JPH0457377B2 - - Google Patents

Abstract

A disposable pipette tip (10) is formed for automatic installation and removal with low friction between the tip and pipette body (16) and a predetermined distance from the pipette body end (19) and the tip intake/discharge opening (12). The tip has a conical section (11) whose small end defines the tip intake/discharge opening and a cylindrical collar (14) that receives the pipette body. The tip is formed with an internal pipette seat (17) at the junction of the conical section and cylindrical collar so that the distance between the tip inlet/discharge opening and the pipette body end is fixed. The cylindrical collar also has a circumferential sealing rib (30) axially spaced from the pipette seat to form an air seal to account for manufacturing tolerances in the tip's cylindrical portion as to both diameter and roundness while taining low friction for installation and removal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a disposable pipette for picking up and dispensing minute amounts of liquid to any desired level.

In particular, it relates to a pipette tip that is automatically picked up and ejected by a reciprocating pipette. The tip is preferably made of a moisture-resistant plastic having a conical pick-up tip section terminating at its proximal end in a generally cylindrical section that mates with the pipette cylinder. The cylindrical part is (1), the stopping part,
Preferably, the shoulder of its point of articulation with the conical tip forms a known and repeatable distance from the pipette cylinder to the level of tip intake and ejection and defines a seat for the end of the pipette cylinder. and (2) an integral inner circumferential seal between the stop and the open end of the cylinder for imposing a low friction, airtight seal around the pipette cylinder.

<Background Art> Pipettes for precisely manipulating small amounts of liquid are known in the fields of chemistry, biology, and biochemistry.
They are particularly useful for dispensing and transferring microliter quantities of culture media, diluents, and other liquids from one location to another.

Generally, such pipettes are used for wicking liquid from or dispensing liquid into test tubes or wells in microtiter trays by means of replaceable tips.
It includes a syringe with a reciprocating pump plunger acting within a cylinder. Such pipettes are usually used individually or in groups for manual operation.

An automated liquid transfer system using a pipette has recently been developed by the applicant. This system is designed specifically to avoid multiple contamination or liquid carryover.
The replaceable tip is intended for removal and treatment after each transfer of liquid from one liquid volume or sample to another. Since the entire system is applied continuously and automatically through a number of steps, each of which (1) has a presetable frictional force for easy insertion and removal of the tip and pipette end or cylinder; and (2) a predetermined mounting distance from the inlet end of the tip to the end of the pipette cylinder.

It is hitherto known to form pipette tips into a generally conical shape so that they can be replaced after each use to avoid contamination of the liquid during suction or expulsion with other liquids. For example, it is often desired to use one chip for a single purpose for liquid withdrawal and dispensing, for filling and diluting microbiological samples. Various configurations of friction and attachment between the pipette cylinder and the disposable tip have been proposed by previous workers. however,
This joint was inherently adequate to ensure a fluid-tight fit between the cylinder and the tip and to prevent accidental displacement of the tip due to fluid pressure exerted by the pump mechanism of the pipette. Furthermore, this connection does not require a predetermined spacing between the end of the pipette cylinder and the entrance/exit end of the tip. Since the pipette and tip are primarily controlled or manipulated by hand, the total friction between the tip and cylinder, either singly or as a group, is not important. Furthermore, this frictional fit is readily obtained through the use of a conical end on the pipette cylinder that has a taper that is substantially the same as the inside surface of the tip. However, even a slight deformation in the diameter of the taper between the insert and the inserted body has a large effect on the overall length of the assembly, and even a small error in the included angle can be significant at the tip of the long object. The error will be. Moreover, as noted above, the assembled length varies according to the insertion force. Therefore, automatic insertion results in significant length errors with this sealing device. Since the chip is typically molded from plastic material, small variations in taper and internal dimensions occur.

The force to remove the tip from the pipette cylinder also varies with substantially conical seals.

Although an airtight seal is a prerequisite for proper suction through the chip for automatic installation and removal, this friction must also be low and must be substantially reproducible for each replacement.

