US3873449A

US3873449A - Filter skimming apparatus

Info

Publication number: US3873449A
Application number: US348372A
Authority: US
Inventors: John J Connelly; Stefano Alan A Di
Original assignee: Baxter Laboratories Inc
Current assignee: Baxter International Inc
Priority date: 1973-04-05
Filing date: 1973-04-05
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: CA1025179A; GB1455523A

Abstract

Filter skimming apparatus comprising an elongated concave plunger arm adapted for telescopic insertion in a test tube. The plunger arm has an inverted cup-shaped piston head at the lower end for holding a filter element and having a rim for slidable sealing engagement of the inner walls of the test tube.

Description

United States Patent Connelly et a1.

FILTER SKIMMING APPARATUS Inventors: John J. Connelly, San Juan Capistrano; Alan A. Di Stefano, Rialto, both of Calif.

Baxter Laboratories, Inc., Morton Grover, 111.

Filed: Apr. 5, 1973 Appl. No.: 348,372

Assignee:

U.S. Cl 210/359, 23/259,210/D1G. 23 Int. Cl 301d 33/00 Field of Search 23/259; 210/359, D16. 23;

References Cited UNITED STATES PATENTS 12/1969 Farr 210/359 2/1970 Mass 210/1316. 23

I Mar. 25, 1975 3,512,940 5/1970 Shapiro 23/259 3,586,064 6/1971 Brown 23/259 X 3,661,265 5/1972 Greenspan 210/359 3,693,804 9/1972 Grover 210/359 3,802,843 4/1974 Kim 23/259 Primary ExaminerMorris O. Wolk Assistant ExaminerSidney Marantz Attorney, Agent, or FirmScott J. Meyer; Louis Altman [57] ABSTRACT Filter skimming apparatus comprising an elongated concave plunger arm adapted for telescopic insertion in a test tube. The plunger arm has an inverted cupshaped piston head at the lower end for holding a filter element and having a rim for slidable sealing engagement of the inner walls of the test tube.

2 Claims, 13 Drawing Figures PZJENTED 3,873 ,449

sum 2 o 3 FILTER SKIMMING APPARATUS This invention relates to an improved filter skimming method and apparatus and, more particularly, to a method and apparatus for the separation of blood serum or plasma from suspended cells and other particulate matter.

The separation of serum or plasma from centrifuged, clotted or whole blood specimens is a common clinical procedure. Various filter skimming devices have been adapted for such use. These devices are conventionally provided in the form of two telescoping tubes in which the outer tube is an initial blood collection test tube and the inner tube is a plunger tube which serves as a pressure or vacuum filter and collects the supernatant liquid as the plunger tube is depressed into the outer test tube. The plunger tube is provided with a filter at the bottom to occlude cells from the supernatant liquid during the skimming of the supernatant blood serum or plasma from the suspended cells.

Illustrative of the foregoing filter skimming devices are those such as described in US. Pat. Nos. 3,355,098; 3,481,471; 3,512,940; 3,661,265; and 3,693,804.

It is an object of the present invention to provide an improved filter skimming method and apparatus.

It is another object of this invention to provide a novel filter skimming method and apparatus for improved separation of blood serum or plasma from suspended cells and other particulate matter.

It is still another object of this invention to provide a conveniently accessible test tube size filter skimming apparatus comprising a thumb operable filter skimming plunger which is adapted to be telescopically inserted in a blood collection test tube whereby the resulting supernatant liquid can be readily decanted after filtering.

These and other objects will be apparent to the person skilled in the art after reading the specification and claims hereof.

Briefly stated, the filter skimming apparatus of this invention comprises an elongated concave plunger arm adapted to be telescopically inserted in a test tube, an inverted cup-shaped piston head at the lower end having a small bore opening at the top for allowing passage of supernatant liquid and a peripheral rim at the bottom for slidable sealing engagement of the inner walls of a test tube, and a lower cup having a small bore probe at the bottom for allowing entrance of fluid specimen and an upper open cavity for retaining a filter element, the outer walls of said cup adapted for engagement of the inner walls of said cup-shaped piston head.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed that the invention will be better understood from the following exemplary description taken in connection with the accompanying drawings in which:

FIG. 1 is an exploded view showing the elements of the filter skimming device of the invention.

