Pipette Assembly

Abstract

A pipette assembly for accurate aspiration and discharge of fixed amounts from a pipette tip is disclosed. A spring-biased cylinder is mounted for rotation about its longitudinal axis for selecting the desired volume of liquid to be discharged. A variable volume control chamber is defined between the ID of the cylinder and the OD of a stationary piston rod. Reciprocation of the cylinder varies the volume of the control chamber.

Description

This invention is directed to a manually operable pipette assembly which is more accurate than the prior art, reduces mechanical handling during usage, and increases the efficiency in dispensing at a constant rate of discharge.

A typical example of the prior art is shown in U. S. Pat. No. 3,290,946 dated Dec. 13, 1966. When the plunger in said patent is pushed in, it is necessary to keep one's finger over the hole in the plunger. Thereafter, the plunger is permitted to reciprocate away from the pipette tip to aspirate liquid into the pipette while at all times maintaining a finger over the hole of the plunger. Thereafter, dispensing is attained by removing one's finger from the hole in the plunger. Thus, the prior art is a three-step process while relying on finger manipulation and judgment for accuracy as to the amount of liquid being dispensed.

In the present invention, the number of steps is reduced when using the pipette assembly while at the same time the operator has the ability to dispense a predetermined small amount of liquid with accuracy in excess of 99 percent. Further, the pipette assembly of the present invention is less expensive and easier to assemble than some prior art devices. While the pipette assembly has a variety of uses, it is particularly adapted for use in connection with a blood coagulation analyzer such as that disclosed in U. S. Pat. No. 3,658,480 dated Apr. 25, 1972 wherein the amount of liquid being dispensed by the pipette assembly must be accurately controlled.

It is an object of the present invention to provide a novel pipette assembly.

It is another object of the present invention to provide a pipette assembly for accurately dispensing small amounts of liquids.

It is another object of the present invention to provide a pipette assembly which is easy to assemble and requires fewer steps during usage.

It is another object of the present invention to provide a pipette assembly wherein the user may selectively choose one of several fixed amounts of liquids to be dispensed.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a perspective view of a pipette assembly in accordance with the present invention.

FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1.

FIG. 3 is a sectional view similar to FIG. 2, but illustrating the components in their relative position when the spring is compressed.

FIG. 4 is a perspective view of the adapter shown in FIG. 1, but on a larger scale.

FIG. 5 is a perspective view of the end of the adapter in FIG. 4, but on a larger scale.

FIG. 6 is a perspective view of the end of the adapter in FIG. 4, but on a larger scale.

Referring to the drawing in detail, wherein like numerals indicate like elements, there is shown a pipette assembly in accordance with the present invention designated generally as 10. The assembly 10 includes a housing 12. Housing 12 is preferably a cylinder of aluminum, but may be made of other materials and may have other cross-sections. The housing 12 has first and second ends.

The first end of the housing 12 is provided with threads on its inner periphery engaged with threads on the outer periphery of a reduced diameter portion 16 of a pipette support designated generally as 14. The pipette support 14 is in the form of a nose with a constantly reducing cross-sectional area from the diameter of the housing 12 down to the diameter of an axial barrel. The pipette support 14 is provided with an axial bore 18 therethrough and terminates at its free end in a reduced diameter portion 20. The reduced diameter portion 20 is adapted to removably receive an expendable hollow pipette tip 22. The pipette tip 22 may be a disposable pipette of high density, rigid polymeric plastic materials such as polypropylene.

The second end of the housing 12 is closed by means of an adapter 24. The adapter 24 has an end face 25 and a shoulder 26 for contact with an end of the housing 12. Threads on the ID of said second end of the housing 12 are engaged with threads on the OD of said adapter 24. It will be noted that the adapter 24 extends into the second end of the housing 12 and terminates in a reduced diameter portion 28 having an axial bore 30.

A hollow rod 32 has one end threadedly coupled to the pipette support 14. A bore 34 in the rod 32 communicates directly with the bore 18 and the interior of the pipette tip 22.

A head 36 has a reduced diameter portion telescoped into and fixedly secured to the other end of hollow rod 32 in any manner such as by a force fit. A seal 38 is supported by the head 36 and clamped against the end face of rod 32. Seal 38 will perform the function of a piston. Thus, rod 32 may be referred to as a piston rod.

