Abstract: A chamber for rotation about a rotational axis to separate blood components includes first and second spaced apart side walls forming a separation zone. Blood conveyed into the separation zone separates into a first region of cellular components, a second region of plasma, and an interface region between the first and second regions. An outlet conveys the second region of plasma from the separation zone. An interior wall extends into the separation zone to permit passage of the second region of plasma to the outlet while retarding passage of the interface region and the first region of cellular components to the outlet. The tapered second surface has a major axis that is oriented at a non-parallel angle with respect to the axis of the outlet. Due to this orientation, the boundary between the interface region and the other two regions is held uniform along the tapered surface.