FILTRATION APPARATUS

This invention relates to filtration apparatus and more particularly to apparatus in which a fluid containing solids, such as a biological specimen, is forced by centrifugal action through a filter to separate the solids from the liquid.

The present invention seeks to improve the apparatus disclosed in U.S. Patent Specification No. 4832851. Reference is made to that Specification for a fuller understanding of the present invention.

Using the apparatus of U.S. Specification No. 4832851 a fluid specimen, such as a biological sample, is forced through a filter by the action of a centrifuge. The filtrate is poured off and then the filtered solids, the retentate, are cleared from the filter membrane. This operation is not easy to perform. It may require repeated centrifugal action to clear the retentate from the filter. This has meant that the apparatus as disclosed in U. S.

Specification No. 4832851 is not as commonly used as it might be.

The present invention offers a solution to this problem particularly, although not exclusively, when the solution to be filtered is of a highly viscous nature.

Another object of the present invention is to provide apparatus in which the filter membrane is protected against damage when the filtering vessel is not in the container.

In accordance with one aspect of the present invention there is provided filtration apparatus comprising a container having a closed end and an open end, a filtering vessel which is a sliding fit within the container and a filter medium bridging the open, lower end of the filtering vessel, characterised by the provision of a filler element on the side of the filter medium remote from the filtering vessel, the filler element substantially filling the volume of the container on the side of the filter medium remote from the filtering vessel when the latter is in a position closest to the closed end of the container. The filler element preferably has a bore in which retentate will accumulate when the apparatus is subjected to centrifugal force.

Means is preferably provided for displacing the filtering vessel relative to the container between a filtering position near to the closed end of the container and a position removed from the closed end of the container, in which latter position retentate on the filter and/or on or in the filler element can be dislodged into the closed end of the container by further centrifugal action. The apparatus may comprise a lid which closes the open end of the container, the filtering vessel having a neck portion which extends through an aperture in the lid, the neck portion having projections which cooperate with slots in the lid opening to the aperture to be displaceable between an operative position in which the projections are in the slots and a retracted position in which the projections are removed from the slots.

In accordance with another aspect of the present invention there is provided a method of using the apparatus described in the four immediately preceding paragraphs, the method comprising positioning the filtering vessel close to the closed end of the container whereby the filler element substantially fills the volume of the container on the side of the filter remote from the filtering vessel, pouring a solution to be filtered in to an outer chamber of the filtering vessel, subjecting the apparatus to centrifugal action whereby liquid of the solution is forced through a filter into an inner chamber of the filtering vessel and solids of the solution remain on the side of the filter remote from the filtering vessel, decanting the liquid from the filtering vessel, retracting the filtering vessel from the container so that a filler element on the side of the filter remote from the filtering vessel becomes spaced from the closed end of the container and subjecting the apparatus to a second centrifugal action whereby retentate on the filter and/or on or in the filler element is dislodged into the closed end of the container. Preferably the solution is highly viscous. A preferred embodiment of the invention will now be described by way of non-limitative example with reference to the accompanying drawing, in which:

Figure 1 is a sectional elevation of apparatus in accordance with the present invention. Referring now to the accompanying drawing, the apparatus 10 comprises a container 11 having a closed end 12 and an open end 13. Within the container 11 and slideable relative thereto is a filtering vessel 15 which has a central tube 14 from which fins 16 extend into contact with the inner wall of the container 11 to provide an outer compartment 23 of the filtering vessel. The fins 16 do not extend the full length of the tube 14 so that the filtering vessel can be reciprocated in the container 11.

The tube 14 has a neck portion 17 above the fins 16 which extends through a central aperture in a lid 18 which is screw-threaded onto the open end of the container 11. Tabs or ears 19 project from the neck portion 17 near to its upper end. The lid 18 is formed with slots (not shown) opening to its central aperture into which the tabs 19 can be inserted to bring the filtering vessel into a position in which filtering can be effected. Alternatively the filtering vessel can be partially withdrawn from the container 11 (to the position in which it is illustrated) and rotated until the tabs 19 are not aligned with the slots. Bridging the bottom end of the filtering vessel is a filter 20. Below this and helping to secure the filter in position is a filler element 21. This is shaped substantially to fill the volume of the container 11 on the side of the filter 20 remote from the filtering vessel 15 when the latter is in a lowered position in the container. The filler element 21 has a central bore 22.

In use of the apparatus 10 illustrated the filtering vessel 15 is rotated until the tabs 19 are aligned with the slots in the lid 18 and then pushed into the container 11 until the filler element substantially fills the volume of the container which is below the filter 20. The lid 18 is removed and a solution to be filtered is decanted into the outer compartment 23 of the filtering vessel. The apparatus 10 is positioned in a centrifuge (not shown) the action of which forces the liquid in the solution through the filter 20 and into the tube 14 of the filtering vessel, the solids (retentate) of the solution remaining on the side of the filter 20 remote from the filtering vessel and in the bore 22 of the filler element 21.

The apparatus 10 is taken away from the centrifuge and the lid 18 removed. Filtered liquid is decanted from the tube 14. The filtering vessel 15 is then pulled out of the container 11 and rotated until the tabs 19 are not aligned with slots in the lid 18. This is the position in which the apparatus 10 is illustrated in the drawing. It will be observed that there is now a gap between the filler element 21 and the closed end of the container 11. The apparatus 10 is then returned to the centrifuge and subjected to a second centrifugal action. This dislodges the retentate from the filter 20 and the bore 22 in the filler element into the closed end 12 of the container. The filtering vessel 15 can be removed from the container 11 and the retentate solids removed from the container 11.