MXPA01004565A - Pipette with improved pipette tip and mounting shaft - Google Patents

Abstract

An air displacement pipette (10) having axially spaced annular sealing and substantially cylindrical lateral support zones (36, 38) and regions (46, 48) on the pipette's mounting shaft and tip, respectively, in combination with means (52) for insuring uniform depth of mounting shaft penetration into the pipette tip to maintain uniform tip interference with the mounting shaft as successive tips are mounted on and ejected from the mounting shaft whereby the pipette tip is easily and firmly mountable on and easily ejectable from the pipette tip mounting shaft by the application of axial mounting and ejection forces of about two pounds and one pound, respectively.

Description

PIPETTE WITH IMPROVED COMBINATION OF PIPETTE TIP AND MOUNTING AXLE Related Application This application is partially the continuation of U.S. patent application serial number 09 / 188,032, filed on November 6, 1998, assigned to the same assignee of the present patent application.

FIELD OF THE INVENTION The present invention relates to improvements in pipettes and, more particularly, to air displacement pipettes comprising a novel mounting axis and a pipette tip unique to the measurement of the mounting axis, so that the user of the pipette can easily insert the tip of the pipette into the mounting shaft in a fluid-tight position in which the tip is secured against lateral oscillatory movement or unwanted displacement from the axis and, after of its use, the user of the pipette ejects it easily from the axis; such insertion and expulsion that the user requires only to apply the forces of insertion and expulsion of the axial tip of approximately one pound or less avoiding in its entirety that the user of the pipette suffers some injury due to repetitive movement.

It is very common to use pipette devices for the transfer and supply of precise quantities of fluids in analysis systems, as well as the use of disposable tip parts for such pipettes. Disposable tips accommodate the serial use of such pipette devices in the transfer of different fluids without contaminants.

Generally speaking, the disposable pipette tips are made of plastic and have a hollow, elongated and usually conical shape with an open proximal end to reliably receive and match the distal end of an elongated pipette tip mounting shaft and typically tapered of a pipette device. Ideally, the disposable tip could easily slide on the mounting shaft to an axial position adjacent to a lower end of a tip ejection mechanism of the pipetting device.

In order to meet the recommended sealing criteria for disposable pipette tips relative to the tip mounting axes, the inner surface and the side walls of the proximal parts of most pipette tips are axially tapered in a end to end and a half-degree angle larger than the distal end of the pipette tip mounting shaft and forms an annularly frustoconical annular sealing band. The sealing band is dimensioned to stretch outward ("circumferential stretch") when the distal end of the mounting shaft of the normally conical elongate pipette tip is forced towards the proximal end of the tip to firmly seat the tip on the shaft and creating an elongated annular seal with respect to the fluids between the sealing band and the mounting shaft. Other pipette tips, such as those described in U.S. Patents 4,748,859 and 4,824,641, comprise a plurality of annularly understandable annular sealing collars on an inner surface of the proximal end portion of such tips. The washers between the outer surface of the pipette mounting shaft and the inner surface of the proximal end portion of the tip by virtue of which the axially spaced collars are laterally stabilized against unwanted oscillatory movements of the shaft during the explosion. Usually, during the installation a pipette tip on a pipette mounting shaft, the user, applying a force down between 12 and 15 pounds, directs the mounting shaft axially towards the tip, distance from agreement with the user is sufficient to create (i) an airtight seal with respect to the fluids between the tip and (ii) the desired lateral stability for the tip with respect to the axis. On one occasion, in a wrong attempt to improve the lateral stability of a pipette tip with respect to a mounting axis, the user will apply sufficient downward insertion force (eg 18 to 25 pounds) to the shaft to axially bring the tip to the shaft to the point where a top surface of the tip engages or wedges into the arm or Ejector cone of the ejector mechanism of pipette tips. However, the contact between a lower surface of the arm or tip ejector cone and the upper surface of the tip only provides a minimum resistance to the oscillatory movement of the tip with respect to the axis and therefore all that is achieved is a minimum increase in the lateral stability of the tip on the shaft. In addition, since most pipette tips are made of relatively rigid plastic, it is difficult to achieve the necessary annular stretch of the pipette tip to accommodate the movement of the tip within the shaft especially at the point where it is engaged. the lower surface of the ejector or cone of the tip. In fact, the axial forces which must be applied on a conventional pipette to achieve such positioning of the tip on the pipette tip mounting axis exceeds twenty pounds, which is difficult for users of the pipette tip to generate. Of course, in the case of most pipette tip designs, the highest axial force exerted in the seating of a pipette tip on the pipette mounting shaft, the highest force required to eject the tip from the assembly axis. Therefore, while inserting a pipette tip into a mounting shaft until it reaches a position against a lower surface of a pipette tip ejection mechanism provides a minimal increase in lateral stability of the tip in the shaft, works against design criteria for disposable pipette tips that are easy to remove from the shaft when you want to replace the tip.