SUMMARY OF THE INVENTION The present invention is a disposable pipette tip that includes an elongated conical tube, a small diameter end of the tube that defines the passage of liquid, and a large diameter end that receives the end of a pipette, the tip being connected to the pipette end. a generally cylindrical collar for receiving a conical tube, the collar being axially aligned with the conical tube and opening into the large diameter end of the tube;
and has a stop for engaging the pipette and a circumferential seal for forming a friction fit and seal with the side wall of the pipette to establish a precisely controlled distance from the end of the pipette to the small diameter end of the pipette tip. It is characterized by the fact that

As noted, the collar stop provides a seat for the end of the pipette in order to provide a predetermined length for the entire mounted assembly; in this way, capillary action The distance between the inlet end of the tip and the liquid surface to within a few hundredths of a centimeter is mechanically controllable when the tip is picked up. Additionally, the inlet end of the tip can be precisely positioned at any desired or given level in the well of the microtiter disk, such as at the oil-water interface. The circumferential seal between the collar lumen and the pipette cylinder ensures microfriction for a positive air seal on the tip within reasonable manufacturing tolerances. The circumferential rib seal also ensures easy movement of the tips for disposal after a single use, especially when a number of pipettes are assembled together and one ejector simultaneously discards the tips from each pipette. Guarantees easy movement.

<Example> As shown in FIG. 1, a disposable pipette tip 1
0 includes an elongated hollow conical tube section 11 with its inlet and outlet ends 1 perpendicular to the axis of the conical section 11
It ends with 2. The proximal end 13 of the conical tube 11 is integral with a cylindrical mounting collar 14. As best seen in FIG. 2, the collar 14 is provided with a mounting and sealing arrangement having the end 15 of the pipette cylinder 16 supported by a mounting piece 18. As shown, the pump plunger 22 is positioned for reciprocating movement within the bore 24 of the pipette cylinder 16 for drawing in and expelling liquid from the end 12 of the tip 10.

According to the invention, the lower end 19 of the barrel end 15 seats on a shelf or collar 17 formed at the transition between the conical portion 11 and the cylindrical bore 20 of the collar 14. Edge 1
9 on the shelf 17 defines the precise distance from the mounting piece 18 to the chip inlet-outlet port 12. It is noted that radial projections other than shelves or collars may be used to define an axial stop with respect to the end of the pipette cylinder, and that the projections need not be located at the transition between the conical and cylindrical portions. It will be recognized. In this regard, the stop is defined by a rim at the mouth of the cylindrical part, which is applied to engage a radial collar or other radial member on the outside of the pipette. As illustrated by the location of the entrance/exit 12 in the recess 26 of the microtiter tray 27,
The amount of liquid in this cavity is always in a microliter. Therefore, the capillary attraction between the liquid and the top of the tip 11, especially in the vicinity of the opening 12 and the neck 26, is critical for correct control of the volume to be transferred. For this reason, the lower end 19 of the tube end onto the collar 17
The seating allows control of the length of the capillary action, as pointed out in 28, for example, where its length is known and predetermined for suitable automatic operation of the pipette. do. Moreover, in cell culture it is often desirable to be able to withdraw or dispense fluids in microtiter wells to precise standards. For example, if the cell culture is underwater below an oil layer, it is important to allow the transfer of the aqueous phase without interference of the oil phase, or vice versa.

Additionally, the present invention includes the lumen 20 of the collar 14 including an integral circumferential rib or ring 30. As shown in FIG. 3 and in an enlarged view in FIG. 5, the ribs 30 preferably have an axially deformed V-shape in cross section. This construction allows for a low-friction fit between the sidewall of the tube end 15 and the lumen 20 of the tip 10 during insertion and removal, while allowing for large manufacturing tolerances (a few thousandths of a centimeter) in the diameter of the lumen 20 and the cylinder. ). Such tolerances are especially critical in the molding of chips 10, preferably in thermoplastic or thermoset materials, such as polymers such as polypropylene, polyvinyl chloride, and fluorine carbide. At the same time, the air-tight seal between the tip and the pipette allows the aspiration of liquid through the port 12 without leakage around the end 19 of the barrel end 15 or dependence on an air seal between the collar 17 surface and the end 19. guaranteed. As an alternative to the rib 30, the inner wall of the collar may have a gentle slope which allows the pipette to form a seal with the collar side wall without interfering with the stopping action.

