Patent Publication Number: US-2015076069-A1

Title: Filter vial with limited piston stroke

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application claims the benefit under 35 U.S.C. §119(e) to Provisional Patent Application No. 61/877,872 filed Sep. 13, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Filter vials have a tubular piston with a filter at the distal end of the piston. The piston fits into a mating vial containing a fluid and things suspended in the fluid. When the piston is inserted into the vial fluid passes through the filter and into the piston in order to separate the fluid from particles or molecules too large to pass through the filter in the bottom of the piston. The filtered fluid can be extracted from the piston for further use. In order to maximize the volume of filtered fluid the filter on the piston is placed at the distal end of the piston and during use that filter is pressed against the bottom of the vial in order to force as much fluid through the filter as possible. 
     In order to increase the volume of filtered fluid the piston end and the bottom of the vial may have mating shapes that help ensure as much fluid is forced through the filter as possible. Such mating shapes are described in U.S. Pat. No. 8,322,539. 
     In some processes a material is placed into the vial with the liquid and allowed to dissolve in the liquid so as to absorb undesirable molecules, chemicals or things from the liquid. In these processes when the piston is forced against the bottom of the vial the dissolved materials are forced into the piston filter and that may cause the filter to crack and leak—thereby contaminating the filtered fluid in the piston. Sometimes the dissolved material may be forced through the filter if sufficient pressure is applied on the piston. There is thus a need for an improved filter vial that allows the use of dissolvable materials while avoiding contamination of the filtered fluid in the piston by contact with the dissolved or dissolvable material. 
     BRIEF SUMMARY 
     A filter vial and piston are provided where the vial has a cylindrical wall with a closed bottom and open top and with the hollow, tubular piston therein. The piston has a position stop located and configured to abut a mating position stop on the vial to limit relative movement of the piston and vial. The position stops are located to stop the distal end of the piston away from the bottom of the vial a distance of about 10-30% the height of the vial. That a material to be dissolved in a liquid in the vial and to remove unwanted molecules from the liquid with the piston forcing the liquid through the filter but not squeezing the slurry of material so as to force it into the filter 
     The piston assembly thus has a position stop on it that cooperates with a mating portion of the filter vial to stop the end of the piston from hitting the bottom of the filter vial into which the piston is inserted during use. The length of the filter vial and/or the effective stroke length of the piston assembly are selected so that the distal end of the piston assembly is stopped a predetermined distance from the bottom of the filter vial. A suitable position stop is believed to be an outward extending flange on the piston abutting the upper edge of the filter vial encircling the opening into which the plunger assembly is inserted during use. 
     The filter vial and piston assembly may use a cup which fits over the distal end of the filter to hold the piston filter in position on the piston during use so that all the fluid passes through the filter and none passes around the edges of the filter. The parts forming the piston assembly are preferably integrally molded of one piece of material and may snap together so that there is no contamination from ultrasonic welding. If the parts snap-fit together, appropriates seals are provided to prevent wicking or leakage at the location of the snap-lock joints. 
     There is thus advantageously provided a filter vial apparatus having a longitudinal axis with a tubular vial having a closed bottom, an open top and a sidewall extending therebetween and defining a periphery around the open top. The sidewall has an interior height H between the bottom and the open top. The apparatus includes a tubular piston with opposing distal and proximal ends with at least the distal end being open. The piston has walls defining a hollow interior and at least one seal configured to sealingly engage the sidewall of the vial abut an inner circumference of the sidewall when the piston is inserted into the vial. The piston also has having a position stop extending outward from the piston a distance sufficient to abut the periphery around the open top of the vial. The assembly further includes a piston filter connected to the distal end of the filter and blocking the distal end of the piston so any fluid must pass through the filter to enter the hollow interior from the distal end of the piston. The piston and piston filter form a filter assembly. The position stop is located a distance L from the distal end of the piston assembly where the distance L is less than the height H in order to limit the distance which the piston assembly may be inserted into the filter vial during use. 
     In further variations, the vial sidewall defines a cylindrical interior with a diameter D and the at least one piston seal sealing engages that cylindrical interior. Further, the distance H is less than the distance L by a predetermined amount, which amount is preferably about 10-30% of H and ore preferably about 10-20% of H. The filer may include a vial filter having an upper surface located a distance h from the bottom of the filter vial located and wherein the distance L is less than H−h. 
     In still further variations there are at least three seals, two of which are adjacent the distal end of the piston and all three of which are located and configured to engage the sidewall of the vial when the piston assembly is inserted into the filter vial. Further, a cup may fit over the distal end of the piston to interpose and hold the filter between the cup and the piston. The cup has at least one opening in its bottom through which fluid can flow to the piston filter. 