In fact, it is easier to meet the design criteria for disposable pipette tips which enjoy a stable installation and form an airtight seal with respect to fluids with a pipette mounting shaft that design criteria to slide with ease Disposable pipette tips on a pipette tip mounting shaft at an axial location form an airtight seal against fluids, being very easy to remove from the mounting shaft when you want to replace the tip.

In this regard, the pipette tip mounting shafts of the devices for transferring liquid volumes in different ranges have different external shapes. For example, it is common for the distal end of standardized pipette tip mounting shafts to transfer liquids in volumes greater than 500 microliters (large volume pipettes) to have an axial taper descending and entering approximately one degree, one degree and medium to two degrees per side from the longitudinal axis of the mounting shaft. On the one hand, the distal end of the mounting axes for the pipette devices of moderate or relatively low volume (250 microliters or less) usually have a downward and inward taper of approximately two to five degrees per side from the axis longitudinal of the mounting shaft so that the nose of the shaft will strike the inner wall of the pipette tip and cause a circumferential stretching of the same before the side of the shaft engages with the inner wall of the tip. Therefore, while the design criteria that a large-volume pipette is easy to install and remove from the assembly axis of a mounting spindle of a large-volume pipetting device can be achieved by including a portion of the proximal end with a sidewall of reduced thickness as in the large volume pipette tip disclosed in U.S. Patent 5,779,984, issued July 14, 1998, such thin-walled design will not result in a pipette tip that meets the criteria of installation design and easy ejection of pipette tips of moderate and minor volume that must be firmly installed on the mounting axes of the pipette tip with an entry point of two degrees and more. The same applies to the pipette tip design described in US Pat. No. 4,072,330 which includes a frustoconical sealing region with a thin side wall. As already mentioned, the pipette tips of minor and moderate volume comprise a band or internal surface of frustoconical annular seal with a tapered distal end of a pipette tip mounting shaft. The angle of sharpening of the sealing surface commonly approximates (e.g., one degree and one and a half degrees more than) that of the mounting axis (e.g., two to five degrees). The reduction to the thickness of the side wall of the standard and minor volume pipette tips in the region of said sealing band means an insignificant decrease in the installation and ejection forces necessary to move said tip to a sealing location and Then eject the pipette tip from the mounting shaft. In forming the desired annular seal, the frusto-conical annular region is required to stretch out as a normal ring-out (circumferential stretch) species outwardly for the tilt-fit surface of the pipette tip mounting shaft. The higher reaction forces in the tip material resist said circumferential stretching and require the use of larger axial forces (for example ten or more pounds) on the tip for the purpose of installing the tip on the mounting shaft and creating the necessary hermetic ring seal with respect to fluids. Such reaction forces increase when the tip is brought to the tip ejector mechanism of the associated pipette device. In addition, it is common for disposable pipette tips to be installed and stored on lecterns that can be sterilized. Usually, such lecterns comprise a support tray with a network of holes for receiving the distal ends of the pipette tips to orient them vertically in a separate rectilinear pattern with open proximal ends of the exposed tips to receive the mounting shafts of a pipette device in which the pipette tips are to be installed. For example, to install the disposable pipette tips contained in a tip stand on the axes of a multi-channel pipette, the pipette device is placed on the stand with its several mounting axes aligned with the open proximal ends of a series. Pipette tip dress After a slight initial insertion of the mounting shafts into the open proximal ends of the aligned pipette tips, a large downward force is exerted on the pipette device to bring the mounting shafts into the tip portions. Consequently, the pipette tips are placed firmly on the mounting axes and are lifted from the stand with upward movement of the multi-channel pipette. However, in practice, such multiple pipette tip mounting procedures often result in certain pipette tips being installed at different axial locations on certain mounting axes. In an attempt to eliminate such non-uniform mounting of pipette tips on the various channels of a multi-channel pipette, users often oscillate the pipette when the axial forces of approximately 12 to 13 pounds per channel lead to the mounting axes. the tips held by a pipette tip stand to guide the tips towards the bottom surface of the pipette tips ejector mechanism.

