U.S. patent number 3,748,909 [Application Number 05/122,872] was granted by the patent office on 1973-07-31 for pippette.
Invention is credited to Mau H. Kuo.
United States Patent |
3,748,909 |
Kuo |
July 31, 1973 |
PIPPETTE
Abstract
A pippette in which an open ended tube is filled with or emptied
of liquid by compressing or releasing a compressible bulb sealed to
one end of the tube. The bulb includes a restrictor that diminishes
the air flow into and out of the bulb to limit the maximum rate at
which the liquid can be flowed into and out of the tube
substantially irrespective of the pressure applied to the bulb. The
filter is so mounted that it is not contacted by the fluid in the
tube.
Inventors: |
Kuo; Mau H. (Atherton, CA) |
Family
ID: |
22405330 |
Appl.
No.: |
05/122,872 |
Filed: |
March 10, 1971 |
Current U.S.
Class: |
73/864.11;
422/569; 422/922 |
Current CPC
Class: |
B01L
3/021 (20130101) |
Current International
Class: |
B01L
3/02 (20060101); G01n 001/14 (); B01l 003/02 () |
Field of
Search: |
;73/425.4P,425.6 ;23/259
;141/26,286 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3285296 |
November 1966 |
Kenzo Ishimaru et al. |
|
Primary Examiner: Queisser; Richard C.
Assistant Examiner: Corr; Denis E.
Claims
I claim:
1. Apparatus for use with a fluid storage container for varying air
pressure in the container to fill the container with fluid and to
discharge fluid therefrom at a slow, controlled rate, the apparatus
comprising: bulb means constructed of a resilient material and
having means for connecting the bulb means to the container, said
connecting means providing an interior gas storage chamber between
said bulb means and said container so that the pressure in the
chamber can be varied by compressing the bulb means and releasing
the compressed bulb means, the gas storage chamber acting as a
collector for excess fluid drawn into said container when the
compressed bulb means is released, gas flow regulating means
between the chamber and the connecting means for limiting the flow
rate of gas between the chamber and the connecting means, and means
mounting the gas flow regulating means to the bulb means at a point
sufficiently remote from the container so that contact between the
fluid and the regulating means is prevented when fluid is drawn
into the container upon the release of the compressed bulb
means.
2. Apparatus according to claim 1 including a passage between the
chamber and the connecting means, and wherein the regulating means
is mounted in the passage and includes a plurality of paths
extending from one side of the regulating means to the other side
thereof, the paths having diameters in the order of between about
0.0001 to about 0.15 millimeters.
3. Apparatus according to claim 2 wherein the paths have diameters
between about 0.0002 to about 0.02 millimeters.
4. Apparatus according to claim 1 wherein the regulating means
comprises a porous plastic disc mounted to the bulb and permitting
an air passage of no more than about 120 milliliters per square
centimeter of disc area per minute when there exists a pressure
differential between the sides of the disc of no more than about 10
pounds per square inch.
5. Apparatus according to claim 4 wherein the bulb means includes
an interior groove having a width and a depth sufficient to firmly
secure the disc to the bulb means so that substantially all air
passing between the chamber and the connection means passes through
the disc.
6. A flexible, resilient pressure applying apparatus for use on
open ended tubular containers and the like to draw relatively small
quantities of liquid into and to discharge such liquid from an open
ended tubular container at a slow, controlled rate, the apparatus
comprising a tubular member having a closed end for substantial air
tight connection with an end of the container, the member including
a bulb section defining an inner chamber communicating with one of
the open ends, the bulb section being constructed of a resiliently
deformable material so that upon compression of the bulb section
the air pressure in the chamber is increased and air flows from the
chamber to and past said one open end and upon release of the
compressed bulb section a vacuum is formed in the chamber and air
flows from the exterior of the apparatus past said one open end
into the chamber, porous means independent of the member,
separating the inner chamber from said one open end, spaced from
said one open end, and providing the only passage for air from the
inner chamber to said one open end of the container, the porous
means having a number of pores and the pores having cross sections
so that the normal, unobstructed air flow between said one open end
and the inner chamber upon a sudden compression of the bulb section
and upon the sudden release of the compressed bulb section is
extended over a prolonged period of time substantially greater than
the time period required by such normal flow, and means for firmly
securing the porous means to the member between the chamber and
said one open end to prevent dislocations of the porous means
during use whereby the controlled, metered filling and emptying of
the inner chamber with air substantially independent of the force
applied to the bulb is possible.
7. Apparatus according to claim 6 wherein the member comprises a
first part defining the chamber and an elongate, tubular second
part engageable with the first part and defining the open end,
wherein the securing means are defined by adjacent portions of the
parts that define an interior groove, and wherein the porous means
is disposed in the groove and positioned transversely with respect
to the air flow direction between the chamber and the open end.
