Filter device

A device for reducing the amount of particulate contaminant in a liquid is provided which includes a hollow elongate member having first and second openings and filter means, preferably depth filter means, positioned in the elongate member, the filter means in combination with the elongate member defining a reservoir between the filter means and the first opening. The device is intended to be used with means associated with the first opening for generating a pressure differential between the interior of the elongate member and the exterior thereof whereby a liquid containing particulate contaminant may be introduced into the reservoir in the elongate member through the second opening, particulate contaminant being trapped within the filter means and a liquid with a reduced particulate contaminant may be removed from the elongate member through the second opening.

TECHNICAL FIELD 
The present invention relates to devices for filtering 
particulate-containing fluids. More particularly, the present invention 
relates to disposable devices for reducing the amount of particulate 
contaminant in a liquid sample. 
BACKGROUND OF THE INVENTION 
Liquids subjected to analysis in some instances contain sediment or 
particulate contaminants which interfere with the qualitative and/or 
quantitive tests performed on the liquid sample. In some situations, such 
as the analysis of biological fluids, particularly body fluids such as 
urine, it may not be necessary to totally eliminate all particulate 
contaminants, but merely to reduce the amount of such contaminants to 
below the level or amount which interferes with the particular test being 
performed. Current practice accomplishes such a reduction in concentration 
of particulate contaminants with a variety of devices and associated 
techniques. Most of the devices and techniques involve drawing or passing 
the liquid sample (specimen) through a course filter which permits passage 
of purified liquid (filtrate) through the filter, the filtrate being drawn 
off from the downstream side of the device, while the particulate 
contaminant is retained on the upstream side of the filter. In some of 
these devices, the filter is discarded after transfer of the liquid 
component of the sample. With other devices used for such purposes the 
entire device is disposed of after use. 
Some of these devices have shortcomings associated with the manner in which 
the device is manipulated or liquids are transferred. For example, 
introducing a sample at an upstream side of the device and removing 
filtrate from a downstream side of the device permits several potential 
sites of leakage. Additionally, with some of the devices, additional 
pieces of apparatus are required to successfully complete the transfer of 
filtrate. Many of the devices currently employed are also difficult to 
manipulate by all but those with above average dexterity. Furthermore, 
many of the techniques and devices currently employed require multiple 
steps which increase both the amount of time spent in transferring 
material and the potential for losses and contamination occurring during 
transfer and disposal of material. 
The present invention permits facile sampling, reduces transfer problems, 
and reduces the potential for contamination of the sample while removing a 
substantial amount of particulate contaminant from the liquid, retaining 
the trapped particulate material in the device, and providing filtered 
liquid with reduced particulate concentrations. The devices perform the 
sampling of liquid specimen, separation of particulate contaminant from 
the liquid component and transfer of the substantially particulate-free 
liquid using a single piece of equipment, which is disposable, in 
essentially a single, continuous operation. 
DISCLOSURE OF INVENTION 
The present invention is directed to devices suitable for reducing the 
amount of particulate contaminant in a liquid. These devices overcome many 
of the shortcomings of the prior art in that they provide facile 
operation, reduce the potential for leakage and contamination and, in most 
instances, are intended to be disposable. 
One embodiment of the present invention includes a hollow elongate member 
having first and second openings and depth filter means positioned in the 
elongate member. The depth filter means in combination with the hollow 
elongate member defines a reservoir between the depth filter means and the 
first opening. The device is intended to be used with a means associated 
with the first opening for generating a pressure differential between the 
interior of the elongate member and the exterior thereof to introduce a 
liquid containing particulate contaminant to the reservoir in the elongate 
member through the second opening. Particulate contaminant is trapped 
within the depth filter means and a liquid with reduced particulate 
contaminant may be removed from the elongate member through the second 
opening. 
Other embodiments according to the present invention include a device 
having a hollow elongate member having at least first and second openings 
and means associated with the first opening for permitting ingress of 
liquid into the elongate member through the first opening while retarding 
egress of liquid from the elongate member through the first opening. The 
device also includes means associated with the second opening for 
permitting egress of liquid from the elongate member through the second 
opening while retarding ingress of liquid into the elongate member through 
the second opening. Also provided in the device are filter means 
positioned in the elongate member between the first and second openings. 