Moreover, the more firmly installed tip is installed or taper on the mounting axis of the pipette device, the larger axial force that the pipette user can generate by the action of his thumb and hand to eject the tip from the shaft when you want to replace a tip. In practice, it is common for the thumb and hand of the user of the pipette to generate axial forces of approximately 10 pounds per pipette channel when carrying the tip from a mounting axis. In the course of several repetitive ejection operations, especially in the case of multi-channel pipettes, which require extremely important forces to be generated, it is physically stressful for the thumb and hand of the user causing repetitive stress injuries to the thumb and the hand and in extreme cases, caused the carpal tunnel syndrome.

Likewise, standardized pipette tips as well as those described in US Pat. No. 4,072,330 are uniquely dependent on the sealing region of the pipette tip both to create the annular seal in relation to fluids and to provide mounting stable lateral tip for the shaft sufficient to resist oscillatory movement during the explosion. The structure of such pipette tips does not provide such lateral mounting stability and yet for those rare occasions in which the tips are inserted upwardly relative to the lower part of the arm or ejector cone of the pipette tip, the minimal lateral stability of the tip on the shaft.

In an effort to improve the lateral stability and retention of pipette tips on the mounting axes of certain pipettes, some manufacturers place O-type washers on the pipette mounting axes of their pipettes. For example, Brinkmann Instrument Co. notes that for its Transferpipette 8/12 such O-type washer ensures that all tips remain in place during use. However, such O-type washers exhibit rapid wear due to the repetitive insertion of the associated mounting shafts within such axes as well as the ejection of the pipette tips from such shafts. Due to wear, the tips do not remain firmly installed during use and the wear particles of the O-type washers can contaminate the fluid samples handled by the associated pipettes.

In an attempt to reduce the forces of the hand and finger that the user of the pipette must generate to eject a tip from the mounting shaft of a pipette, other pipette manufacturers such as LabSystems have developed and included in some of their pipettes gear and ratchet to amplify the forces generated by the user to eject the pipette tips from their mounting axes. Unfortunately, such mechanisms are very expensive and increase the size and weight of pipettes, which is not highly recommended.

Recently, to satisfy the ideal characteristics and criteria described above for a pipette tip, an improved plastic pipette tip has been developed which can be installed on the standardized pipette mounting shaft of the air displacement pipette and to eject from it by means of the application of an axial mounting force of less than six pounds and an axial ejection force of only three pounds. The improved pipette tip is described in the current United States patent application serial number 09 / 188,030 and entitled "Easy ejecting pipette tip". As described therein, to satisfy the mounting capacity and ease of disposal criteria for disposable pipette tips, the improved pipette tip, hereinafter referred to as the "soft seal" tip, includes a portion of the open tubular proximal end comprising a frustoconical open top which is tapering downwardly and inwardly to join in a region ring seal with a hollow part mainly cylindrical of the pipette tip. The open top has a sufficient inner diameter to axially receive the distal end of a standard pipette tip mounting shaft. The annular sealing region is formed by means of the transition or connection line of the frustoconical open upper part with the middle part of the pipette and embraces an annular side wall with a thickness of .20 to .50 mm. The middle part has an inside diameter in the sealing region which is smaller with respect to the diameter of the pipette mounting shaft, a thin elastic annular side wall with a thickness of .20 to .50 mm and an axial length of .25 to .65 cm. Therefore, while the distal end of the mounting shaft fits into the elongated open end of the pipette tip, the frustoconical outer surface of the mounting shaft meshes with the inner surface of the sealing region at the bottom of the part. Open top of the pipette tip to stretch the annular sealing region or line out radially when the mounting shaft is inserted in the proximal part, thereby creating a watertight seal relative to the fluids between the sealing zone and sealing region. In addition to the proximal portion, the improved pipette tip includes a tubular distal portion that extends from the middle portion and terminates at a relatively narrow distal end that is open to pass fluid through the tip during operation of the pipette device . Finally, the improved pipette tip preferably comprises lateral stabilization means on its inner surface adjacent to the sealing region for coupling the outer surface of the mounting shaft when it is inserted in the proximal part in order to stabilize the tip laterally. on the axis. Such lateral stabilization means preferably comprise at least three circumferentially spaced contacts extending inwardly from the inner surface of the proximal portion of the tip adjacent to the sealing region to engage the outer surface of the mounting shaft when inserted in the next part in order to laterally stabilize the tip on the shaft. In this respect, the diametric spacing of the contacts is such that the contacts engage a little and allow the distal end of the shaft to pass without circumferential stretching of the side walls from which the contacts extend. In this way, the contacts are combined with the sealing region in order to provide lateral support to the pipette tip on the mounting shaft and prevent the tip from moving laterally when external lateral forces are exerted on the distal part of the tip. the tip during the explosion. Although the improved pipette tip according to the above description represents an important advance with respect to the standard pipette tips in relation to the axial forces that are necessary to install the tip on the pipette mounting shaft as well as to eject the pipette. tip of the pipette mounting shaft, there is still a need to reduce the risk of the pipette user suffering injuries due to repetitive movement and the desire to further minimize the axial forces needed for a stable installation of the tip of pipette on the pipette mounting shaft as well as for an expulsion of the pipette tip from the pipette mounting shaft. The present invention satisfies these needs.