FIG. 2 is a perspective view showing the filter skimming device in operation.

FIG. 3 is an end view of the plunger of the filter skimming device showing the concave arm section, the peripheral rim and the small bore opening at the top of the piston head.

FIG. 4 is a side elevational view of the plunger in cross-section taken along the line 44 of FIG. 3 showing the elongated, concave arm and the lower cupshaped piston head.

FIG. Sis an end view of the cap of the filter skimming device showing the offset small bore probe.

FIG. 6 is a side cross-sectional view of the filter cup taken along the line 66 of FIG. 5 showing the small bore probe at the bottom and the upper open cavity.

FIG. 7 is a side view of a filter element for placement in the filter cup of FIG. 6.

FIG. 8 is a top view of the filter element of FIG. 7.

FIG. 9 is an end view ofa plunger in another embodiment of the invention.

FIG. 10 is a side elevational view of the plunger in cross-section taken along the line l010 of FIG. 9.

FIG. 11 is a side elevational view of a plunger in still another embodiment of the invention.

FIG. 12 is a front elevational view of the plunger of FIG. 11.

FIG. 13 is an enlarged fragmentary side crosssectional view of the plunger of FIG. 11 showing the piston head assembly with the filter cup and filter element.

Referring now to the drawings and particularly to FIG. 1, the filter skimming apparatus comprises plunger 10, a filter cup 20, and a filter element 26. Plunger 10 has a relatively thin, for example l2 mm. thick, elongated arm 11 with side edges 12, an inverted cupshaped piston head 13 at the lower end having a cavity 14, a top 15, and a lower peripheral rim 18 which is adapted for slidable sealing engagement of the inner walls of test tube 29. Piston head 13 has a small bore opening 17 preferably extending throughout a relatively short, upwardly disposed tubelike extension 16 and centered at the top 15 of piston head 13.

Filter cup 20 has a cavity 21, a bottom 22 and a probe 23 having a small bore opening 24 and extending downwardly and preferably offset from the center of the bottom. Probe 23 preferably has a beveled edge such as at a 45 angle at opening 24. The outer diameter of filter cup 20 is such that the cup will fit tightly in piston head 13.

Filter element 26 has a top surface 27, a bottom surface 28 and is suitably proportioned for placement in the cavity 21 of filter cup 20, which in turn is adapted for insertion in'the cavity 14 of piston head 13. The diameter of filter element 26 is such that the filter will fit tightly in filter cup 20.

FIGS. 3 and 4 show the plunger 10 in greater detail. The elongated arm 11 preferably gradually tapers in width as it extends from the piston end to the distal end. Greater width is preferred at the piston end due to stresses in operation of the plunger. Arm 11 is generally concave on its inner side to allow convenient thumb and finger gripping and can also have a spoon shaped handle configuration.

The piston head 13 has a small bore opening 17 to allow upward passage of supernatant fluid. The bore preferably is about 0.03 to about 0.05 and most preferably about 0.04 inch in diameter. Piston head 13 preferably has a relatively short tubelike extension 16 to allow a steady upward flow rather than squirting of supernatant fluid through opening 17. Thus, in an exemplary plunger arm having an overall length of about 4 inches, the extension I6 can be from about one-half to about one inch and preferably about three-fourth of an inch in height. The opening 17 is centered in the top I5 of piston head 13 to allow an even flow of supernatant fluid from cavity 14.

FIGS. 5 and 6 show the filter cup in greater detail.

The probe 23 has a small-bore opening 24 generally of about the same diameter as opening 17. Probe 23 is of a length suitable for extending downwardly through the surface of the fluid specimen in test tube 29. A small fraction of an inch such as about one-eighth to about three-eighths and preferably about one-fourth inch one-eighth is a sufficient length for convenient operation of the plunger. Probe 23 preferably has a beveled edge which can be at about a 45 angle for optimum cutting into the depth of the supernatant fluid. Probe 23 also preferably is positioned offset from the center of bottom 22 of cup 20 and is thereby adapted to reach into an extensive portion of the fluid specimen as the plunger 10 is gradually twisted in test tube 29.

