Abstract

Precision liquid pipetting devices for use with disposable pipettes having improved means for adjusting the stroke of the plunger within the pipette and for precisely calibrating the volumetric capacity.

Description

This invention relates generally to precision liquid pipetting devices and more particularly to improved means for adjusting the stroke of and calibrating the capacity of pipetting dispensers.

The principal object of this invention is to provide improved means for calibrating the volumetric capacity of a pipetting dispenser with a reproducible high degree of accuracy.

Another object of this invention is to provide simple means for selectively varying the volume of liquid dispensable from a micropipette of a particular size.

Other objects and advantages of the invention will become apparent upon consideration of the following description and the accompanying drawings wherein

FIG. 1 is an overall view of one embodiment of precision pipetting device employing a disposable pipette of relatively large diameter;

FIG. 2 illustrates another embodiment of precision pipetting device which employs a disposable micropipette of much smaller diameter;

FIG. 3 is a cross-sectional view of the barrel and plunger assembly of the pipetting device of FIG. 1;

FIG. 4 is a cross-sectional view of the end of the barrel of the pipetting device of FIG. 3 with a different end cap in place;

FIG. 5 is an end view of the cap ends of the pipetting devices of FIGS. 1 and 2;

FIG. 6 is a cross-sectional view of the calibration assembly of the pipetting device of FIG. 2;

FIG. 7 is a cross-sectional view of an alternate end construction for the pipetting device of FIG. 2; and

FIG. 8 is a cross-sectional view of the calibration assembly of the pipetting device of FIG. 1.

This invention relates to improvements in precision pipetting devices of the type generally disclosed in M. E. Drummond, et al. U.S. Pat. No. 3,606,086 issued Sept. 20, 1971 for Microdispensing Device. The devices include an elongated barrel 1 and a disposable pipette demountably mounted on the barrel, such as the extruded plastic pipette 2 of relatively large diameter illustrated in FIG. 1 or the smaller precision glass micropipette 2' illustrated in FIG. 2. A reciprocable plunger 3 carried in part within the barrel 1 has one end within the pipette to draw liquid into and to dispense liquid from it.

Each of the described embodiments of barrel 1 has an interior bore into which the plunger 3 passes and is affixed to a plunger holder 4 at one end. The coil spring means 5 within the bore of the barrel seats at one end against the barrel itself and at the other end against a seat 6 on the plunger holder, for example, to bias the plunger toward the withdrawn end of its stroke as is shown in FIGS. 3 and 4.

A series of end caps 7, 7', or more, each thread into the open end of the barrel and each has a bore through which the plunger holder 4 slides. These threaded end caps 7, 7' have a generally circular head 8 substantially larger in diameter than the barrel 1 which is flattened as at face 9 shown in FIG. 5 to prevent roll of the pipetting device when it is resting upon a generally horizontal surface. Each end cap 7, 7' also has a shoulder 10 spaced from its threads toward the coil spring means against which the plunger holder seat 6 abuts as the spring means biases the plunger toward the withdrawn end of its stroke. As will be noted by a comparison of FIGS. 3 and 4 the shoulder 10 of each of the series of end caps 7, 7', etc. is spaced a different difference from its threads so that by interchanging end caps one can selectively adjust the length of the plunger stroke in predetermined increments. A button head 11 threads into the remote end of the plunger holder 4 for manipulation of it. The thumb or forefinger of the user presses upon this button head and simultaneously pulls against the head 8 of end cap 7, 7', etc. to extend the plunger 3. The bias coil spring means 5 returns the plunger 3 to the withdrawn end of its stroke.

The embodiment of dispenser illustrated in FIG. 1 includes a plunger 3 which carries at its free end a semi-resilient tip 15 which is substantially larger in diameter than the plunger and flexibly embraces the interior walls of the pipette 2 to force fluid from or draw fluid into the pipette. A similar construction is shown in FIG. 6 in the tip 15' of the other embodiment of the invention. The precision micropipette 2' can be formed with an internal diameter so precise that for small diameters the plunger 3 may be deployed within it without any tip 15' as is shown in FIG. 7.

The device of FIG. 1 has a pipette stop 20 mounted adjacent to the pipette-end of the barrel which is adjustably positionable along the axis of travel of the plunger. In that embodiment the pipette stop 20 as shown in FIG. 8 comprises a hub 21 with an interior bore 22 which slides upon a cylindrical tip 23 of substantially the same diameter which protrudes from that end of the barrel 1 and sleeves over reciprocable plunger 3. Set screw 24 in the hub 21 of the pipette stop 20 can be tightened against cylindrical tip 23 to position the stop 20 at any point along it. A smaller diameter sleeve portion 25 of the stop 20 carries the flanged end of plastic pipette 2 press fit upon it with its flange 26 seated against hub 21. By precisely positioning stop 20 on the protruding cylindrical tip 22 of the barrel, one can precisely calibrate the volume of the pipette into which liquid is drawn and from which it is dispensed for any particular plunger stroke.