Other embodiments of the present invention include devices for reducing the 
particulate contaminant in a liquid which comprise a hollow elongate 
member having an opening and filter means positioned in the hollow 
elongate member which has first and second sides, the first side facing 
the opening and the second side, in combination with the internal walls of 
the hollow elongate member, defining a reservoir. Valve means are also 
provided which are associated with the filter means for permitting 
substantially unfiltered liquid to flow from the opening to the reservoir 
in a first direction and filtered liquid to flow from the reservoir 
through the filter means to the opening in a second direction.

BEST MODES OF THE INVENTION 
Each of the embodiments of the present invention, although differing in 
some features are operated in a similar manner. 
In the figures, like elements are represented by like reference numerals. 
A first embodiment of the present invention is illustrated in FIG. 1. The 
device for reducing the amount of particulate contaminant in a liquid 
sample, generally designated 10, includes a hollow member 12, typically 
having an elongated shape and having a lower open end 14 and an upper end 
16. The hollow member 12 preferably has a circular cross section and 
preferably is formed from an inert, transparent material, such as glass or 
plastic. Typically materials such as polycarbonates, polystyrene, or 
polyolefins such as polyethylene and polypropylene may be used. However, 
other cross-sectional configurations and other materials may also be used. 
The term "inert" as used herein, refers to a lack of chemical reactivity 
toward solvents which may be employed and substances present in the 
specimen, particularly in biological samples, such as bodily fluids, and 
at various pH conditions, particularly those values encountere in 
biological fluids, such as body fluids. 
Particularly preferred as the hollow or tubular member 12 is an elongated 
tube of circular cross section, having generally parallel walls and 
tapering toward the lower open end 14. Particularly preferred as the 
hollow member is a glass or plastic tube similar in shape to a laboratory 
pipette or eyedropper. 
Located in tubular member 12 near the opening 14 is a porous element 18 
which functions as a depth filter. Depth filters, useful in the present 
invention, typically comprising a body of fibrous or filamentary material, 
function by providing a body of filtering material which includes tortuous 
paths for the fluid being filtered and traps particulate material at 
various points along those tortuous paths, that is, within the depths of 
the filter medium, giving rise to the conventional descriptive name, depth 
filter, i.e., such filters provide dirt capacity by retaining dirt within 
the body of the filter medium. Thus, a depth filter differs from a surface 
filter in that particulate matter is trapped largely or exclusively by 
mechanical interactions, i.e., particles being held within pores having 
dimensions smaller than that of the particle. Depending on the materials 
from which the depth filter is formed and the substances passing through 
the filter, molecular interactions, such as Van der Waals forces, etc., 
may also contribute to particle retention. When a device is used such as 
the first embodiment of the present invention, illustrated in FIG. 1, in 
which the flow of liquid is bi-directional, that is, filtrate flows in a 
direction opposite to that of the incoming liquid sample and thereby, 
comes in contact with the first surface of the filter, it is particularly 
undesirable for the filtrate, having undergone reduction in the amount of 
particulate contaminate present, to again contact particulate material 
which may be present on the first surface of the filter material and, 
which if easily dislodged, may reenter the filtrate stream as the filtrate 
exits the device. Accordingly, a depth filter in which particles are 
trapped within internal pores is desirable for such embodiments as 
compared to a surface filter in which particulate contaminants are trapped 
on the surface. 
The choice of material to be used in a depth filter may vary with the 
particular application of the device. However, like the elongated hollow 
member 12, the filters used in the present invention may be formed from 
any material which is inert or chemically unreactive toward the liquids 
employed and substantces dissolved in the liquids. Preferred as the depth 
filtration material is a hydrophobic material. Examples of preferred 
materials include polyolefins and particularly polypropylene. Glass fibers 
may also be employed when disposed so as to provide high loft. 