8. Apparatus according to claim 6 wherein the porous means has a
disc shaped configuration and a periphery engaging an interior
surface of the member, and wherein the securing means comprises an
annular ring disposed on each side of the disc for positioning of
the disc between the rings.
9. A pippette for metering small quantities of liquid comprising a
tube having open ends, a manually operable bulb constructed of a
flexible material and having an interior chamber, means for
airtightly securing the bulb to the tube to thereby communicate the
chamber and an interior of the tube for subjecting the tube
interior to an elevated pressure or to a vacuum upon the
compression of the bulb or upon the release of the compressed bulb,
respectively, and a porous member secured to the bulb and
positioned so that contact between the fluid and the member upon
the release of the compressed bulb is prevented to thereby prevent
a mutual contamination of the member and the fluid, the member
having a number of pores and the pores having cross sections so
that the normal, unobstructed air flow between the tube interior
and the chamber upon a sudden compression of the bulb and upon the
sudden release of the compressed bulb is extended over a prolonged
period of time substantially greater than the time period required
by such normal flow, whereby the controlled, metered filling and
emptying of the pippette substantially independent of the force
applied to the bulb is possible.
10. A pippette according to claim 9 wherein the chamber has a
volume of between about 1.1 to about 1.7 times the volume of the
tube interior to limit the intake of a fluid volume substantially
greater than the volume of the tube and to thus prevent contact
between the fluid and the porous member mounted to the bulb.
11. A pippette according to claim 10 wherein the chamber has a
volume of between about 1.3 to about 1.5 times the volume of the
tube interior.
Description
BACKGROUND OF THE INVENTION
Pippettes, constructed of an open ended tube and a resilient,
hollow bulb secured to one end of the tube are presently in wide
use for metering small amounts of liquids. The bulbs usually have
an elongate, essentially cylindrical configuration and are
constructed of a readily deformable resilient material such as soft
rubber or plastic. They are operated by grasping the bulb and
compressing it to discharge fluid from the tube. They are filled by
compressing the bulb, inserting the free tube end in the liquid and
then releasing the bulb so that a vacuum forms inside the bulb and
draws liquid into the tubular member.
Usually, the quantities drawn into or discharged from the tube are
minute, that is in the order of a few milliliters. The tube
includes graduations so that the operator can ascertain the precise
quantity discharged or drawn into the pippette. Since the operator
holds the pippette by grasping the bulb and simultaneously operates
it by compressing the bulb, and since the quantity discharged from
or drawn into the tube is directly proportional to the air volume
displaced in the bulb, it is often difficult and requires
substantial skill to operate pippettes for the discharge of small
fluid quantities. The problem is compounded by the fact that the
primary resistance against compression comes from the bulb material
and is thus a function of the bulb material and not of the
displaced volume. Unless the same bulb is employed, it is difficult
to obtain a "feel" for the liquid quantity discharged or drawn into
the pippette. Moreover, the operator might accidentally apply
excess pressure to the bulb which immediately results in a
discharge of excess material. In instances where that discharge is
into containers holding other fluids this might be highly
undesirable since such fluids can then no longer be recovered.
In the prior art, it is known to employ various media to prevent
the accidental discharge of excess fluid described in the preceding
paragraph. Most commonly, a porous membrane or filter is placed
across the opening of the liquid storage container, e.g. the
pippette or a bottle, which permits the passage of limited
quantities of the liquid per unit time for any given pressure
applied upstream of the filter. The danger of accidental liquid
discharge at a more controlled rate is possible. However, such
prior art flow control devices are often undesirable or unusable
since they entail a contact between the liquid and the filter
material. Such contact can result in the contamination of one or
both of the filter and the liquid and becomes increasingly
undesirable as the viscosity of the liquid increases.
SUMMARY OF THE INVENTION
The present invention provides a pipette in which the quantity of
air discharged from or drawn into the interior of a fluid
containing tube of the pipette pippette controlled and takes place
at a rate which is substantially less than the rate with which such
air exchange would take place in prior art pippettes and the like.
Briefly, a pippette constructed in accordance with the invention
comprises a bulb constructed of a resilient material and airtightly
secured to an end of an elongate container such as a glass tube.
The bulb includes an interior air storage chamber which can be
emptied by compressing the bulb and filled by releasing the
resilient compressed bulb. Gas flow regulating means is disposed
between the chamber and the tube and limits the flow rate of the
gas between the chamber and the tube to prevent generally
uncontrolled rapid fluid discharges from and intakes into the
container due to relatively large gas flow rates. Contacts between
the fluid in the container and the flow regulating means in the
bulb are prevented to eliminate contamination of either or both and
to thus assure long, trouble free service of the pippette.
