METHOD AND APPARATUS FOR THE PROVISION OF FLUID INTERFACE BARRIERS

New and improved method and apparatus for the provision of a satisfactory physical and chemical barrier at a fluid interface in the nature of that which occurs at the interface of the separated plasma and packed cells layers in centrifuged blood samples are provided, and are embodied by barrier means which are of greater specific gravity than said blood plasma layer but lesser specific gravity than said blood cells layer and are operable, upon insertion into a centrifuged blood sample container, to sink through said blood plasma layer substantially to said interface and to be wetted and expanded by said blood plasma to expand into firm contact with each other and with the walls of said container to automatically form said barrier at said interface.