To enable easy attachment and detachment of the tip 10 to and from the cylindrical end 15, the upper or open end 3
2 preferably has a bell-shaped mouth terminating in a reinforced upper rim portion 32. For example, the bell mouth
Even if the tip is not in the center of the hole 31 in the figure, the tube end 1
The cylindrical portion of 5 and the inner cavity 20 are easily moved in and out of the end 19 of the cylindrical end 15 so that they are easily aligned with each other. Additionally, the rim portion 32 includes a pressing surface radially displaced from the pipette barrel end 15 that can be readily engaged by a removal member 34 on an automatic removal arm 36.

The replacement tip according to the invention, in its preferred configuration, also includes three or more, preferably four, mounting splines 37 formed integrally with the upper portion of the conical portion 11. The spline 37 is also inserted into the brim and the shelf 1
Thrust relief means are provided so that the force of the cylinder 16 seated on the tip 7 does not impose deforming stresses on the tip port 12. As illustrated, the spline 37 preferably extends from the transition ring 39 just below the collar or shelf 17 to the conical portion 11.
and each terminates one quarter or less above the conical portion to form a bearing foot for holding the chip as shown. Preferably, splined end 38
to the axis of the chip in order to hold the chip in such a vertical position when seated over a hole 31 formed in a plate, tube or box support such as 40 having a flat top. This is essentially a 90° angle. As shown, the hole 31 in the box 40 is slightly larger than the maximum diameter of the conical portion 11 at the level of the spline end 38, but small enough to prevent the spline 37 from becoming stuck in the hole 13.

It should also be noted that in this manner the spline 37 is also provided with a minimal friction area for thrust relief by the ring 39 or collar 14 being a cylindrical section. The length of spline 37 is preferably such that its lower end 38 is just above the axial center of gravity of chip 10 to prevent the chip from swinging excessively in response to horizontal acceleration. Such horizontal acceleration is important in tip displacement and high speed automatic liquid transfer by the pipette barrel end 15.
This is because when the tip is placed on the tube end 15, excessive rocking of the tip requires sufficient pause to ensure alignment.

For these techniques in the industry, especially evident in the technique of molding synthetic resin materials such as polypropylene, cylindrical parts, such as the bore 20 and the splines 37, have a draw angle of less than 2° relative to the axis. must be formed.

Likewise, the cylindrical end portion 15 typically has a small pull-out angle along its cylindrical portion to facilitate insertion and removal with respect to the bore 20 as well as to provide a seal around the ribs 30. . Because the ribs 30 can withstand radial deformations to accommodate diametric or circumferential asymmetries in the sidewalls of the cylindrical end 15, the air-tight seal resists deformations in the sidewalls of the cylindrical portion 14 or pressure between the end 19 and the collar 17. can be obtained without simply relying on.

In automatic pipetting, it is important to maintain a controlled distance from the end of the pipette tip to a known level of the microtiter well.
It is essential to draw out all the liquid from the pipette tip in the conical part 11 or to pull out the material adhering to the outer surface in order to obtain reproducibility, especially for materials floating on the surface in cell culture. To enable this function to occur in automated liquid transfer systems, the chip of the present invention is particularly useful therein.
Capillary action is utilized between the liquid and the dispensing end. This requires that the distances are both known and reproducible within a few thousandths of a centimeter. It will be clear from the following description that such precise axial distances are easily obtained without being subject to friction between the tip and the pipette cylinder as they are inserted into or removed from the pipette. At the same time, such friction between the circumferential rib 30 and the cylinder 16 makes the pump plunger 22 sufficiently effective for containing or dispensing liquid volumes in the known range of 1 microliter or less to several hundred microliters. Suitable enough to form an air seal under unfavorable conditions in order to maintain effective operation.