Filter cup preferably has an annular projection which forms a ridge on the inner bottom of the cup. Filter element 26 preferably is proportioned to seat on projection 25 and has a thickness substantially equivalent to that portion of the height of cup 20 above said projection 25. Piston head 13 similarly preferably has an annular projection 19 which forms a ridge on the inner top of the piston head with a diameter substantially the same as the diameter of filter cup 20. Projection 19 thereby restrains filter cup 20 from seating flush against the inner top of piston head 13. Thus, neither cavity 21 nor cavity 14 is completely filled with the filter element 26 and a pair of small, residual cavities are formed below the bottom surface 27 and above the top surface 28 of filter element 26. The lower said residual cavity allows the intake of fluid specimen through probe 23 to be evenly dispersed over entire bottom surface of filter element 26 and the upper said residual cavity allows for uniform dispersion of the fluid specimen through the filter element 26 and similar uniform collection of the filtered supernatant fluid at the top prior to its exit through opening 17.

FIGS. 7 and 8 show the filter element 26 prior to assembly in filter cup 20. The filter element 26 is gener' ally cylindrical and can be fabricated of various suitable filter materials such as glass-wool, asbestos, or synthetic plastic fibers, for example, compacted polypropylene or other such polyolefin fibers; porous ceramic or other such inert inorganic filtering materials, for example, sintered glass and diatomaceous silica; porous plastic substances such as polyurethane elastomeric foam and porous polyethylene. The pore size of the filter element preferably is such as will effectively filter all fibrin strands from a blood sample.

FIGS. 9 and 10 show another embodiment of the plunger. In this embodiment, the small bore opening 37 is positioned offset from the center of the top 35 of piston head 33 and a relatively short tubelike extension 36 traverses the lower end of elongated arm 31 intermediate side edges 32. The supernatant fluid which collects in the top part of cavity 34 will thus flow through opening 37 and thence down the inner side of elongated arm 31. In this embodiment, arm 31 will have a greater thickness at the piston end to allow space for tube 36 within the confines of the arm. Tube 36 will have about the same height as tube 16 in the embodiment of FIGS. 3 and 4. Rim 38 and projection 39 correspond, respectively, to rim 18 and projection 19 in the embodiment of FIG. 4.

FIGS. 11, 12 and 13 show still another embodiment of the plunger. In this embodiment, short tubelike extension 46 is positioned on the inner concave side of plunger arm 41 intermediate both side edges 42. Piston head 43 has a lower peripheral rim 48 and a partial peripheral upper rim 49 opposite the concave portion of arm 41, both of which rims make slidable sealing engagement of the inner walls of a test tube.

FIG. 13 shows the piston head assembly in which filter element 53 is positioned in the cavity of filter cup 51, which in turn is positioned in cavity 44 of piston head 43. Annular projection 50 on piston head 43 restrains filter cup 51 whereby cavity 55 is formed between the top 45 of piston head 43 and the top of filter element 53; annular projection 52 on filter cup 51 similarly restrains filter element 53 whereby cavity 54 is formed below filter element 53.

In the embodiment shown in FIG. 13, arm 41 has a small transverse opening 47 at the top of tubelike extension 46 whereby fluid can be ejected on either or both sides of arm 41. In probe 56, the angle of the beveled edge at opening 57 faces the opposite direction from that shown in the embodiment of FIG. 6. In assembly, probe 56 is in substantial vertical alignment with tubelike extension 46. To facilitate this alignment in operation, the outer wall of filter cup 51 and the inner wall of piston head 43 can be provided with a vertically disposed keyway and a mating rib on either wall.

In still another embodiment of the present invention, the rim 18 for slidable sealing engagement of the inner walls of test tube 29 can be provided on the periphery of bottom 22 of filter cup 20 instead of piston head 13.

Tubes

16, 36 and 46 preferably are of a clear material such as a transparent plastic so that the operator can determine whether any cells are being collected in the filtered supernatant liquid. The entire plunger 10 can be conveniently fabricated of polyolefin plastic, for example, polyethylene and polypropylene and other such plastic materials.