In the preferred embodiment of the invention, the flow regulating
means comprises a porous disc constructed of a plastic material
such as porous nylon (although other materials such as porous
cellulose, porous polyimids and the like can equally well be used),
in which the diameters of the pores fall within the range of about
0.0002 to about 0.02 millimeters. Operable porous members can have
pore sizes as small as 0.00005 millimeters to as large as 0.15
millimeters
In the preferred embodiment of the invention, the porous air flow
control member is a relatively thin disc placed between the
interior bulb chamber and the bulb end. The invention further
provides simple, relatively inexpensive means for firmly securing
the air flow control member in place so that pressure differentials
between the sides thereof cannot move it out of position and tilt
it.
A pippette constructed in accordance with the invention enables the
slow discharge of controlled quantities of fluid from the pippette
tube. Even if the operator substantially instantaneously and fully
compresses the bulb, the rate at which the fluid is discharged from
the tube remains substantially constant because such a bulb
compression merely results in a slight increase in the flow rate of
air past the air flow control member. The slow fluid discharge (or
intake) from a pippette thus requires substantially less skill than
prior art pippettes. Moreover, there are substantially no
variations in the liquid discharge from the pippette due to
variations of the rigidity and resiliency of the bulb material.
Furthermore, contaminations of the air flow control member and/or
the fluid due to a contact between the two is prevented and the
flow control member can be employed irrespective of the viscosity
of the fluids in the pippette.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary elevational view, partially in section, and
illustrates a pippette including an air flow regulator constructed
in accordance with the invention;
FIG. 2 is an enlarged, fragmentary elevational view and illustrates
the manner in which the regulator is secured to the bulb of the
pippette;
FIG. 3 is an enlarged plan view of the air flow regulator;
FIG. 4 is a fragmentary side elevational view, partially in
section, similar to FIG. 1 and illustrates another embodiment of
the invention;
FIG. 4A is a fragmentary, enlarged side elevational view similar to
FIG. 2 but illustrates the embodiment of the invention shown in
FIG. 4 in greater detail; and
FIG. 5 is a fragmentary, exploded side elevational view of the
embodiment of the invention shown in FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1 through 3, a pippette 8 constructed in
accordance with the invention comprises a cylindrically tubular
container 10 that terminates in open ends 12 and 14 and that can
hold the desired volume of a fluid. As seen in FIG. 1, end 14 is
tapered to a point of small diameter. A generally cylindrically
rigid, tubular member 18 has a first end 20 airtightly secured to
the middle body of container 10 and another end to a bulb 16 which
is constructed of a readily deformable resilient material such as
soft rubber or plastic. The bulb defines an interior space or
chamber 24 that communicates with interior space 25 of tubular
member 18 and an interior space 26 of tube 10 via a passageway
28.
Pippette 8 is used by compressing bulb 16 to evacuate air from
chamber 24 past passageway 28, interior tube space 26 and out
through open end 14 of the tube. Tapered end 14 is then immersed in
a liquid (not shown) and bulb 16 is released. The resilient nature
of the bulb material forces the bulb back into its original shape
whereby a vacuum is formed in the chamber and liquid is drawn
through tapered tube end 14 into interior space 26 until the bulb
has fully returned to its relaxed position. The liquid entering
tube 10 ascends in interior space 26 until it reaches the upper end
12 of the tube where it overflows and eventually collects in bottom
part 27 of interior space 25 of the rigid tubular member 18. An
exact, predetermined volume of liquid is now held within container
10. To prevent an excessive liquid overflow accumulation in the
interior space of tubular member 18, the bulb volume is constructed
so that it is approximately 1.1 - 1.7 times, preferably 1.3 - 1.5
times the volume of interior tube space 26. When the bulb is
manually depressed, approximately two-thirds of its volume is
evacuated therefrom so that upon its release the same two-thirds
volume is drawn into space 26. Oversizing the chamber as above
indicated allows tube 10 to be exactly filled without excessively
spilling liquid into the tubular member 18.
An air flow restrictor or regulator 30 is placed between interior
space 26 of tube 10 and chamber 24. The restrictor substantially
reduces the air flow between that space and the chamber from what
it would be if no such restrictor were provided to prevent rapid
and relatively uncontrollable liquid discharges or intakes into
tube 10. The restrictor comprises a porous, substantially circular
disc 32 which has a multiplicity of pores or paths that extend from
one side of the disc to the other. The paths are sufficiently small
so that they substantially impede the air flow therethrough. A
rapid compression of bulb 16 which correspondingly decreases the
volume of chamber 24 thus results in a pressure buildup in the
chamber instead of a substantially instantaneous large gas flow
from the chamber into the fluid holding tube 10. The pressure
buildup in the chamber results in a flow of gas through the paths
which is relatively slow and extends over an appreciable time
period. The flow can be stopped at any time by releasing the
compression of the bulb and permitting it to partially or fully
return to its original configuration. In this manner, small
quantities in the order of a fraction of one millimeter can be
discharged without taxing the operator's skills.
