may bind, are free in solution. The method comprises contacting a mixture of compounds in solution with a solution of macromolecules or complexes thereof in a device possessing an ultrafiltration membrane to retain the receptor and bound compound receptor complex; washing through the device non-bound compounds; and releasing a bolus of the bound compound which passes through the ultrafiltration membrane where it may be analyzed chemically and/or spectrally (e.g. mass spectrometry) and/or bioassayed. The device includes a barrier such as an ultrafiltration membrane separating a binding chamber and an effluent chamber.