Universal outlet for filter units

Filter device comprising a filter housing, a filter disposed in the filter housing, an inlet, and an opposed outlet spaced from the inlet, wherein the outlet comprises an extension from the housing, the extension extending longitudinally in the direction of fluid flow and comprising at least a first section having a minimum outer diameter and a second section downstream from the first section and having a terminal end having a maximum outer diameter, the maximum diameter of the second section terminal end being smaller than the minimum diameter of the first section.

BACKGROUND OF THE INVENTION
 Filtration of solutions is generally desired to remove particles in sample
 preparation applications, analytical techniques and prior to an
 instrumentation analysis, for example, or to sterilize a solution in
 tissue culture applications. Depending upon the volumes that need to be
 filtered, different syringe driven filter sizes, identified by their
 filter diameter, are available. These include 4 mm, 13 mm and 25 mm sizes.
 The 4 mm syringe driven filters are typically recommended for the
 filtration of volumes less than or equal to 1 ml.
 Conventional syringe drive filters have male and female luer taper fittings
 designed to mechanically connect two medical devices such as a syringe and
 a needle. As shown in FIG. 1, most conventional syringe driven filters
 have a female luer lock inlet and male luer slip outlet. The female luer
 lock inlet ensures that the filter is securely (but removably) attached to
 the outlet of the syringe so as to prevent leakage and loss of sample
 while filtration takes place. This is especially critical when low sample
 volumes are being filtered. The lock is conventional and includes outer
 annular wings designed to be removably engaged (by twisting) in
 corresponding thread-like ribs in the outlet portion of the syringe. The
 internal diameter of the female luer is standardized, according to ANSI
 specifications, to receive a corresponding standardized male luer such as
 on a syringe. This standardization ensures that the male and female
 portions will properly mate. As an alternative to the luer lock design, a
 friction fit ("luer slip") can be used, especially in low-pressure
 applications.
 Similarly, the male luer slip outlet on the syringe driven filter device
 allows, for example, a needle to be attached to the outlet of the filter
 and facilitates a direct injection of a filtered sample into an HPLC (high
 pressure liquid chromatography) instrument, for autosampler vials or other
 receptacle for further analysis.
 Another conventional syringe driven filter device is illustrated in FIG. 2.
 This device includes a narrowed outlet or "recorder taper" used in place
 of the male luer slip of the device of FIG. 1. The recorder taper is
 narrower than the male luer slip, and thus does not function as a luer
 (i.e., it does not allow for a friction-fit engagement with a standardized
 female luer). However, the recorder taper facilitates filtration into
 small receiving vessels such as HPLC autosampler vials, vial inserts and
 the wells of microtitre plates. The smaller outlet further minimizes the
 potential of the filtered sample becoming lodged ("airlocked") through
 capillary action in the top of the narrow receiving vessel such as an
 autosampler insert, as the air caught beneath the sample cannot escape to
 allow the sample to flow to the bottom of the vessel. An additional
 feature of this design is a very small downstream (internal volume after
 the membrane) volume attributed to a smaller internal diameter in the
 outlet. This can be especially important with small sample volumes.
 A still further conventional design is shown in FIG. 3. This design is a 4
 mm syringe driven filter with a "tube tip" or "tube outlet". A short tube
 is inserted into the outlet orifice of the standard male luer slip design
 in order to facilitate the filtration into a small receiving vessel.
 However, this design suffers from the drawback of having a larger
 downstream volume by virtue of the length of the tube tip, which is
 undesirable with small sample volumes.
 It therefore would be desirable to provide a filter device such as a
 syringe driven filter that includes all of the features of conventional
 devices, but does not suffer from any of their drawbacks.
 It further would be desirable to provide a filter device that has multiple
 outlet features so that a single device can serve multiple laboratory
 filtration applications, thereby reducing the number of specialized
 filters the user needs to have on hand.
 SUMMARY OF THE INVENTION
 The problems of the prior art have been overcome by the present invention,
 which provides a filter device comprising a filter housing, a filter
 disposed in the filter housing, an inlet, and an opposed outlet spaced
 from the inlet, wherein the outlet comprises an extension from the
 housing, the extension extending longitudinally in the direction of fluid
 flow and comprising at least a first section having a minimum outer
 diameter and a second section downstream from the first section and having
 a terminal end having a maximum outer diameter, the maximum diameter of
 the second section terminal end being smaller than the minimum diameter of
 the first section. In a preferred embodiment, the filter device is syringe
 driven, the inlet is a female luer section, and the first section of the
 outlet comprises a shortened male luer section.