     There is also provided a filter vial assembly that includes a cylindrical walled vial with a closed bottom and open top connected by a sidewall defining a periphery of the open top. The vial may have a hollow, tubular piston therein with a filter connected to a distal end of the piston to prevent fluid from flowing into the distal end of the piston unless it flows through the piston filter. The filter and piston form a piston assembly. The piston has a position stop located and configured to engage a mating position stop on the vial when the piston assembly is inserted into the vial and advanced a predetermined distance toward the bottom of the piston but before the piston assembly abuts the bottom of the vial. 
     In further variations, the filter vial assembly has a position stop on the piston comprises an outwardly extending projection configured and located to abut the filter vial. The filter vial ma have a vial filter located a distance h from the bottom of the vial and extending across the vial to block the flow of fluid past the vial filter unless the fluid flows through the vial filter. The predetermined distance is then selected so that the piston assembly does not extend past the vial filter during use. 
     In still further variations, the assembly can include a sorbent phase extraction material located between the vial filter and the bottom of the vial. The extraction material may be selected to remove selected molecules, chemicals or compounds from a liquid sample placed into the vial and in which the extraction material can dissolve. A fluid may be placed in the bottom of the vial and the extraction material selected to dissolve in the fluid and remove selected chemicals, molecules or compounds from the fluid. 
     In still further variations, a cup may extend over the distal end of the piston with the filter interposed between the cup and the piston to connect the filter to the piston assembly. The cup may have at least one opening in a bottom of the cup to allow fluid access to the filter. The filter vial may have an interior height H between the filter vial bottom and the periphery defining the open top of the filter vial, and the position stop may be a distance L from the distal end of the piston assembly, such that the distance L is less than H to define a residual volume between the piston assembly and the bottom of the vial. Advantageously, the difference between L and H is about 10-30% of H. Preferably, the difference between L and H is about 10-20% of H. The vial may also include a vial filter having an upper surface located a distance h from the bottom of the filter vial located and the distance L may then be less than H−h. 
     There is also provided a method of filtering a fluid using a filter vial having a cylindrical sidewall defining an open top and having a closed bottom opposite the top, and also having a tubular piston having an open bottom covered by a filter to form a piston assembly. The piston assembly fits into the filter vial to seal against the sidewall and force fluid through the filter and into the body of the piston as the piston filter is advanced toward the bottom of the vial. The method includes the steps of placing a fluid in the bottom of the vial and placing a material in the bottom of the vial where the material is selected to remove chemicals or molecules from the fluid. The order of these steps may be switched. The piston assembly is inserted into the open top of the filter vial and the piston is advanced toward the bottom of the filter vial. The method also includes limiting the distance which the distal end of the piston assembly can advance toward the bottom by causing a position stop on the piston assembly to abut a mating stop on the filter vial, the distance being predetermined. 
     In further variations of the method the distance which the distal end of the piston assembly is inserted into the vial is between about 10-30% of a height H of the interior sidewall of the filter vial. The insertion distance is preferably between about 10-20% of a height H of the interior sidewall of the filter vial. The filter vial may include a vial filter having an upper surface located a distance h from the bottom of the filter vial, with the material being located between the vial filter and the bottom of the vial, and the distance which distal end of the piston assembly is inserted into the vial is limited so the distal end of the piston assembly does not extend past an upper surface of the vial filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which: 
         FIG. 1  is an exploded side view of a piston, retainer and vial; 
         FIG. 2  is a sectional view of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the piston and retainer in an assembled configuration; 
         FIG. 4  is a cross-sectional view of the piston, retainer and vial in an assembled configuration with the piston partially inserted into the vial; 
         FIG. 5  is an end view of the retainer cup of  FIG. 1 , looking from the distal end toward the proximal end; 
         FIG. 6  is an end view of the piston of  FIG. 1 , looking from the distal end toward the proximal end; 
         FIG. 7  is a cross sectional view of a further embodiment of a piston assembly for use with the filter vial of this invention; 
         FIG. 8  is a cross-section of the piston assembly of  FIG. 7  inserted into a filter vial with the piston not abutting a vial filter; 
         FIG. 9  is a cross-section of the piston assembly of  FIG. 7  inserted into a filter vial with the piston abutting a vial filter; 
         FIG. 10  is a schematic view of a kit containing piston assemblies of different stroke length and vials of different height; 
         FIG. 11  is a sectional view a filter vial and plunger assembly with filtered fluid in the plunger; and 
         FIGS. 12   a - 12   f  are further embodiments showing a sub-container extending from a bottom of the vial. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-4 , a tubular piston  10  with a circular cross-section has proximal and distal ends  12 ,  14 , respectively, with a porous piston support  16  located at the distal end  14 . The support  16  advantageously takes the form of radial arms intersecting at a central location on the longitudinal axis  18  of the piston  10 . The terms distal and proximal refer to relative locations of parts along the longitudinal axis  18 , and the terms inward and outward refer to relative directions toward and away from the longitudinal axis  18 . One or more flanges  20  extend radially from the proximal end  12 . A first, proximal seal  22  is located between the proximal and distal ends  12 ,  14 . The first proximal seal  22  extends outward, away from longitudinal axis  18 . A vent hole  24  is adjacent the seal  22  and is preferably located slightly toward the proximal end  12  so as to be between the seal  22  and the proximal end  12  of piston  10  as shown in  FIG. 1 , and preferably between the stop  23  and the proximal end of the piston. 
