Abstract: The invention relates to a device and process for separating selected fractions of liquids, preferably the fractions arising in density gradient centrifugation. Said device is characterized by a functional element, which is a space-enclosing element, its surface being partly formed by a net through which the free streaming of materials can occur in a liquid medium, the structure of the net ensuring that the liquid fraction entrapped in the space of the element is removable from the liquid medium by removing the element itself. For the purpose of density gradient centrifugation, a plurality of said functional elements are placed in a centrifuge tube, and after centrifugation, the specific fractions of the liquid entrapped in the inner spaces of the functional elements are separated by removing said functional elements one by one from the common housing tube.