SUMMARY OF THE INVENTION In order to meet the ideal criteria unattainable until now that disposable plastic pipette tips (i) are easy to install on a pipette tip mounting shaft to form a fluid tight connection to the shaft which is so secured that the tip will not present lateral oscillatory movements on the axis nor will it disengage from the jammed axis accidentally during normal use of the pipette (ii) then it will easily be ejected from the mounting shaft by means of the application of Minimum axial installation and ejection forces, for example forces of about one pound or less, the present invention has adopted a unique approach. It incorporates into the air displacement pipette the concept of zones and regions of annular seal axially separated and of lateral support mainly cylindrical in the axis of assembly and the tip of the pipette, respectively. In addition, means are provided to ensure a uniform depth of penetration of the mounting shaft into the pipette tip in order to maintain uniform tip interference with the mounting shaft when the subsequent tips are installed on the mounting shaft and ejected of the same.

In particular, the present invention comprises a combination of mounting shaft for pipette tip and pipette tip in an air displacement pipette. The mounting axis comprises an elongated body in axial form including a distal end and axially spaced apart and mainly cylindrical outer surface regions defining an annular sealing zone and an annular lateral support zone. The pipette tip is an elongated tube comprising an open distal end, an open conical distal end, and axially spaced and primarily cylindrical internal surface regions defining an annular sealing region and an annular lateral support region. The outer diameter of the annular sealing zone on the mounting shaft is slightly larger than the inner diameter of the annular sealing region of the pipette tip and the lateral wall of the tip in the area of the annular sealing region it is thin enough that the annular sealing region expands slightly to form an interference fit and an air tight seal between the mounting shaft and the pipette tip when the sealing zone penetrates the sealing region. The axial separation of the sealing and support areas is practically equivalent to the axial separation of the sealing and support regions. Also, the outer diameter of the lateral support zone is a little smaller or practically equivalent to the inner diameter of the lateral support region on at least some part of the circumference of the support zone. What allows some minimum contact between the support region and region without creating a second air tight seal that could result in an unwanted increase in the axial forces required for the installation of the pipette tip on the shaft and the ejection of the pipette tip of the shaft. With such a structural configuration, when the sealing zone penetrates the sealing region, the support region receives the support zone and provides lateral support for this aspect which prevents transverse oscillatory movement of the pipette tip on the mounting shaft that could otherwise occur during the explosion of the pipette tip and the undesirable unclogging of the tip from the shaft. In addition, the preferred embodiment of the present invention includes the hermetic adjustment of controlled interference air and the lateral annular support region and region, as well as the cooperative means on the pipette and the pipette tip to limit the axial path of the tip on the mounting axis. This ensures the uniform depth of penetration of the mounting shaft into the pipette tip to keep the desired interference of the tip uniform with the mounting axis while the subsequent tips are installed on the mounting shaft and are ejected from the assembly. mounting shaft, and will be able to notice from the outgoing structure of the pipette tip described in United States Patent 4,824,641. Due to the structural features of the cooperative described above of the pipette tip and mounting shaft, the combination of the pipette tip of the present invention has proven to require only axial forces of installation and expulsion of the pipette tip practically equivalent or by under a pound and provide a hermetic seal of stable air from the tip on the shaft which is safe with respect to the lateral oscillatory movement of the pipette tip on the mounting shaft. Therefore, the combination comprising the present invention requires the user of the pipette to generate so little thumb and hand strength that the repetitive installation and ejection of such pipette tips will likely not cause repetitive stress injury. In addition, for pipette tip and shaft combinations in which the interference fit between the sealing region and region is approximately .075 mm to almost .2 mm and the thickness of the pipette tip wall in the region of sealing is between .2 and .5 mm, it has been found that the tip installation and ejection forces related to the present invention can still be achieved and the lateral stability of the tip on the shaft increased more when there is little interference fit between the region and support area. The low interference fit is provided by the lateral support region of the tip with an internal diameter that is a little smaller than the external diameter of the lateral support zone of the shaft, for example less than .075 mm. In addition, when the shaft and tip are concentric and mainly circular in the support region and region, a tight seal of secondary air can be created between the support region and region without creating an unwanted increase in axial forces necessary for installation in the axis and expulsion of the same.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a standard manual pipette with a pipette tip installed on a mounting shaft adjacent to the lower end of the pipette tip ejector mechanism.