Particularly preferred is a filter material comprising a web of non-woven 
polypropylene microfibers available from Pall Corporation under the 
Trademark of HDC. 
It is also preferred that the depth filter be spaced from the opening 14 so 
that the internal walls of the hollow member and a surface of the depth 
filter 18 define a first chamber or antechamber 20 at the tip of the 
hollow member. The depth filter 18 may, however, be located at the opening 
14 such that no antechamber 20 is included in the device 10. In the space 
between a second, upper opening 22 and the depth filter 18 and defined by 
the upper surface of the depth filter 18 and the walls of the hollow 
member 12, is a reservoir 24 for retaining liquid which has passed through 
the depth filter 18 as it is drawn from the container holding the liquid 
sample. 
Attached to the hollow member 12 at the opening 22 is a means for effecting 
a differential pressure between the inside and outside of the hollow 
member 12, such as an aspirator bulb or the like 26. 
The device illustrated in FIG. 1 may be operated by evacuating the hollow 
member 12, e.g., by squeezing (compressing) the aspirator bulb 26. While 
maintaining the bulb 26 in a depressed or squeezed form, the end of the 
hollow member 12 having the opening 14 is placed below the surface of a 
liquid sample and the bulb 26 released slowly in order to create a partial 
vacuum in the device 10 and draw liquid in through the opening 14. As the 
liquid fills the hollow member 12, it passes through the depth filter 18 
where particulate matter is trapped. The liquid then passes into and 
begins to fill reservoir 24. While a partial vacuum still remains within 
the device 10, that is, before the aspirator bulb 26 is completely filled 
or inflated, the device is removed from the liquid sample in order to draw 
in a small amount of air through opening 14, thereby purging the lower tip 
of the hollow member 12 and the depth filter 18 of liquid. 
The filtrate in the reservoir 24 has a substantially reduced amount of 
particulate contaminants, which contaminants are trapped within the 
interstices of the depth filter 18. To transfer the purified filtrate from 
the device 10 to a receiver, the bulb 26 is again compressed to discharge 
liquid from the hollow member 12 and evacuate the device. Use of a porous 
or microporous hydrophobic material as the depth filter is preferred 
because of the affinity of hydrophobic materials for biological substances 
which, in addition to the mechanical interaction of the particulate 
contaminants with the walls of the filter pores, assists in retention of 
the particulate contaminants. However, hydrophilic materials may be used 
in this embodiment if tests show stronger attraction for specific 
substances. 
Bi-directional flow of liquid takes place in the first, second, and fourth 
embodiments of the invention, that is, liquid, particulate-containing 
sample is drawn into the device in a first sampling and filtration step, 
and liquid is discharged in a second and opposite direction through the 
same opening 14 in a second step. In the preferred embodiment of device 
10, illustrated in FIG. 1, particulate contaminants which are removed from 
the sample in the first step are substantially completely retained by the 
depth filter 18 and prevented from returning to the purified filtrate as 
it passes through the filter in the second direction. 
A second preferred embodiment of the present invention, designated 
generally as 40, is illustrated in FIGS. 2A and 2B. Like reference 
numerals are used to designate the same or similar elements as shown in 
FIG. 1. Unlike the filter 18 used in the preferred embodiment of FIG. 1, 
the filter member 28 differs from the corresponding member of the first 
embodiment in one important respect. Notably, the filter element 28 is 
provided with at least one aperture 42 passing from a first 
liquid-contacting surface to a second liquid-contacting surface and 
providing means for fluid communication between the first chamber 20 and 
the second chamber 24. When a single aperture 42 is employed, it is placed 
preferably at the center of the filter member 28. The aperture 42 permits 
flow of particulate-containing liquid into the reservoir 24 of the hollow 
member 12 after entering the device through opening 14, as shown by the 
arrows in FIG. 2A. As will be discussed in greater detail below, aperture 
42, in communicating between the first chamber 20 and the second chamber 
24, serves as a component of a one-way valve means which permits 
substantially free ingress of liquid into the hollow member through, the 
first opening and thence to the reservoir 24 while retarding free egress 
of unfiltered liquid out of the reservoir and the hollow member through 
the first opening. Attached to the hollow member 12 at the opening 22 is a 
means for effecting a differential pressure between the inside and outside 
of the hollow member, such as an aspirator bulb or the like 26. 
