Method and apparatus for filtering a liquid sample
The invention relates to the filtering of liquid samples, preferably in a laboratory environment, for example for collecting micro organisms from the liquid sample for subsequent testing. The invention provides a method for filtering a liquid sample which comprises providing a blank of a deformable sheet material and a filtration medium, deforming the blank to form a funnel extending above and about the filtration medium, introducing the liquid sample to be filtered into the so formed funnel, and filtering the liquid sample from the funnel through the filtration medium, for example to a downstream receptacle. The method is accordingly based on the concept that the funnel is not or at least not completely preformed but provided in a form of a blank of a deformable material sheet which is deformed so as to form the funnel at the point and time of use during filtration.
1. An apparatus for filtering a liquid sample, comprising:
a bowl defining a cavity;
a separate blank of deformable sheet material having a peripheral portion and a central portion having an opening;
a filtration medium entirely covering said opening in said central portion of said separate blank of deformable material;
a first holder cooperating with said bowl to hold said peripheral portion of said separate blank of deformable sheet material on said bowl;
a support in said bowl for supporting said filtration medium; and
a piston movably mounted in said bowl, said piston comprising a second holder to hold said central portion of said separate blank of deformable sheet material, said second holder having a plurality of perforations extending therethrough for creating a sub-ambient pressure at the second holder for applying a hold down force to said central portion upon the application of vacuum by a source of vacuum to said second holder; said piston being movable relative to said bowl between a first position in said bowl and a second position in said bowl, wherein when said piston is in said first position, said separate blank of deformable material has a first hold-up volume, and when said piston is in said second position, said separate blank of deformable material has a second hold-up volume, said second-hold up volume being greater than said first hold-up volume, wherein said first hold-up volume and said second hold-up volume are contained by said separate blank of deformable sheet material as a result of moving piston downwards and deforming said separate blank of deformable sheet material.
2. The apparatus according to claim 1 , wherein the cavity of the bowl has an inlet opening and an outlet opening spaced from said inlet opening, and wherein said inlet opening has a larger diameter than said outlet opening.
3. The apparatus according to claim 1 , wherein the support is movable relative to the piston.
4. The apparatus according to claim 1 , further comprising an actuator for separating the filtration medium from the separate blank of deformable sheet material.
5. The apparatus according to claim 1 , further comprising a protective film placed on the separate blank of deformable sheet material.
6. The apparatus of claim 1 wherein the filtration medium is a filtration membrane that is connectable to the separate blank of deformable sheet material in a liquid tight manner.
7. The apparatus of claim 1 , wherein said second hold-up volume is at least 100 ml.
8. The apparatus of claim 1 , wherein said second-hold-up volume is at least 200 ml.
9. The apparatus of claim 1 , wherein said piston comprises a first channel in fluid communication with said plurality of perforations of said second holder.
10. The apparatus of claim 1 , wherein said bowl has an inner peripheral wall, and said piston has an outer peripheral wall, and wherein there is a second channel between said inner peripheral wall of said bowl and said outer peripheral wall of said piston, said second channel being in fluid communication with said source of vacuum.
11. The apparatus of claim 10 , wherein a portion of said outer peripheral wall of said piston abuts said inner peripheral wall of said bowl in sliding engagement.
12. The apparatus of claim 1 , further comprising a first port in fluid communication with said vacuum source and said support, wherein application of vacuum through said first port assists filtration through the filtration medium on the support;
a second port in fluid communication with said vacuum source and said second holder; and
a third port in fluid communication with said vacuum source and the apparatus, wherein the application of vacuum through said third port moves said piston relative to said bowl between said first and second positions.