A cylinder 40 is disposed within the housing 12 and surrounds a portion of the rod 32. Cylinder 40 is spaced from the outer periphery of rod 32 to define a chamber therebetween designated 46. Seal 38 engages the ID of cylinder 40 and constitutes a sealing means for one end of the chamber 46. A cap 42 is connected to the cylinder 40 in any convenient manner such as by threads. Cap 42 cooperates with a seal 44 which is clamped against an end face of the cylinder 40. Seal 44 seals the other end of chamber 46. Chamber 46 communicates with the bore 34 by means of one or more passages 48 in the rod 32. The passages 48 are in the nature of bleed holes.

The cylinder 40 is provided with a limit stop 50 which may take the form of a radially outwardly directed pin. The reduced diameter portion 28 on the adapter 24 is provided with circumferentially spaced recesses 52, 54 and 56, each adapted to selectively receive the pin 50 and thereby limit the extent of movement of the cylinder 40 in a direction away from the pipette support 14. The depth of the recesses 52, 54 and 56 is each different.

In a typical embodiment, the depth of the recess 56 is 0.742 inch and is chosen so as to result in a discharge of 0.2 ml from the pipette tIp 22. Also, the depth of recess 54 was 0.355 inch to result in a discharge of 0.1 ml from the pipette tip 22. Also, the depth of recess 52 was 0.158 inch so as to discharge 0.05 ml from the pipette tip 22. The depth of the recesses 52-56 and other related dimensions on other components may be varied as desired to effect any particular volume of discharge from the pipette tip 22.

In order that the desired volumetric discharge may be selectively attained, the assembly 10 includes a selector 58 having a reduced diameter portion telescoped into and fixedly secured to the cylinder 40 in any desired manner such as a force fit. The selector 58 is provided with a plurality of pointers 60 circumferentially disposed about the selector 58 and preferably each of a different color. Each pointer 60 may be selectively aligned with an indicator point 61 on the end face 25 of the adapter 24. Adapter 24 is provided with a stepped bearing 62 to facilitate rotational support of the casing 40 about its longitudinal axis.

The rod 32 is stationary. The cylinder 40. may rotate about its axis and is also adapted for movement in an axial direction. A spring 64 surrounds the hollow rod 32. One end of spring 64 engages a face 66 on the pipette support 14. The other end of spring 64 engages the cap 42 and biases the cylinder 40 in a direction away from the pipette support 14. In FIG. 3, the spring 64 has been compressed to its maximum extent, chamber 46 has its maximum volume, and the selector 58 has contacted the bearing 62. In FIG. 2, the spring 64 has expanded to the extent permitted by entry of the limit stop 50 into the recess 54.

The pipette assembly may be used as follows: The volume of liquid to be discharged is first selected by pushing on selector 58 until limit stop 50 is outside the recesses 52, 54 and 56. Then the selector 58 is rotated. The pointer 60 may be supplemented with numerical indicia. When the pointer 60 is aligned with an indicator 61 on the end face 25, limit stop 50 will be aligned with one of the recesses 52, 54, and 56. Then pressure on selector 58 is released so that the cylinder 40 reciprocates in an axial direction, under the bias of spring 64, until the limit stop 50 bottoms out in the selected recess. As shown in FIGS. 4-6, each of the recesses 52, 54 and 56 is generally V-shaped at least at the end face of portion 28 to make it easy for the limit stop 50 to enter its recess and take into consideration that the components are slightly misaligned.

Thereafter, the assembly 10 is held in a position so that the pipette tip 22 is immersed in the liquid. Then, the selector 58 is manually pushed until it bottoms out as shown in FIG. 3. As the selector 58 and cylinder 40 move in an axial direction, the spring 64 is compressed and the volume of chamber 46 increases by the selected amount. This creates a suction effect whereby the selected or desired amount of the liquid is aspirated into the pipette 22. Thereafter, the assembly 10 is moved to a location wherein the pipette tip 22 is juxtaposed to the desired receptacle such as a test tube. The finger pressure applied to the selector 58 may then be released permitting the spring 64 to expand and effect discharge from the pipette tip 22 into the receptacle.

As the spring 64 expands, dischrage from pipette tip 22 is at the rate of expansion of the spring 64. Discharge may be at a constant rate by using spring 64 in the form of a constant force spring. Expansion of the spring 64 decreases the volume of chamber 46 and continues until the limit stop 50 bottoms out in the selected recess 52, 54 or 56 on the reduced diameter portion 28 of the adapter 24. Since discharge of the liquid from the pipette tip 22 coincides with expansion of the spring 64, any components of the liquid are intimately mixed while being discharged and are further mixed with any liquid in the receptacle.