The filter member 28 of the preferred embodiment illustrated in FIG. 2 is 
preferably a depth filter of the same or similar material as filter member 
18 employed in the preferred embodiment shown in FIG. 1. However, contrary 
to the embodiment in FIG. 1, filter member 28 in the embodiment shown in 
FIG. 2 may be a surface filter. 
Within the second or reservoir chamber 24, is located a movable means for 
sealing the aperture(s) 42. Preferably, the movable sealing means is a 
disc 44 formed from a material which is capable of floating in the 
particulate-containing liquid upon ingress thereof into the reservoir 24 
through the aperture(s) 42. Preferably, the movable sealing means is 
formed from a solid or microporous hydrophobic material. The dimensions of 
the movable sealing means 44 should be such that when resting on the 
filter member 28, all apertures 42 are covered by the sealing means when 
the sealing means is in contact with an internal wall of the hollow member 
and oriented such that the longest dimension of the sealing means is 
parallel to the surface of the filter member 28 which faces the reservoir 
24. Thus, when employing the preferred embodiment of the movable sealing 
means, a disc 44 having a longer dimension 44a and a shorter dimension 
44b, the disc will be oriented such that the surface 44a will be in 
contact with the surface of the filter member 28 facing the reservoir when 
the device 40 is either in an empty or discharging state. The longest 
dimension of the movable sealing means should not, however, be great 
enough to entirely cover the surface of the filter member 28 which faces 
the reservoir 24. That is, the longest dimension of the movable sealing 
means, such as 44a of disc 44, should be less than the diameter of the 
hollow member. In a particularly preferred embodiment in which the hollow 
portion of the hollow member has a circular cross section, and disc 44 is 
circular, the diameter of disc 44 should be smaller than the internal 
diameter of the hollow member 12 such that, when the disc 44 is located at 
the center of the hollow member and in contact with filter member 28, an 
annular surface of the filter member 28 is exposed. 
To prevent the movable sealing means from being disturbed while filling and 
coming to rest on a shorter dimension, such as 44b, when liquid is being 
discharged from the device 40, and thereby defeating the sealing function, 
a retaining means 46 is provided in the second chamber 24 spaced from the 
surface of the filter member facing the second chamber by a distance which 
is less than the longest dimension of the movable sealing means. Thus, as 
illustrated in FIG. 2, the distance between the retaining means 46 and the 
surface of the filter member 28 facing the second chamber 24, designated 
as "x", should be less than the longest length of the surface 44a. In this 
manner, the retaining means assists proper sealing in a discharge mode and 
prevents the sealing disc 44 from turning over completely or resting on a 
side surface 44b. In addition, the retaining means prevents loss of the 
movable sealing means when a partial vacuum is created in the hollow 
member 12 upon release of the aspirator bulb 26. 
The retaining means may be of any suitable material which is inert toward 
the liquid and substances reaching the reservoir chamber 24. The retaining 
means 46 may be of any construction which permits unrestricted flow of 
liquids within the reservoir 24. Thus, the retaining means 46 may be a 
screen such as an open wire mesh of an inert material, such as stainless 
steel wire, plastic, or the like. 
