A new, flat-angle centrifuge head system has been designed to fit a conventional table-top centrifuge. The rotor accommodates two major units: one for membrane filtration of human serum in the 20-1,000 micro-liter range and another for elution of human whole blood or urinary amino acids from filter paper discs. The samples can be processed in less than 15 minutes with the use of disposable accessories. The protein-free ultrafiltrates or the eluates from filter paper discs can be used for chromatography of amino acids.