Figure 2 is a cross-sectional side view of one embodiment of the combination of pipette tip and mounting spindle according to the present invention.

Figure 3 is a side view of fragmentary fragmented section of the sealing region within the circle 3 for the pipette tip in Figure 2.

Figure 4 is an enlarged fragmentary side view of an upper part of the pipette tip and mounting shaft combination of Figure 2, showing the hermetic seal in relation to the fluids between the sealing region and the sealing zone, the coupling relationship of the region and support zone and a preferred embodiment of the cooperative means including a protrusion on the pipette tip to limit the penetration of the mounting shaft into the tip.

Figure 5 is an enlarged fragmentary side view similar to Figure 4 in addition to showing a first alternative embodiment of the cooperative means including a projection on the mounting axis to limit the penetration of the mounting shaft into the tip.

Figure 6 is an enlarged fragmentary side view similar to Figure 2 in addition to showing a second alternative embodiment of the cooperative means including a lower end of the pipette tip ejector tip to limit the penetration of the mounting shaft into the tip Fig. 7 is a cross-sectional side view of an alternative embodiment of the pipette tip and mounting shaft combination of the present invention that includes an extension of the mounting shaft to reduce the air volume effects associated with the pipettes of air displacement.

Figure 8 is a graph comparing the forces required to insert and eject a pipette tip from the pipette tip assembly and mounting shaft of the present invention into and from the mounting shaft with the insertion and ejection forces for the "soft seal" pipette tip and standard mounting shaft described in the currently pending patent application with serial number Figure 9 is a graph comparing the path of the pipette tip of the pipette tip assembly and mounting shaft of the present invention within the mounting axis with a standard pipette tip path and "soft seal" tip inside the standard pipette mounting shaft in response to the different insertion forces of the pipette tip.

Figure 10 is a graph comparing the lateral stability of a pipette tip of the pipette tip assembly and mounting spindle of the present invention on the mounting shaft with the lateral stability of a standard pipet tip and "tip" Soft seal "on a standard mounting spindle for tips installed with different pipette tip insertion forces.

Figure 11 is similar to Figure 4 and an amplified fragmentary side view of an upper portion and alternative embodiment from the pipette tip and mounting shaft combination of Figure 2 showing an axial reversion of the locations of the seal in relation to with the fluids between the sealing region and the sealing zone and the coupling relationship of the region and lateral support zone, the sealing region and region adjacent to the preferred embodiment of the cooperative means including a protrusion at the tip of the sealing region. Pipette to limit the penetration of the mounting shaft into the tip and the area and region of support being far apart form the cooperative means.

Figure 12 is similar to Figure 5 and an amplified fragmentary side view similar to Figure 11 showing an axial reversion of the sealing region and region related to the support region and region in addition to showing the first alternative mode of the means cooperatives which includes a projection on the mounting axis to limit the penetration of the mounting shaft into the tip, the support region and region being adjacent to the cooperative means and the sealing region and region being away from the cooperative means.

Figure 13 is similar to Figure 6 and an amplified fragmentary side view similar to Figure 11 showing an axial reversion of the sealing region and region in relation to the support region and region in addition to showing the second alternative embodiment of the cooperative means including a lower end of the pipette tip ejector of a pipette to limit the penetration of the mounting shaft into the tip.