The preferred embodiment illustrated in FIGS. 2A and 2B is operated in 
essentially the same manner as the device illustrated in FIG. 1. Thus, 
aspirator bulb 26 is compressed to evacuate air from the device 40. While 
maintaining the aspirator bulb in a compressed state, the tip of device 40 
is placed in a liquid sample such that opening 14 is below the surface of 
the liquid sample. The bulb is slowly released and liquid enters the 
device in the direction shown by the arrows in FIG. 2A as a result of the 
difference in pressure between the interior of the hollow member 12 and 
the outside. The particulate-containing liquid entering the hollow member 
12 passes through the opening 14 into the first chamber 20 and then 
through the aperture(s) 42. As liquid passes through apertures(s) 42, the 
movable sealing means 44 rises off its seat on top of the filter member 
28. The incoming liquid, containing substantially the same concentration 
of particulate contaminant as the liquid entering opening 14 rises within 
the reservoir 24. The disc 44 which floats in the incoming particulate 
containing liquid is prevented from rising beyond a distance x by the 
retaining member 46. When a suitable volume of particulate-containing 
liquid has filled the reservoir 24 and while the aspirator bulb is still 
somewhat compressed, the tip of device 40 is preferably removed from the 
liquid sample while continuing to release the aspirator bulb. This, as in 
the operation of the device 10 illustrated in FIG. 1, purges remaining 
liquid from chamber 20 and the filter member 28, primarily aperture(s) 42. 
At this stage in the operation of the device 40, the 
particulate-containing liquid in the reservoir 24 has substantially the 
same concentration of particulate contaminants as the originally liquid 
sample. Only very small amounts of particulate contaminant are removed 
when the incoming liquid contacts the surface of the aperture(s) 42 or the 
surface of the filter member 28 facing opening 14. 
The liquid contained in reservoir 24 is discharged from the device in a 
second step which effects removal of particulate contaminant. That is, 
aspirator bulb 26 is again compressed increasing the pressure over the 
column of liquid in the reservoir and creating a pressure differential 
between the hollow member 12 and the exterior of the device. This forces 
disc 44 into contact with filter member 28 sealing off aperture(s) 42. 
Since disc 44 is smaller than the side of filter member 28 facing the 
reservoir, liquid passes through the exposed portion of the filter member 
28 and, in doing so, filters the discharging liquid, retaining particulate 
contaminants on (in the case of a surface filter) or in (in the case of a 
depth filter) the filter member 28. Thus, the preferred embodiments of the 
present invention illustrated in FIGS. 1 and 2A and 2B operate in the 
similar manner in that both involves a two-step procedure and a 
bi-directional flow of liquid through the same opening 14. However, the 
device illustrated in FIG. 1 accomplishes filtration primarily in the 
filling step as liquid enters reservoir 24; whereas, the device 
illustrated in FIGS. 2A and B accomplish filtration as liquid is 
discharged from the reservoir through filter member 28. 
The third preferred embodiment will be better understood by reference to 
FIGS. 3A and 3B which illustrate a preferred embodiment at different 
stages of use. In FIGS. 3A and B where like members are correspondingly 
identified, a preferred device according to the present invention is 
designated generally by 30. A hollow elongate member 12 is provided having 
a first opening 31 with a check valve 32, preferably in the form of two 
flexible members 33 and 34. Flexible members 33 and 34 are resiliently 
biased toward each other to allow ingress of fluid into the elongate 
hollow member 12, when the first opening is below the surface of a liquid 
sample, as shown in FIG. 3A, by opening in response to a differential 
pressure between the interior and exterior elongate member 12, e.g., by 
pressure applied from the exterior or by virtue of a vacuum drawn on the 
interior of elongate member by the aspirator 26 (bulb). When the pressure 
in the interior of the elongate hollow member 12 is substantially equal to 
that on the exterior thereof, fluid flow into the elongate member 12 
ceases and the check valve 32 closes, retarding egress of liquid out of 
the elongate member 12 through the opening 31. 
Under the effect of a positive pressure differential between the interior 
of elongate member 12 and the exterior environment, produced, e.g., by 
squeezing the bulb 26 to increase the pressure within elongate member 12, 
check valve 36 preferably constructed similarly to the check valve 32, 
i.e., from two resilient members biased toward each other under normal 
conditions, opens allowing liquid to pass out of elongate member 12 
through opening 14. Filter means 38 positioned within the elongate member 
12 between the openings 31 and 14, preferably just above the check valve 
36, acts to removes particulate contained in the liquid as it passes 
through the filter means thereby providing a liquid with a reduced amount 
of articulate contaminant therein. 
