A centrifuge separation device is disclosed and includes a rotor configured to be connected to a centrifuge motor for rotation about an axis of rotation. A retainer is associated with the rotor and defines a passageway for a separation channel. A protrusion formed in one of the passageway walls extends towards and is spaced from the other of the passageway walls. The protrusion is sized to substantially block passage of materials in a predetermined density range and to substantially permit passage of materials outside of the predetermined density range. An indentation formed adjacent the protrusion in a wall of the passageway opposite the protrusion is configured to trap fluid during rotation of the rotor and to cooperate with the trapped fluid to maintain a substantially Coriolis-free pathway in a region of the passageway adjacent the protrusion.