     Between the seal  22  and the proximal end flange  20  is a position stop  23  that extends outward from the outer side of the tubular piston  10 , away from longitudinal axis  18 . The position stop is located to position the distal end  14  of the piston at a predetermined location relative to the bottom of a vial  42  which is described later. The position stop  23  preferably extends radially outward and advantageously takes the form of a flange similar to flange  20 , encircling the outer periphery of the piston  10  in a plan orthogonal to the longitudinal axis  18 . But the position stop  23  may take various shapes and may comprise a plurality of separate stops having distal edges in a plane orthogonal to the axis  18 . 
     Adjacent to and preferably extending to the distal end  14  is a recessed area  26  having a smaller diameter than that of the body of piston  10  forming a shoulder  27  at the location of the larger diameter portion of the piston body. An outward extending distal piston flange  28  is located adjacent the distal end  14  in this recessed area. An axially extending tip  31  ( FIG. 2 ) is preferably, but optionally provided that encircles the distal end of the piston  10 . The tip  31  preferably has a triangular cross section and is very small. 
     A retainer cup  30  has an inner diameter sized to fit snugly against the piston recess  26 . The retainer cup  30  has proximal and distal ends  32 ,  34 , respectively, with a porous cup support  36  over the distal end  34  and a third, cup seal  38  at the proximal end, extending outward, away from the axis  18 . The support  36  is like the support  16 . A membrane filter  40  fits inside the retainer cup  30  and abuts the cup support  36 . The membrane filter  40  is disc shaped, usually with an axial thickness that is several times smaller than its diameter. In some situations multiple filters  40  can be stacked. An inward extending lip  41  at the distal end  34  of the cup  30  provides an axial support around the periphery of the filter  40 . The tip  31  ( FIG. 2 ) on the distal end of the piston  10  presses the filter  40  against this lip  41  when the parts are assembled. 
     The supports  16 ,  36  preferably take the form of radial struts or spokes extending from the walls of piston  10  or cup  30 , respectively. But the supports  16 ,  36  could take other forms, such a rectangular or square grid work, or a plate with drain holes therein. A spoke with a triangular cross-section is believed suitable, with the apex of the triangle abutting the filter  40  in order to reduce blockage of the filter. Since supports  16 ,  36  abut opposing sides of the filter  40 , a spoke with a triangular cross section will require orientating the apexes so they are toward each other. While four spokes are shown, six equally spaced spokes are believed preferable. Too many spokes block flow through the filter  40 , and too few spokes allow the filter to flex and allow unfiltered fluid to bypass the filter by flowing around the periphery of the filter. The intersection of the spokes at the center is preferably small so as not to block fluid flow through the filter, with a center obstruction of about 0.1 inches for a piston  10  with an inner diameter of about 0.3 inches. The dimensions will vary with the sizes and with the strength of the materials used. 
     A tubular vial  42  has an open proximal end  44  and a closed distal end  46 . The vial  42  is sized and shaped so the retainer cup  30  and piston  10  fit within the vial. The vial  42 , cup  30  and piston  10  are preferably all cylindrical with a circular cross section, but other shapes could be used. The vial  42  has a height H measured from the inside of the closed distal end  46 , to the open proximal end  44  as best seen in  FIGS. 1-2 . 
     Referring to  FIG. 3 , the retaining cup  30  fits over piston flange  28  and abuts the recessed portion  26  on distal end  14  of piston  10  so the piston support  16  abuts membrane filter  40  and preferably presses the filter  40  against lip  41  and against cup support  36 . Ideally the circular tip  31  provides a concentrated force around the periphery of the filter  40  to clamp the filter against the lip. The filter  40  is thus held in position by the lip  41  and tip  31 , and further supported by the supports  16 ,  36 . The tip  31  and lip  41  hold the periphery of the filter  40  in position with the tip  31  providing an axial compression seal against the filter  40 . Movement, such as bowing or twisting of the body of the filter  40 , is restrained by the supports  16 ,  36 . The combination of supports  16 ,  36 , lip  41  and tip  31  are sufficient so that the seal between the periphery of the filter  40  and lip  41  does not leak as filtrate fluid  50  is forced through the filter  40 . 