The structure of the dispenser embodiment of FIG. 2 is similar in function. As is illustrated more particularly in FIG. 6 the pipette stop 20' has a bore for the plunger 3 which is smaller than the diameter of the pipette 2' that mounts at the end of the barrel. The stop 20', too, is adjustably positionable along the axis of travel of the plunger 3 by shifting its position within a cylindrical bore 28 in the end of barrel 1 and by holding it there with set screw 24'. The pipette 2' seats against the pipette stop 20' and is held against it by a knurled collet 30 having female threads which thread upon a male threaded portion 31 of the barrel 1. A conical seat 32 within the threaded portion 31 of the barrel and next to bore 28 diverges outwardly toward the collet. A semi-resilient truncated generally conical pipette retainer 33 encompasses the pipette and is forced against the conical seat 32 as the collet 30 threads upon the threaded portion 31 of the barrel.

The precision pipetting dispensers of this invention provide the user with a means for precisely measuring and dispensing volumes in the order from 1 to 100 lambda or larger. They also provide a given dispenser with a variety of stroke lengths by an appropriate series of interchangeable end caps 7, 7', etc. Accuracy and reproducibility in the order of .+-.1 percent is easily attained. The dispenser is easily calibrated by placing in either of pipettes 2 or 2' a calibration tool which is nothing more than a wire or rod of predetermined length, loosening the set screws 24, 24' and in the embodiment of FIG. 2 loosening collet 30 also. With the calibration tool of known length slipped into the open end of the pipette, the pipette is placed vertically with that end against a flat horizontal surface so that the end of the tool aligns precisely with the end of the pipette. This automatically positions the loosened pipette stop for correct calibration for that particular calibration tool. The set screw 24, 24' is then tightened in this position and, in the embodiment of FIG. 2, the collet is tightened to hold the pipette against the stop 20'. The press fit of pipette 2 upon sleeve portion 25 of the stop 20 in the embodiment of FIG. 1 holds that pipette in place against hub 21 of the stop.

The two embodiments of this invention have been described for illustrative purposes only. The invention is defined in the following claims.

Claims

We claim:

1. In a precision liquid pipetting device having an elongated barrel,

a pipette mounted upon one end of the barrel, and

a plunger carried in part within the barrel and reciprocable with a predetermined stroke within the pipette to draw liquid into and to dispense liquid from the pipette,

the improvement comprising

a pipette calibration stop mounted adjacent said end of the barrel and being adjustably positionable along the axis of travel of the plunger, such that the pipette can be adjustably positioned with respect to the stroke of said plunger, and

means holding the pipette against the pipette stop.

2. The precision liquid pipetting device of claim 1 wherein the improvement further comprises a semi-resilient tip on the end of the plunger flexibly embracing the interior walls of the pipette.

3. The precision liquid pipetting device of claim 1 wherein the means holding the pipette against the pipette stop is a cylindrical sleeve integral with the stop upon which the pipette press fits.

4. The precision liquid pipetting device of claim 1 wherein the means holding the pipette against the pipette stop is a collet threaded to said end of the barrel.

5. The precision liquid pipetting device of claim 4 wherein the improvement further comprises

a semi-resilient truncated conical pipette retainer encompassing the pipette;

a male threaded portion on said end of the barrel and a conical seat within the threaded portion that diverges toward said end; and

corresponding female threads on the collet for forcing the retainer against the seat when threaded upon the male threads to retain the pipette against the pipette stop.

6. In a precision liquid pipetting device having an elongated barrel,

a pipette mounted upon one end of the barrel,

a plunger carried in part within the barrel and reciprocable with a predetermined stroke within the pipette to draw liquid into and to dispense liquid from the pipette, and

coil spring means within the barrel for normally biasing the plunger to a withdrawn end of its stroke, the improvement comprising

a pipette calibration stop mounted adjacent said end of the barrel and being adjustably positionable along the axis of travel of the plunger such that the pipette can be adjustably positioned with respect to the stroke of said plunger;

means holding the pipette against the pipette stop; and

one of a series of end caps threaded to the barrel at its other end, each of the series having a shoulder spaced a different distance toward the spring means and by abuttment selectively limiting the travel of the plunger at the withdrawn end of its stroke.

7. The precision liquid pipetting device of claim 6 wherein the end cap is generally circular with a diameter greater than the barrel and has a flattened face for preventing roll of the pipetting device when resting upon a generally horizontal surface.