Abstract: A reactor/separator device is provided for use in automated solid phase immunoassay. The device is a column, fitted at the bottom portion thereof with a water impermeable disc which can hold immunoabsorbents immobilized antisera, ion exchange resins and the like. When the contents of the column supported by the disc are brought into contact with an aqueous phase containing reagents or reactants by centrifugal force, a chemical reaction is initiated. After reaction, centrifugally applied pressure forces the aqueous phase through the filter disc making it water permeable and separating a desired component for subsequent analysis.