     As the retainer cup  30  fits over the recessed portion  26 , the flange  28  forces the sidewall  29  of the cup  30  outward to form a fluid tight seal and the proximal end  32  preferably abuts or comes close to shoulder  27 . The piston flange  28  is preferably at or very close to the distal end  14  of piston  10 , and is interposed between the outer wall of piston  10  and the inner wall of the cup  30  to form a fluid tight seal. Advantageously, the piston support  16  presses the filter  40  against the lip  41  enough to prevent any leakage past the end of the filter  30 , and preferably the filter is compressed by the circular periphery of distal end  14  of piston  10 , or compressed by the circular periphery of the support  16 , so that any fluid wicking between the outer periphery of the filter  10  and the wall  29  of the cup  30 , does not enter the cup. The location of the shoulder  27  and the axial length of the sidewall  29  of cup  30  can be selected to achieve a desired amount of compression. 
     As the retainer cup  30  fits over the recessed portion  26  and the seal  26 , the sidewall  29  of the cup  30  is deformed outward so the outer diameter of the assembled cup  30  and piston  10  is slightly larger than the diameter of the piston body  10 . The assembled cup  30  and piston  10  form a piston assembly  43  ( FIG. 3 ) with the distal side of stop  23  located a distance L from the exterior, distal end  34  of the cup  30  which forms the distal end of the piston assembly. The first, proximal seal  22  is located a distance D from that distal end  34 . The length L may be referred to as the stroke length as in the depicted embodiment of  FIGS. 1-7  the length L also represents the distance that the piston assembly is inserted into the filter vial during use. The distal end of the piston assembly  43  preferably has a chamfered periphery in order to make it easier to have automated handlers manipulate the piston assembly  43  and insert it into a vial  42 . Likewise, the vial  42  preferably has an outwardly chamfered opening at the proximal end  44  that makes it easier to insert the distal end of the piston assembly  43 . A chamfer of about 30-45 degrees is believed suitable. 
     To assemble the piston assembly  43  the filter  40  is placed inside the retaining cup  30 . The cup  30  is then snap fit over piston flange  28  and onto the distal end of the piston  10 , and preferably (but optionally) pushed along the piston until an outwardly extend cup seal  38  on the open, proximal end of the cup  30  abuts the shoulder  27  on the piston. At this point the filter  40  is held between the distal end of the piston  10  and lip  41 , and preferably held between the piston support  16  and cup support  36  and lip  41 . This assembly also forms two outwardly extending portions, one at the location where the piston flange  28  forces the sidewall  29  of cup  30  outward, and the other at the location of cup seal  38 . Both of these seal locations are larger than the inside of tubular vial  42  and form two seals with the sidewall of the vial  42  when the relevant portions of the piston assembly  43  are placed inside the vial  42 . Both of these seal locations are preferably separated by a distance sufficient that the wall of the vial  42  extends inward toward longitudinal axis  18  a slight distance in order to ensure a good fluid-tight seal at both locations. 
     During use, the piston assembly  43  is fit into vial  42  to force fluid or filtrate  50  through the filter  40  and into the hollow interior of the tubular piston  10 . Preferably, but optionally, the piston flange  28  bulges the sidewall  29  of cup  30  outward enough to form a fluid tight seal with the inner walls of vial  42 . The seal  38  is also sized relative to the inner walls of vial  42  to form a fluid tight seal with the vial. Advantageously, there are thus two outward facing seals adjacent the distal end  14  of the piston  10  which seal against the interior walls of vial  42 . 
     During use, a material  49  and liquid  50  are placed in the bottom of vial  42 . The material  49  may be selected to interact with the liquid  50  and bind to selected portions of the liquid, be they specific molecules, gases, chemicals or compounds either by adsorption, absorption, ionic binding or other attachment mechanisms. The material  49  is preferably selected to absorb selected one or more selected portions of the liquid  50  and may be referred to as a selective binding material for convenience. Preferably, the material  49  comprises a material that removes unwanted or undesirable things from the liquid  50 . The material  49  may comprise a sorbent phase extraction material selected to absorb undesirable portions of the liquid  50 . The material  49  is preferably a solid material and may be a powder, granular or larger block sized materials. 