In the operation of the apparatus and in practicing the method of the invention, as can best be seen from FIG. 2, the operator will grasp the distal end of plunger 10 with the thumb positioned in the concave side of elongated arm 11 and slowly depress the plunger into test tube 27 until probe 23 reaches through the top surface of the fluid specimen. Due to the slidable sealing engagement of rim 18 with the inner walls of the test tube, pressure will be created which forces the serum or plasma 61 into piston head 13 which contains the filter element. The filtered supernatant liquid will then be forced through opening 17 and collect in the top of test tube 27 above the rim 18. Plunger 10 can be depressed in the fluid specimen to the extent desired and generally so that probe 23 continuously extends into the supernatant fluid as the fluid is being forced through the filter and until it finally reaches the surface of the red cells 60 packed at the bottom of the test tube. Rotation of plunger 10 having an offset probe 23 will ensure collecting supernatant liquid trapped in any fibrin strands. After the entire portion of the supernatant liquid has passed through the filter element and into the upper part of test tube 27, the filtered supernatant liquid can be readily collected by decantation into another test tube or similar such storage container or it can be aspirated such as with a pipette.

The present invention has several unique advantages over filter skimming devices of the prior art. In the present device the filtered sample can be retained within the walls of the same test tube in which it was contained prior to filtering whereas in prior devices a separate telescoping inner collection tube is generally required.

The lower probe on the filter cup in the present device, in addition to its function of reaching into the fluid specimen, is adapted to serve as a vent which is in alignment with the upper tubelike extension on the plunger arm to allow entrance of air below the piston head so that the plunger arm can be more readily withdrawn from the test tube than the telescoping inner collection tubes of prior devices.

Not only is the present device suitable for manual use but also it is well adapted for semi-automatic use such as on the sample turntables of automated analytical instruments, for example, the Technicon AUTOANA- LYZER. In such use, the sample on the turntable can be directly aspirated out of the Vacutainer or sample tube by the sampler probe. This can be done without removal of the plunger arm.

In the preferred embodiment of FIGS. 11, 12 and 13, the present invention has a unique plunger pull-out feature. By tilting the entire sample test tube, the plunger arm with the transverse opening 47 can be withdrawn in such a mananer that the supernatant filtered fluid is easily and entirely retained above the lower unfiltered material. In prior devices there generally is a continuum of fluid and withdrawal of the inner telescoping collection tube tends to cause back filtration.

In order to facilitate prevention of contamination of the filtered serum sample, the plunger arm (e.g., arm 11) can be provided with a lower cylindrical portion having a diameter about the same as that of the piston head (e.g., piston head 13) anda height greater than that of the tubelike extension.(e.g., extension 16).

While particular embodiments of the invention have been illustrated and described herein, it will be obvious to those having skill in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and it is intended to cover in the appended claims all such changes and modifications.

What is claimed is:

1. Filter skimming apparatus comprising a plunger having an elongated arm, an inverted cup-shaped piston head, a filter cup disposed in said piston and containing a filter element, said piston head having an annular projection on its inner top and said filter cup having an annular projection on its inner bottom whereby a cavity is formed above said filter element and a second cavity is formed below said filter element, said piston head having an upwardly disposed, small bore tubelike extension and said filter cup having a downwardly extending, small bore probe offset from the center of the bottom of said filter cup, said plunger having a peripheral rim at the piston zone adapted for slidable sealing engagement of the inner walls of a test tube.

2. The filter skimming device of claim 1 in which the tubelike extension is offset from the center of the top of said piston head toward the inner side of said elongated arm, the elongated arm is concave on its inner side and contains a small transverse opening at the top of said tubelike extension, and said peripheral rim is positioned on the lower extremity of said piston head. l= =l

Claims

2. The filter skimming device of claim 1 in which the tubelike extension is offset from the center of the top of said piston head toward the inner side of said elongated arm, the elongated arm is concave on its inner side and contains a small transverse opening at the top of said tubelike extension, and said peripheral rim is positioned on the lower extremity of said piston head.