US 3141336 A
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United States Patent 3,141,336 PIPETTE William M. Oates, San Carlos, Calif., assignor to Beckman Instruments, Inc., a corporation of California- Filed Mar. 8, 1961, Ser. No. 94,381 Claims. (Cl. 73-4254) This invention relates generally to a pipette and more particularly to a precision pipette.
Pipettes are employed for measuring and dispensing accurate volumes of liquid. One type of pipette includes a body portion which defines the major portion of the volume to be dispensed and end portions which terminate in capillary passages. When appropriately calibrated, pipettes of this type retain an accurate volume of liquid between the meniscuses formed at the capillary ends.
One method of forming pipettes of this type is to warm predetermined regions of a thermoplastic tube and draw the tube down at these regions to form a pipette whose body portion has substantially the diameter of the original tube and whose ends are of reduced diameter. Pipettes manufactured by this method are preferably individually calibrated.
Another method of forming pipettes is to place a tube in an exterior mold and then expand the plastic into the mold. However, the final volume may not be accurate since the thickness of the material forming the walls of the pipette may vary considerably.
It is a general object of the present invention to provide an improved pipette.
It is another object of the present invention to provide a precision pipette which is easy and inexpensive to manufacture.
It is another object of the present invention to provide a pipette which can be molded around a core of predetermined volume.
It is another object of the present invention to provide a pipette which includes two portions which are secured to one another.
These and other objects and features of the invention will be more clearly understood from the following description in conjunction with the accompanying drawing.
Referring to the drawing:
FIGURE 1 shows a pipette in accordance with the present invention;
FIGURE 2 shows the mounting end of the pipette of FIGURE 1;
FIGURE 3 shows the body portion of the pipette of FIGURE 1;
FIGURE 4 shows another pipette in accordance with the invention; and
FIGURE 5 shows a typical application of pipettes in accordance with invention.
Referring to FIGURES 1 and 2, the pipette includes a mounting member 11 and a body 12. The pipette is preferably made of plastic material, such as polyethylene. The mounting member is tapered 13 for insertion into an accommodating opening. An annular groove 14 provides means for locking the mounting member 11 in the accomrnodating opening. The enlarged end 16 of the member 11 includes an internal shoulder or face 17 and a lip 18 which define an internal groove 19. The member 11 includes a small diameter or capillary passage 21.
Referring to FIGURES 1 and 3 the mounting member 11 is adapted to receive and hold the body portion 12. The body portion is generally cylindrical and has one end 23 of reduced diameter. The other end 24 includes a rim or flange 26 which is adapted to fit into the annular groove 19 of the mounting member. The face 27 of the body portion is adapted tov abut the shoulder 17 and; form a fluid tight seal; therewith. The lip 18; serves to hold the parts together and to provide an axial force which maintains the. shoulder and face in sealing relation-. ship. The body includes a passage. 28 of enlarged diameterthroughout the. major portion of its. length. The end 29 of the passage is of smaller or capillary diameter.
The pipette serves to retain liquid by the capillary faces arising at the capillary passages 21 and 29 at the ends. Relatively large amounts of liquid can be measured, however, since the passage 28 is of enlarged diameter the total amount of liquid retained in a filled pipette is determined in general by the length and diameter of the passage 28.
The pipette described is relatively easy to manufacture since the two portions can be formed on removable cores of exact volume. This simplifies production since it eliminates having to calibrate each pipette. Production is further simplified since only one size of mounting member 11 is required for a large variety of bodies 12.
Rather than making a pipette in which the body 12 is removably retained in the mounting member 11 the pipette may be formed with the body 12 permanently sealed to the mounting member 11. This is illustrated in FIGURE 4 wherein the mounting member 11 includes a face 36 adapted to be sealed to the face 37 of the body 12. In other respects the mounting member 11 and body 12 are as previously described and bear the same reference numerals.
A pipette of the above type may, for example, be used in an assembly of the type shown in FIGURE 5. The assembly includes a deformable bottle 41 provided with a dome 42 which is held by a cap 43. This pipette 44 is inserted through the accommodating opening 46 in the dome and retained by the cooperation of the groove 47 and the dome.
In use the bottle is squeezed, the end 48 of the pipette inserted in a liquid and the bottle released until the pipette is filled. Excess liquid flows into the bottle which acts as a reservoir. To dispense the accurate amount of liquid retained in the pipette the bottle is again squeezed.
1. A pipette comprising a mounting member formed to include a capillary passage and a relatively enlarged hollow portion, the interior of said capillary passage gradually diverging from one end into said enlarged hollow portion to provide a gradual interior transition therebetween, the exterior of said mounting member being formed with a relatively long conically tapered end region bounded by an annular groove, said annular groove being adapted to lock into an opening in a resilient wall of a dispensing bottle to support the end region cantilevered into the interior of said dispensing bottle, said pipette further comprising a body member formed to include a capillary passage and a relatively enlarged hollow portion, the interior of said body member gradually diverging from the inner end of the last said capillary passage into the last said enlarged portion to provide a gradual interior region of enlargement therebetween, said body member being connected to said mounting member with the interior surfaces of both said enlarged portions dimensioned and aligned to provide a smooth juncture therebetween.
2. A pipette as in claim 1 wherein said body is permanently secured to the mounting member.
3. A pipette as in claim 1 which is made of polyethylene.
4. A pipette comprising a mounting member formed to include a capillary passage and a relatively enlarged hollow portion, the interior of said capillary passage gradually diverging from one end into said enlarged 3,141,336 3 4 hollow portion to provide a gradual interior transition References Cited in the file of this patent therebetween, said pipette further comprising a body UNITED STATES PATENTS member formed to include a capillary passage and a relatively enlarged hollow portion, the interior of said body 1,204,125 Brosnan 7, 1916 member gradually diverging from the inner end of the 5 2,376,231 (3011.11 y 15, 1945 last said capillary passage into the last said enlarged 2,667,074 wlfllt'ehln eta-1 M1116, 1954 portion to provide a gradual interior enlargement there 2,702,125 Wlllmger et a1 1955 between, said body member being removably secured to 2974528 Saul Mali 14, 1961 said mounting member with the interior surfaces of both OTHER REFERENCES said enlarged portions dimensioned and aligned to pro- 10 u vide a Smooth juncture therebetweem Kllk Quantitative Ultra MICI'O Analysls, John Wiley &
5. A pipette as in claim 4 which is made of polyethylene. S0119, New York 1950 (P 24 and
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