     The material  49  and liquid  50  are typically left in the vial  42  for a period of time that can vary but is typically from about 1 to 48 hours more typically about 24 hours. In some cases it may be a matter of a few minutes to a few hours, but it is usually longer. The exact time will vary with the particular liquid  50  and material  49  involved. During this time the material  49  usually dissolves in the liquid  50  and forms a slurry of smaller particles intermixed with the liquid  50 . The removable cap  52  may be placed over the open proximal end  44  of the vial during this period to avoid contamination and to allow shaking or other agitation of the contents of the vial  42  so that the material  49  and liquid  50  are well intermixed. The amount of agitation, if any, will vary with the liquid  50  and material  49 , as will the temperature and other processing conditions. Instead of a removable cap  52 , the piston assembly  43  may be inserted sufficiently into the open end  44  of the vial  42  to seal the end of the vial and enclose the material  49  and liquid  50  within the vial  42 . 
     After the material  49  and liquid  50  are suitably mixed the piston assembly  43  is used to separate the desired liquid from the material  49 . The cap  52  is removed (if present) and the distal end of the piston assembly  43  is placed in the open end  44  of the vial  42 . The piston  10  is then advanced along longitudinal axis  18  so that fluid or filtrate  50  passes though filter  40  and into the body of piston  10 , with air or other gases escaping through vent  24 . Eventually the seal  22  enters the vial  42  and also seals against the inner walls of vial  42 . Filtrate  50  passing through the filter  40  is in the hollow body of piston  10  where it can be removed directly, or through an opening in cap  52  which is fitted over the proximal end  12  of the piston  10 . Materials entrained in the filtrate  50  which are too large to fit through the filter  40  are retained between the filter  40  and the closed distal end  46  of the vial. Preferably the cap  52  forms a snap fit with the proximal end of the piston  10 , and more preferably has an inwardly extending rim or lip that forms a snap-fit over flange(s)  20  on the piston  10 . 
     In the preferred separation a portion of the liquid  50  is left intermixed with the material  49  so that a slurry remains and a portion of the liquid  50  is not forced through the piston filter and into the piston  10 . The piston  10  and vial  42  are configured thus so that the distal end of the piston assembly  43  does not abut the bottom  46  of the vial  42  and does not compact the slurry so as to separate as much liquid as possible from the solid material  49  and compact the remaining material  49  into a contiguous, but wet mass of material at the bottom of the vial. Advantageously, the piston assembly does not compact the material  49  so as to force portions of the material into the porous filter(s) of the piston assembly  43 . In some cases the liquid  50  and material  49  intermix and then over time the material settles out on the bottom of the vial  42 , leaving a purified liquid above the settled material and in such cases the filter  40  on the piston is stopped before abutting the material  49  settled on the bottom of the vial. In some cases the liquid  50  and material  49  remain in a slurry and as the piston advances toward the bottom of the vial the piston assembly  43  forces the liquid  50  through the piston filter  40  while moving a portion of the material  49  toward the bottom  46  of the vial to separate the fluid from the material. As the piston advances the slurry becomes thicker as liquid  50  passes through the piston filter  40  and eventually a bed of material  49  with little liquid  50  will be forced against the bottom  46  by the piston filter  40 . The amount of liquid  50  remaining in the compacted bed of material  49  will vary with the size of the particles forming the bed and the nature of the stuff being removed from the liquid  50 . It is believed undesirable to advance the piston a distance sufficient to force 80-90% of the liquid  50  pass through the filter. It is believed more desirable to have about 75% or less of the liquid pass through the piston filter  40 , and preferably to pass about 25-50% of the liquid  10  through the piston filter  40 . 
     Advantageously the stop  23  on piston  10  hits the proximal end  44  of the vial  42  to position the piston  10  relative to the vial  42 . Thus, the distance L between the position stop  23  and the bottom  46  on the inside of vial  42  is shorter than the distance H. It is believed preferable to have the distance between the distal end of the piston assembly  43  and the bottom  46  of the vial  42  is between about 10% and 30% of the height H of the vial  42 . The distal end of the piston assembly  43  and bottom  46  of vial  42  thus define a residual volume which may contain the material  49  and any remaining liquid  50 . A distance of about 10% to 20% of the height H of the filter vial  42  is believed more preferable. But the distance between the distal end of the piston and the bottom of the vial will vary with the particular material  49  and liquid  50  being used. A minimum distance of at least 1-5 mm is believed desirable for most applications. In many applications a vial  42  having an internal diameter of about 3-9 mm and a height of about 32 mm is believed suitable. 
     Advantageously, the proximal seal  22  is sealingly engaged with the inner sidewall of the vial  42  when the position stop  23  abuts the end  44  of the vial  42 . This provides further assurance that the material  49  and the portions of the liquid  50  entrapped by the material  49  remain in the vial  42  while the filtrate can be removed from the hollow body of the piston  10 . Thus, the distance D ( FIG. 3 ) is preferably less than the distance H as well as being less than the distance L. 