In a presently preferred embodiment of the invention the bulb is
secured to rigid tube section 18 that is secured to tubular
container 10 such as by interengaging end 20 of the section with an
annular protrusion 36 on the exterior of tubular container 10. The
bulb is defined by a cartridge-like insert 38 that defines chamber
24 and passageway 28 and which includes a reduced diameter axial
protrusion 40 that extends into the open end of tube section 18 and
there secured to the tube section such as by cementing it,
providing a friction fit, threading the tube sections and the axial
protrusion, and the like.
Spaced some distance towards tubular container is an inwardly
extending annular ring 42 which projects from tube section 18 and
defines an annular groove 44 into which porous disc 32 is fitted to
securely hold and position the disc and prevent its movements when
its sides are subjected to pressure differentials. A retaining ring
46 is disposed in the groove on each side of the disc and
facilitates the firmness with which the disc is grasped,
particularly when the disc lacks rigidity as when it is constructed
of a deformable material. The retaining rings further enhance the
seal between the disc periphery and the groove to assure that no
air passes from chamber 24 to tube interior 26 without passing
through the pores in disc 32.
The clamping of restrictor disc 32 between bulb 16 and tube section
18 enables a quick replacement of the disc should it become damaged
or clogged with dust particles or the like. Moreover, it provides a
convenient expedient for mounting the porous disc some distance
above the end of tubular container 10 secured to the bulb so that
even if more fluid than can be held by the container and the tube
section is drawn, and therefore spills over into the tube section,
it is prevented from contacting the restrictor and contaminating or
plugging it.
A typical construction of a pippette which has a fluid holding
capacity of about 0.2 to 5 milliliters without spilling over the
upper end of the tubular pippette container employs a bulb which
defines a compressible air chamber of a volume that is 1.1 - 1.7
times, preferably 1.3 - 1.5 times the volume of the fluid
container. The porous member that restricts the air flow between
the chamber and the tube container is so constructed that it
permits an air flow of about 0.16 to about 0.5 milliliters per
second, at an air pressure differential between the two sides of
the disc of between about 3 psi to about 10 psi. Assuming the disc
to have a total area of approximately 0.25 square centimeters, the
desired flow rate is about 40 milliliters to about 120 milliliters
per cm.sup.2 per minute. This is, for example, obtainable with a
disc constructed of porous nylon that has a thickness of about 0.1
millimeters and an average pore size of about 0.0002 millimeters.
For a disc yielding the same flow rate but constructed of a
different material, having a different thickness, and/or different
diameter pores one or more of the parameters have to be suitably
adjusted. Such adjustment in the dimensioning of the disc are
readily within the purview of those skilled in the art.
Referring to FIGS. 4 through 5, a pippette 48 constructed in
accordance with another preferred embodiment of the invention is
illustrated and comprises a tubular container 50 that is identical
to container 10 illustrated in FIG. 1 except that annular
protrusion 36 on the tube exterior is deleted. Container 50
terminates in a discharge end 52 and an open upper end 54 over
which a generally cylindrical tubular bulb 56 of uniform wall
thickness is placed. One end of the bulb is closed and the open end
is secured to upper end 54 of tube 50 by suitable means such as a
clamp (not shown), a friction fit or the like. The bulb defines an
air chamber 58 and is constructed of a readily deformable,
resilient material. Air flow restrictor 30 is incorporated by
placing porous disc 32 above upper end 54 of tube 50 against an
inwardly extending annular support 55. The disc is preferably
spaced from the upper tube ends by clamping ring 46 and another,
inner clamping ring 46 is provided on the other side of the disc to
retain the disc in the position in which all air flowing between
the chamber and the tube must pass through the pores and the disc
and to prevent the disc from falling out of the bulb when the bulb
is removed from the tube. To assure a firm connection between the
porous disc and the interior of the bulb the periphery of the disc
and of the clamping rings 46 are such that the natural resiliency
of the bulb presses against them to generate friction forces
between them. Pippette 48 illustrated in FIGS. 4 through 5 is
operated in precisely the same manner as pippette 8 illustrated in
FIGS. 1 through 3. Porous disc 32 impedes the air flow between
chamber 58 and tubular container 50 so that a slow fluid discharge
from or intake into the container can be attained irrespective of
the speed with which bulb 56 is compressed or released.
* * * * *