A fourth embodiment of the present invention, illustrated in FIGS. 4A and 
B, generally designated as 50, employs, like the preferred embodiments of 
FIGS. 1 and 2, a hollow member 12. Located proximate opening 14, at one 
end of the hollow member, is a filter member 48 which is preferably a 
hydrophobic conically-shaped depth filter. The depth filter is preferably 
formed from a disc of a depth filter material, such as that used in device 
10 shown in FIG. 1. When the hollow member has the preferred circular 
cross section, disc 48 is a circular disc having a diameter larger than 
the internal diameter of hollow member 12, preferably on the order of 
about twice the diameter of the internal diameter of the hollow member. In 
a preferred embodiment in which the opening 14, formed in an end of the 
hollow member 12, has a tapered configuration, one or more tools is used 
to locate filter member 48 in the tapered portion of the hollow member and 
form a cone in which a peripheral edge 54 of the disc is formed in close 
and intimate contact with the internal wall of hollow member 12. 
To assure proper location of the filter member 48 within device 50 and 
retention thereat, a filter member retention means 52 is employed. In a 
preferred embodiment, the filter member retention means comprises a piece 
of wire which is chemically inert toward particulate-containing liquids 
and substances commonly found therein with which the devices of the 
present invention may be used. The preferred filter member retaining means 
52 has the general shape of a V, the apex of which engages the concave 
upward portion of the filter member 48. The ends of the wire retaining 
member 52 engage the side wall(s) of the hollow member in a region of the 
reservoir close to the aspirator bulb 26. Preferably the wire from which 
the retaining member 52 is formed has spring characteristics which 
provides positive engagement against the side wall(s) of the hollow member 
due to the biasing effect of the ends of the element 52 against the 
internal side wall(s) of the hollow member 12. 
The device 50 is operated in a manner similar to the preferred embodiments 
previously discussed. That is, in a first step, the aspirator 26 is 
compressed to exhaust air from the device. The tip of the device is placed 
in a liquid sample such that opening 14 is completely below the surface of 
the liquid. The aspirator bulb is slowly released and liquid enters device 
50 through opening 14 in the direction of the arrows shown in FIG. 4A. 
Thus, incoming liquid passes, to a small extent, through some of the pores 
of the hydrophobic depth filter member 50. However, with the filter member 
retaining means 52 contacting and locating the filter member 48 
substantially at the center concave portion of the filter member, the 
force of the incoming liquid forces the peripheral edge 54 of the filter 
member 48 away from the internal surface of the hollow member 12. Thus, 
the conically-shaped filter member 48, in conjunction with the filter 
member retaining means 52 and the tapered portion of the internal wall(s) 
of the hollow member functions as a self-valving one-way valve with the 
peripheral edge 54 of the filter member 48 moving away from the valve seat 
or tapered portion of the hollow member 12 in the path of liquid flowing 
into the device. 
After a sufficient volume of liquid has entered the reservoir portion of 
the device 50 and preferably a small amount of air has been admitted to 
purge the opening 14 and the filter member 48, the aspirator bulb 26 is 
compressed to discharge liquid from the device. Discharging, the liquid 
forces the peripheral edge 54 of the filter member 48 against the internal 
wall(s) of the hollow member 12, as shown in FIG. 4B. As indicated by the 
arrows therein, substantially all of the liquid passes through the pores 
of the hydrophobic depth filter 48. The device 50 removes particulate 
contaminant in part in the ingress or filling step as part of the liquid 
passes through depth filter member 48, but a major portion of particulate 
is removed in the egress or discharge step in which the only path open to 
discharging liquid is through the filter member 48. 
While the invention has been described with regard to specific embodiments, 
it should be understood that various changes and modifications can be made 
in the details of the procedure, without departing from the scope and 
spirit of the invention; therefore, it is not intended to be limited 
except as indicated in the appended claims. For example, rather than using 
an aspirator bulb to create a pressure differential between the interior 
of the elongate member and the outside, a flexible, hollow elongate member 
can be used which, upon compression (or subsequent expansion to its 
original shape), creates a pressure differential. Similarly, while the 
hollow member is described as elongated, the relative length to width is 
premarily simply determined by the ease of handling.