Since discharge is at the rate of expansion of spring 64, discharge is at a rate substantially greater than the rate of discharge under the effect of gravity. Thus, the liquid being discharged is pushed out of the end of pipette tip 22 by a column of pressurized air in rod 32 and chamber 46. Hence, discharge need not be in a downward direction. The assembly 10 has been found to have a volumetric accuracy of 99.75 percent. Such accuracy is difficult to attain with prior art devices when dealing with small volumes as described above.

The entire assembly 10, if desired, may be made from materials so that it may be sterilized. In the event of an overfill of liquid, contamination may be prevented by making the cylinder 40, hollow rod 32, and head 36 from stainless steel. The remaining elements are preferably made from non-corrosive materials such as aluminum, brass and the like.

While selection of the amount to be dispensed is preferably attained by rotating the cylinder 40 relative to adapter 24, it is within the scope of the invention te attain such selection by rotating adapter 24 relative to cylinder 40 which would be limited to axial movement.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

Claims

We claim:

1. A pipette assembly comprising a housing having first and second ends, a pipette tip support coupled to said first end of said housing, said support having a bore therethrough, a stationary hollow rod in said housing and communicating with said bore, a cylinder in said housing surrounding said rod and spaced therefrom to define a chamber of variable volume, the volume of said chamber increasing when said cylinder moves toward said pipette tip support, sealing means between said rod and cylinder for sealing the ends of said chamber, spring means biasing said cylinder away from said pipette tip support to effect a decrease in the volume of said chamber, said rod having a passage communicating with said chamber, and limit stop means for limiting the extent of movement of said cylinder in a direction away from said pipette tip support due to the bias of said spring means.

2. A pipette assembly in accordance with claim 1 wherein said limit stop means is selectively operable to limit the extent of movement of the cylinder in a direction away from the pipette support to predetermined distances.

3. A pipette assembly in accordance with claim 2 wherein said limit stop means includes an adapter supported by said housing, said adapter having a plurality of recesses of different depths, each adapted to receive the limit stop member on said cylinder.

4. A pipette assembly in accordance with claim 1 wherein said cylinder is rotatably supported by the housing for rotation about the axis of the cylinder, and means connected to the cylinder for selectively rotating the cylinder about its axis relative to the housing.

5. A pipette assembly in accordance with claim 1 wherein said spring means controls discharge at a rate defined by the rate of expansion of the spring means and greater than the rate of discharge under the effect of gravity.

6. A pipette assembly in accordance with claim 1 wherein said limit stop means includes an adapter supported by said housing, said adapter having a plurality of circumferentially spaced recesses on an end thereof, said adapter surrounding said cylinder, said cylinder having a limit stop pin adapted to enter each of said recesses, and means for selectively rotating one of said adapter and cylinder about the longitudinal axis of the cylinder.

7. A pipette assembly in accordance with claim 1 wherein said chamber surrounds said rod, a head closing said rod at the end of the rod remote from said pipette tip support, said sealing means for sealing the ends of said chamber including a piston connected to said hollow rod and a seal supported by said cylinder for movement therewith.

8. A pipette assembly comprising a support housing, a pipette tip support coupled to said housing, said support having a bore therethrough, a hollow rod in said housing and communicating with said bore, a cylinder in said housing surrounding said rod and spaced therefrom to define a chamber of variable volume, sealing means between said rod and cylinder for sealing the ends of said chamber, means defining a passage communicating said chamber with the interior of said rod, spring means biasing said cylinder away from said pipette tip support whereby discharge from said pipette tip is at the rate of expansion of the spring means, and means for selectively limiting the extent of movement of said cylinder to a plurality of predetermined distances in a direction along the longitudinal axis of said cylinder due to the bias of said spring means.

9. A pipette assembly in accordance with claim 8 wherein said last-mentioned means includes an adapter supported by said housing and having a plurality of circumferentially spaced recesses of different depths, and means for rotating said cylinder about its longitudinal axis, a limit stop member secured to said cylinder and adapted to be received in said recesses.

10. A pipette assembly in accordance with claim 8 including a pipette tip removably mounted on said pipette tip support, said sealing means including a piston connected to said rod and a seal supported by said cylinder for movement with the cylinder, said spring means including a coil spring surrounding said rod.