DETAILED DESCRIPTION OF THE INVENTION
 Turning now to FIGS. 4 and 5, there is shown a 4 mm syringe drive filter
 unit 10 in accordance with one embodiment of the present invention. (Those
 skilled in the art will appreciate that the filter device of the present
 invention encompasses any device that utilizes pressure differential
 across the filter to drive the liquid therethrough, including syringes,
 pipettors and centrifuge-assisted applications, and that the syringe
 driven devices illustrated and discussed are exemplary only.) The device
 10 includes an inlet end 12 and an outlet end 14 longitudinally spaced
 from the inlet end 12 in the direction of fluid flow through the device.
 The inlet end 12 comprises an aperture or opening 30 (FIG. 6) providing
 fluid communication into the filter device housing. In a preferred
 embodiment of the present invention, the inlet end 12 comprises a female
 luer section designed in accordance with conventional ANSI specifications.
 A centrally located bore 35 is provided to allow fluid communication
 between the device 10 and another device containing the sample to be
 filtered that is to be attached to the female luer in a leakproof manner,
 such as a syringe 60 (FIG. 7). It is preferred that the female luer
 include means to effectuate a luer lock, such as outer annular protrusions
 15 which are configured to screw into corresponding thread-like ribs in a
 male luer lock of the syringe 60 or the like. The luer lock prevents both
 axial and rotational movement of the filter device 10 with respect to the
 attached device, once engaged. Alternatively, a friction or slip fit is
 often suitable, such as in connection with the terminal end of a pipette
 tip 65 as shown in FIG. 8.
 Suitably located in the housing 20 of the filter unit 10 is a filter 40.
 The choice of filters will depend upon the application and is not
 particularly limited; depth filters, microporous filters, ultrafiltration
 filters, absorptive filters and any other filters or separations media can
 be used. Preferably the filter 40 is secured in proximity to the base 21
 of the housing 20 in a conventional manner, such as thermally, adhesively,
 chemically or mechanically such as with compression. An underdrain
 structure 45 comprising one or more ports is located beneath the filter
 40, in the direction of fluid flow, to support the filter and to direct
 filtrate to flow into the internal axial bore 28 and towards the outlet 14
 of the device 10. Those skilled in the art will appreciate that the 4 mm
 version of the syringe driven filter device 10 is shown by way of example,
 and that smaller and larger devices, such as 13 mm, 25 mm and 50 mm
 filters, are within the scope of the present invention. Although in such
 larger devices the housing 20 configuration changes (e.g., can be disc
 shaped rather than cylindrical as in the 4 mm embodiment) in order to
 accommodate the larger filter, the inlet 12 portion and outlet 14 portion
 are the same.
 Optionally formed in the outer surface of the housing 20 such as near the
 base 21 are a plurality of nubs, grooves, ridges 23 or the like designed
 to assist the user in handling the filter unit 10. Alternatively, spaced
 projections, wings or surface textures could be used to provide the same
 function.
 The outlet 14 portion of the device 10 comprises an extension 50 extending
 longitudinally from the housing in the direction of fluid flow. The
 extension 50 comprises at least a first section 25 in fluid communication
 with the housing 20 through the filter and underdrain, the first section
 25 having a certain minimum outside diameter. Although the outside
 diameter of the first section 25 can vary along its length, the minimum
 outside diameter referred to herein is that portion of the section 25
 having the smallest outside diameter. The extension 50 also comprises a
 second section 26 in fluid communication with the first section 25 and
 extending in the longitudinally in the direction of fluid flow. In the
 embodiment shown, the second section 26 extends axially directly from the
 first section 25 and is contiguous thereto. The second section 26 has a
 terminal end 47 having a maximum outside diameter that is smaller than the
 minimum outside diameter of the first section 25.
 In a preferred embodiment, the first section 25 is a male luer slip portion
 tapered and dimensioned in major diameter in accordance with ANSI
 standards for a male luer, and has an internal axial bore that is
 preferably centrally located. It is shorter (in the direction of fluid
 flow) in length than conventional ANSI luers, in order to accommodate the
 second section 26 without unnecessarily increasing the downstream volume
 of the device. However, it cannot be too short or the intended luer
 connection to another device will not be secure. The present inventor has
 determined that a luer length "a" (FIG. 5) of at least about 2.7 mm,
 preferably about 3.7 mm, most preferably about 4.2 mm, is sufficient to
 ensure that the connection does not fail during typical applications.
 In the preferred embodiment shown, shoulder 27 is formed between first
 section 25 and second section 26 to define a stepped configuration. Like
 the first section 25, preferably the second section 26 is tapered so that
 it narrows in diameter towards its free terminal end 47. This taper
 assists in the molding operation during manufacture. Preferably the second
 section 26 has a length of about 3.3 mm and the free terminal end 47
 thereof a diameter of about 3.16 mm. If the second section extends too far
 in the longitudinal axial direction, an insufficient amount of the first
 section 25, when in the configuration of a male luer, may be available for
 engagement with a female luer fitting of a receptacle such as a needle,
 preventing a secure fit. The first and second sections have communicating
 internal axial bores (shown as 28), preferably centrally located, the
 diameter of which can vary in accordance with the application. The small
 outer diameter of the terminal end 47 of the second section 26 relative to
 the outer diameter of the first section 25 allows the tip of the device to
 be easily inserted in a small receptacle, such as a standard HPLC vial or
 even smaller HPLC vial insert, thereby ensuring that the sample being
 transported to that receptacle is not lost during transfer.
 In alternative embodiments, the first section 25 is barbed so as to engage
 a suitable receptacle, or is configured to form a slip fit with the inlet
 of a pipette tip 65, for example, as shown in FIG. 9. Similarly, the
 second section 26 could be barbed, or could be configured to form a slip
 fit with the inlet of a pipette tip 65 as shown in FIG. 10.
 Since the filter units of the present invention are generally disposable,
 they are preferably constructed of an inexpensive thermoplastic material
 such as a polyolefin, preferably polyethylene or polypropylene. Those
 skilled in the art will appreciate that other materials of construction
 are suitable, such as stainless steel, where the economics so allow. A
 conventional molding operation can be used to form the units, which are
 preferably one integral piece.
 Those skilled in the art will appreciate that the foregoing embodiments
 utilize generally cylindrical configurations, but that other shapes are
 within the scope of the present invention. Thus, the inlet and/or the
 first and/or second sections could have polygonal cross-section, in which
 case the limitations discussed above with respect to the dimensions of the
 outside diameters would instead apply to the outside perimeters.