FIG. 6 illustrates another embodiment of the seal and seating arrangement of the present invention. As shown in cross-section, the seating collar 17 includes a plurality of shelves 47 molded into the chip 10 to form a mounting end seat for the end 19.
It is formed as. Desirably three or more shelves 47 are used in this embodiment, preferably four. As further shown, a seal between the lumen 20 and the cylindrical sidewall of the barrel end 15 can be provided by an O-ring 48 placed in a groove 49 formed in the barrel end 15. FIG. 6 also shows that the tube end 15 is formed with a slightly beveled end portion 50 which is spherical in profile. The slope of the portion 50 may alternatively be conical and the end may be slightly beveled to facilitate insertion and alignment into the chip 10 having an integrally formed sealing rib on the cylindrical end 19.

It is also clear that, if desired, an O-ring can be placed on the side wall of the bore 20 of the tip 10 to form the required low friction annular seal with the cylindrical end 15.

Although in the preferred embodiment only two circumferential sealing devices are shown, auxiliary sealing ribs of similar profile are added to the bore wall 20 or barrel end 15 to provide an overall frictional limit for the device, and It will be clear that the chip removal force is not excessive.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of a disposable pipette tip made in accordance with the present invention and supported on external splines as part of a tip supply magazine having a subdivision; FIG. 2 is a longitudinal cross-sectional view of the tip of FIG. 1 seated in the pipette cylinder or tube end, with the tip's inlet and outlet ends shown in the recesses of the microtiter tray; FIG. 3 is an enlarged longitudinal cross-sectional view of the upper end of the tip of FIGS. 1 and 2 showing the pipette tip structure of the seating shoulder, the V-shaped air sealing rib of the collar, and the outer support spline; FIG. 4 is a plan view of the chip of FIGS. 1 and 2 with the intake and discharge ends taken; FIG. 5 is a sectional view of a portion of the collar wall of the chip shown in FIGS. 1 and 2, showing an embodiment of an integral circumferential seal rib formed by a molding process. FIG. 6 is a sectional view of the tip collar and pipette tip showing the arrangement of other seals and the tube tip seating shelf. 10: Chip, 11: Conical cylinder, 12: Doorway,
14: Brim, 15: Pipette tube end, 17: Shelf for seating (shoulder), 19: Pipette lower end, 20: Inner cavity of collar, 22: Pump plunger, 30: Rib,
37: Spline.

Claims (1)

[Scope of Claims] 1. A pipette tip comprising an elongated conical barrel with a small diameter end defining a passage for a liquid and a large diameter end receiving a cylindrical end of a pipette, the tip having a general body for receiving the cylindrical end of a pipette It includes a cylindrical collar that is axially aligned and opens into the larger diameter of the conical barrel and that engages the pipette to set a precisely controlled distance from the end of the pipette barrel to the smaller diameter of the pipette tip. A disposable pipette tip characterized in that it has a mating stop and a circumferential seal for forming a friction fit and seal with a side wall of the pipette. 2. The stop is: (a) a shoulder at the point of articulation between the generally cylindrical part and the large diameter end of the conical tube; (b) one or more radial projections in the collar; or (c) the collar. A disposable pipette tip according to claim 1, characterized in that it is limited by a rim at the mouth of the pipette tip. 3. The disposable pipette tip of claim 1 or 2, wherein the circumferential seal is defined by (a) a rib or (b) a gentle taper on the inner wall of the collar. 4. The disposable pipette tip according to claim 1, 2 or 3, wherein the flange has a larger diameter than the large diameter end of the conical tube. 5. Claims 1 to 4, characterized in that the collar has a withdrawal angle of less than 2° towards its mouth and the mouth is bell-shaped for receiving a pipette.
Disposable pipette tips listed in any one of the following items. 6. The outer surface of the chip has three or more bearing splines, the splines being substantially parallel to the chip axis and terminating just above the chip's axial center of gravity. Any one of claims 1 to 5
Disposable pipette tip.