Figure 14 is similar to Figure 4 and an amplified fragmentary side view of an upper part of the pipette tip and mounting shaft combination of Figure 2 showing the fluid tight seal formed by an interference fit between the sealing region and sealing zone, a small interference fit between the region and lateral support zone and a preferred embodiment of the cooperative means including a protrusion on the pipette tip to limit the penetration of the mounting shaft into tip.

Figure 15 is an enlarged fragmentary side view similar to Figure 5 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support zone of the shaft to provide better lateral support for the tip in the axis.

Figure 16 is similar to Figure 6 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support area of the shaft to provide better lateral support for the tip on the shaft.

Figure 17 is similar to Figure 7 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support area of the shaft to provide better lateral support for the tip on the shaft.

Figure 18 is similar to Figure 11 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support area of the shaft to provide better lateral support for the tip on the shaft.

Figure 19 is similar to Figure 12 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support area of the shaft to provide better lateral support for the tip on the shaft.

Figure 20 is similar to Figure 13 in addition to showing the small interference fit between the lateral support region of the tip and the lateral support area of the shaft to provide better lateral support for the tip on the shaft.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a standard manual pipette that is similar to the PIPETMAN pipette that Rainin Instrument Co. , assignee of the present invention, sells exclusively in the United States. The manual pipette is designated in Figure 1 by the number 10 and includes a pipette tip ejector mechanism 12 described in US Pat. No. 3,991,617, issued on November 16, 1976, which is considered to be reproduced as if it were inserted. to the letter.

The pipette 10 comprises a pressure button 14 connected by a rod 16 to a piston (not shown) located in the body or housing 18 of the pipette. The pressure button 14 can be depressed by a user exerting a downward force on it to cause a downward movement on the piston of the pipette. When the pressure button 14 is released, a quantity of sample liquid is sucked into a disposable pipette tip 20 releasably secured to a lower end of the pipette tip mounting shaft 22 of the pipette. Then, the sample can be transferred to another container by once again exerting a downward force on the pressure knob 14. After said use, it is common practice to eject the pipette tip 20 from the mounting shaft 22 and replace it with a new tip of pipette to repeat the operation of the suction pipette 10 and supply a new sample fluid.

The ejector mechanism of the pipette tip 12 is used to eject the tip 20 from the mounting shaft 22. In this respect, the mechanism 12 comprises a pressure button 24 connected with a rod located in a passage (not shown) provided in the upper part of the manually held housing 18 of the pipette 10. The passage and the rod are arranged so that they can impart the rod a translation movement parallel to an axis of the pipette opposite a spring (not shown) that normally impels the rod to an ascending position. A removable member or ejector arm of the tip 26 that includes a tubular upper end goes from the lower end of the rod and from the rod, passes through the general outer contour of the housing 18 of the pipette and reaches a sleeve 28. The sleeve 28 surrounds a lower conical end 30 of the pipette tip mounting shaft 22 that snugly receives the upper end of the disposable pipette tip 20. To eject the pipette tip 20 from the lower end of the mounting shaft 22, the subject subject the housing 18 of the pipette and, using its thumb, presses the pressure button 24. The downward force on the pressure button travels through the rod towards the ejector arm of the tip 26 and thus towards the sleeve 28, which presses down the upper end of the pipette tip. When the downward force transferred by the sleeve 28 exceeds the friction between the pipette tip 20 and the mounting shaft 22, the pipette tip is pushed from the mounting shaft. Upon release of the pressure button 24, the spring returns the tip ejector mechanism 12 to its normal position with the sleeve slightly spaced from the upper end of a replacement pipette tip that is inserted into the mounting shaft 22, leaving ready pipette 10 for your next suction and supply operation.