     Other seal types could also be used for seals  28 ,  22 ,  38 , but are believed less desirable. For example, O-ring seals set in rectangular or semi-circular recesses could be used. But the seals  28 ,  22 ,  38  are preferably integrally molded or cast with the parts from which they extend. Further, the preferred piston  10 , cup  30  and vial  42  are molded out of various plastics and that makes forming suitable recesses to hold the O-ring or even D-ring seals difficult because the recesses reduce the strength of the parts. The piston  10 , cup  30  and vial  42  are preferably molded of a suitable plastic, preferably one that does not contaminate samples placed in the vial  42 . The vial is preferably made of polyolefin, preferably polypropylene, or other suitable polymer. The filter  40  is preferably, but optionally made of Teflon, nylon, glass fiber or other filter materials such as PVDF (polyvinyldifloride) or PES (polyethersulphone), etc. 
     A fill line  54  is optionally placed on the outside of the vial  42  to indicate a maximum level of fluid placed inside the vial when the material  39  is in the vial. The walls of the vial are preferably sufficiently transparent or translucent so the placement of fluid inside the vial  42  can be seen from outside the vial to allow use of the fill line  54 . The fill line  54  can be molded into the vial as an outwardly extending flange or inwardly extending recess, or the fill line can be marked by paint, marker, abrasion, laser etching, chemical etching, or other process leaving a visible indicia. 
     Referring to  FIGS. 7-9  and  11 , a further embodiment is shown having tubular piston  10 ′ with outwardly extending position stop  23  and a first proximal seal  60  formed by an O-ring held in a groove formed by two circular flanges extending outward from the piston  10 ′ a distance less than the diameter of the O-ring. A second seal  62  is located adjacent the distal end of the piston  10 ′ and preferably comprises an O-ring held in a groove formed by two circular flanges extending outward from the piston  10 ′ a distance less than the diameter of the O-ring. The distal end of the piston  10  has an inward facing recess  64  on the inside of the tubular piston with that recess sized to receive filter  40 . The filter  40  may be a disc shaped filter and may be press fit  64  into the recess  64  or otherwise fastened to the distal end of the piston  10 ′. The filter  40  blocks the distal end of the tubular piston  10 ′ so that any fluid flowing into the interior of the tubular piston passes through the filter  40 , as in the first embodiment of  FIGS. 1-6 . 
     The piston  10 ′ is sized to fit inside the vial  42  with the seals  60 ,  62  forming fluid tight seals against the interior sidewall of the vial. The piston  10 ′ may be used as in the first embodiment to seal against the sidewall of the vial  42  and force fluid through the piston filter  40  as the tubular piston is advanced toward the bottom  46  of the vial  42 , with the stop  23  limiting relative motion between the piston and the vial so the distal end of the piston is spaced a predetermined distance from the bottom of the vial. 
     The vial  42  preferably has a retaining device to retain a vial filter  66 . The retaining device may take the form of an inwardly facing recess  68  extending away from the axis  18  and into the sidewall of the vial  42 , or an inwardly extending protrusion  70  extending toward the axis  18  from the sidewall of the vial, or both. A small circular rib is believed suitable for the protrusion  70  and an annular recess is believed suitable for the recess  68 , with the recess and protrusion configured to hold vial filter  40  in a predetermined location in the vial. Advantageously the protrusion  70  and/or recess  68  form a snap-lock to hold the vial filter  66  in place. 
     The vial filter  66  extends across the entire vial  42  and is offset a predetermined distance from the bottom  46  of the vial. Any fluid on the distal side of the vial filter  66  must pass through the vial filter  66  to get to the proximal side of the vial filter. The vial filter  66  has an upper surface that is located a distance h from the bottom  46  of the filter vial  12 , and is orthogonal to the longitudinal axis  18 . 
     During use the material  49  is placed in the bottom of the filter vial  42 , with the vial filter  66  being placed into the vial thereafter and snapped into position where the filter is held. The vial filter holds the material  49  in position. This allows vials to be prepared with a predetermined amount of material  49  in the vial, with the vial filter  66  configured to prevent the material  49  from passing the filter  66 . The liquid  50  may be added before the vial filter  42 , but is preferably added afterwards. If the liquid  50  is added after the vial filter then the vial filter has to be selected to allow the liquid to pass through the filter along with any compounds to be retained by the material  49 . The liquid  50  must be above the level of the vial filter  66  at least during filtration by the piston  10 . If the liquid is below the vial filter  66  additional liquid may be added to mix with and dilute the slurry formed by the material  49  and the preexisting liquid. After the liquid  50  and material  49  are in contact a sufficient amount of time the piston  10 ′ is inserted into the vial  42  and advanced toward the bottom  46  of the vial to force the liquid through the piston filter  40  and into the hollow body of the tubular piston  10 ′. The stop  23  is located to stop the distal end of the piston  10 ′ before it reaches the vial filter  66 , although in some circumstances the distal end of the piston may abut the vial filter. Thus, the stroke length L of the piston assembly  43  is less or equal to than H−h. 
     Because the amount of the material  49  may not be known until the vial is used, it may not be known how much volume is required in the bottom of the vial, and that means it may not be known where the piston  10 ,  10 ′ should stop. It is thus desirable to provide kits having plungers with a variety of different stroke lengths L or vials having a different height as reflected in  FIG. 10 . Thus pistons with lengths of L 1 , L 2  or L 3  may be used with different length vials having interior lengths or heights H 2  or H 3 , recognizing that the length L is selected to be shorter than the length H when the parts are collected to form a kit, so that the material  49  is not forced into the filter  40 . Thus, preferably the kits of plungers and vials are selected such that two or three different stroke lengths L are provided for a single filter vial, or several filter vials of varying heights H are provided for a single piston of length L, with none of the stroke lengths L and vial heights H being such that the distal end of the piston assembly would abut the bottom of the filter vial during use, and instead would have a minimum, predetermined distance between the vial&#39;s bottom and the end of the piston assembly to define a residual volume. 
     Advantageously the pistons  10  and vials  42  are selected such that there is always room at the bottom  46  of the vial. As reflected in  FIG. 10 , three pistons L 1 , L 2  or L 3  of different length provide three different residual volumes if used in the same vial  42 . Likewise, the use of vials  42  with interior cavities of different height H may be used with the same length piston  10  to achieve different residual volumes between the bottom of the piston assembly  43  and the bottom  46  of the vial  42 . Advantageously, the kits have a single piston  10  and a plurality of vials  42  of different interior height H, or the kits have a single vial  42  and a plurality of piston assemblies  43  of different height H. In such cases, the piston assemblies  43 , the vials  42 , or both, are marked, preferably with printed indicia such as numbers, to reflect the residual volume achieved if the piston and vials are used together. This printed indicia may include color coding or marking a volume indicator on the side of the piston or vial or piston or piston assembly. For example, a set of three piston assemblies  43  and one vial  42  of a first color may have a different piston assemblies  43  marked with one of the numbers 5, 10 and 15 to reflect the residual volume in the vial when the selected piston is used with the vial of the same color. Likewise, three vials  42  and one piston assembly  43  all of a second color may have similar numbers on the vials to reflect the residual volume when used with the piston. Piston assemblies and vials of different colors may have printed indicia of different colors indicating the residual volumes when a piston assembly is used with a vial of the color in which the printed indicia (number) appears. There are a variety of ways to coordinate pistons and vials having different lengths L and heights H to achieve different residual volumes reflected by height h. For simplicity, and cost, kits with only a few extra piston assemblies of different length for one vial, or a few vial of different length for one piston, are preferred. Preferably there are fewer than five, and more preferably only one or two different length piston assemblies for each vial or different length vials for each piston assembly. 
     There is also provided an improved method of separating liquids. Referring to  FIGS. 1-4  The method includes placing the material  49  in the bottom of a vial  42  and placing the liquid  50  in the bottom of the vial. The vial may have liquid  50  in it when the material is added or the liquid may be added after the material  49 . The material  49  is selected to remove things from the liquid such as chemicals, molecules, gases or other things. The material  49  and liquid  50  are left together a suitable time for the removal to occur completely or to a desired extent, or left for a predetermined time. Typically they form a slurry as the material  49  falls apart in the liquid. The liquid is then separated from the material  49  by the piston assembly forcing liquid  50  through the piston filter  40  and into the body of the piston  10  from which the filtered liquid can be removed. 
     Referring to  FIGS. 8-10 , the method may include placing material  49  in the bottom of the vial  42  and then placing vial filter  68  in the vial to hold the material in position. The vial and material may be then used, or the method may include placing a cap  52  ( FIG. 2 ) over the open, proximal end of the vial and either storing the assembly or shipping the vial and material. Instead of the cap  52 , the distal end of a piston assembly  43  may be inserted into the vial a distance sufficient to hold the parts together while allowing removal of the piston assembly later. A liquid may be added to the previously prepared sub-assembly of the vial and material, with the liquid passing through the vial filter  66 . That means the filter  66  has to be selected for certain liquids or that only certain liquids may pass through the filter. The material  49  is selected to remove things from the liquid such as chemicals, molecules, gases or other things. The material  49  and liquid  50  are left together a suitable time for the removal to occur completely or to a desired extent, or left for a predetermined time. Typically they form a slurry as the material  49  falls apart in the liquid. The vial filter  66  preferably does not allow the material  49  to pass, but the filter  66  may be a simple frit or porous mesh sufficient to restrain passage of solid material  49  but sufficiently porous to allow passage of material  49  when dissolved in or mixed with liquid  50 . The method then includes separating the reacted liquid from the material  49  by moving the piston and vial relative to each other so the piston assembly forces liquid  50  through the piston filter  40  and into the body of the piston  10  from which the filtered liquid can be removed. Preferably the distal end of the piston assembly  43  does not abut vial filter  68 , but it may. The method may also include holding the vial filter in place and thus holding the solid material  49  in the volume defined between the vial filter  66  and the bottom  46  of the vial  42 , at least until the liquid  50  is added. 
     The vial  42  and piston assembly  43  provide a multi-tier filtration device allowing for total solids, resins, glass beads, and other semi-solid or total solid materials to be placed at the bottom of the filter vial  42  while giving enough clearance to do multiple extractions in one device. Previously, users with pills had to crush their pills in a mortar and pestle and then dump the components that may not be uniformly dissolving into the filter vials for dissolution testing, solubility, or friability testing. With the present invention a user can drop the pill into the bottom of the vial  42 , or drop in multiple pills—without the need to crush them. The assembly allows for the pills to dissolve, or the user may add different agents for different functional testing. 
     There is thus provided a filter vial  42  with an internal cavity within which a user can perform secondary or tertiary manipulations and that allows for the eliminations of multiple vessels before the final sample extraction. Another example of the advantageous use of this invention would be with the material  49  comprising resins (e.g., quechers, different salts, spe, micro beads, luminex beads, binding beads, etc.) that trap what is not wanted to be tested from such samples  50  as proteins, matrices like food, urine, plasma, etc. After the filter vial  42  is filled with a given amount of these resins  49  and liquid  50  contain the sample to be tested, and after a suitable time is provided for removing unwanted things from the sample  50 , then the final filtration may be performed within the vial by forcing the liquid through the piston filter  40  and into the body of the piston  10  where it may be removed for further use. This allows for what was previously a multi-step or component filled transfer to be performed in one vessel, vial  10 . This allows for minimization of step error, and maximization of product integrity. 
     Using the vial  10  and piston assembly  43  of this invention, a filter vial for biologic extraction of DNA and protein extraction could be used in the cell, seed generation testing of genetic markers, by having multiple cells/seeds or single cell/seed broken added as the material  49  within the vial  42  and then adding different buffers as the liquid  50 , with the combination or residual (filtered) liquid to come through the piston filter  40  and into the body of piston  10  for use. 
     The device can be used with bead beaters, paint shakers, and multiple type of disrupting machines to break-up clumps or solids within the matrices. The distal end could be used with a lead-in that would allow for easy insertion by automated robots for use in full automation of products. The plunger design could be made with multiple bottom shapes, and the interior of the bottom could be triangles, squares, and other shapes that allow for different current testing to be moved into this device. 
     Referring to  FIGS. 12   a - 12   c , in further variations, because the distal end of piston does not enter the bottom-most portion of the vial  42 , that bottom portion may have various shapes, especially on the inside of the vial. Thus, while the upper portion of the vial  42  is preferably cylindrical to provide good fluid seals as the piston assembly slides along the inside of the vial, the bottom portion of the vial may have any of a variety of shapes, and may contain shapes within it, or extending from the bottom  46 . Thus, the bottom portion of the vial may have an inset  80  having a square walled shape extending from the bottom  46  or sidewall of the vial ( FIG. 12   a ,  12   d ), or a short-walled cylindrical shape extending from the bottom  46  ( FIG. 12   b ,  12   e ), or a triangular shape as in  FIG. 12   c ,  12   f . It is believed advantageous if the shape of these interior walled portions  80  are sized to enclose a predetermined volume so that the volume enclosed by the shape  80  could be used to measure and hold a predetermined amount of material  49  placed in the walled volume. The walled shapes thus form sub-containers  80  of predetermined volume to measure the material  49 , with the sub-containers  80  extending inward from the bottom  46 , or extending outward along axis  18  from the bottom  46  but being in fluid communication with the inside of the vial. 
     The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein, including various ways of forming the seals between the piston  10 ,  10 ′ and the inside of the vial  42 . Likewise, various ways may be used to limit relative motion of the piston and vial in order to correctly position the distal end of the piston. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.