As already mentioned, in the case of standard pipettes of low or moderate volume, the pipette tip mounting shaft 22 has an inward axial taper of between two and five degrees from the longitudinal axis of the mounting shaft. Likewise, as already mentioned, the pipette tips of reduced or moderate volume for use with such a standard pipette tip mounting shaft comprise a frustoconical annular sealing strip or contiguous internal surface with the open proximal end of the tip for engage and seal with the tapered end of the pipette tip mounting shaft to give lateral stability to the tip on the shaft. The taper angle of the sealing surface is generally within approximately one degree of the two to five degrees taper inward of the mounting axis and the length of the sealing surface on the shaft is such that in forming the Annular seal tip is also almost stable on the shaft. In forming the desired annular seal, the frustoconical annular sealing region together with the equilibrium of the open proximal end of the pipette tip is necessary to stretch as a normal outward clamp for coupling the sloping surface of the pipette tip mounting shaft . Due to the length of the sealing region and the relatively thin side wall of the standard tip, the large plastic forces in the tip material resist such outward circumferential stretching and need the ejection of large axial forces on the tip to To install the standard tip on the mounting shaft and create the ring seal in relation to the necessary fluids. Frequently, axial forces of between 12 and 15 pounds are necessary to install a pipette tip on a standard mounting shaft and create the watertight seal in relation to the desired fluids. Such axial forces are generated by the hand and forearm of the pipette user when a pipette tip mounting shaft is applied within a pipette tip normally held in a pipette tip mounting stand. Of course, when it is desired to eject such a firmly installed tip from a pipette tip mounting shaft, an axial force of approximately ten (10) pounds should be applied at the upper edge of the pipette tip to resolve the frictional forces between the pipette tip and the shaft, and to eject the tip of the shaft.

The relationship between the forces of insertion and expulsion of the tip is described by curve 60 of Figure 8 for a standard pipette tip of 250 ml, the tip insertion forces increasing from 0 to almost 20 pounds at a point 62 wherein the tip engages an ejector mechanism of the related pipette device. As already described, the downward ejection forces of the tip are exerted by the user when pressing with his thumb on the top of the push button 24 to transfer the axial force through the ejector arm 26 to the top of the tip of pipette 20. As indicated in figure 8, to expel the standard pipette tip from its associated mounting shaft it is necessary that the user of the pipette generates an ejection axial force of approximately 12 pounds. In the course of several repetitive ejection operations, the user's thumb and hand will suffer physical stress. What frequently produces repetitive injuries in the thumb and hand and in extreme cases carpal tunnel syndrome. In an attempt to solve these problems, the aforementioned Soft Seal pipette tip design and described in the currently pending United States patent application was developed. As described in curve 70 of Figure 8, the Soft Seal pipette tip design facilitates easy and firm installation of a pipette point on the mounting shaft and easy ejection of the pipette tip from the pipette shaft. Assembly by means of the application of axial forces of installation of approximately six (6) pounds and axial forces of expulsion of approximately three (3) pounds. In figure 8, point 72 describes the applied force necessary to insert and eject the Soft Seal tip to and from a location on the standard pipette mounting shaft where the tip engages with the tip ejection mechanism of an associated pipette. The significant decrease in axial insertion and ejection forces related to the Soft Seal pipette tip when compared to those of a standard pipette tip is clear from the comparison of curve 70 with curve 60.

As already indicated, the present invention provides a novel mounting spindle and a unique pipette tip tailored to the mounting axis in such a way that it is even easier for the user to insert the tip into the spindle in an adjustment position for the fluids in which the tip is secured against lateral oscillatory movements and unwanted displacement of the shaft and, after use, it becomes even easier for the user to eject it. Such operations of tip insertion and ejection require that the user of the pipette only exert forces of insertion and expulsion of the axial tip of approximately one pound or less, hence reducing the risk that the user of the pipette suffers some injury due to repetitive movement. As described in curve 80 of figure 8, the design of the present invention, hereinafter referred to as "LTS" tip and / or axis, favors the easy and firm installation of the pipette tip of the present invention in its Related mounting shaft and easy ejection of the pipette tip from the mounting shaft by application of installation and ejection forces of approximately one (1) pound. In Figure 8, point 82 describes the force exerted necessary to insert and eject the LTS tip to and from a location on the mounting axis of the present invention where the tip engages a tip insertion boss to limit the penetration of the shaft inside the tip. As will be described later, in different embodiments of the present invention, such projection comprises a projection on the tip, the axis or the base of the tip ejector mechanism of the related pipette. The significant decrease in insertion and ejection forces related to the LTS pipette tip when compared to the Soft Seal tip and the standard pipette tip is clear from the comparison of curve 80 with curve 70 and 60 of Figure 8 In Figure 9, the relationship between the insertion force of the pipette tip and the distance traveling through a tip on a related pipette tip mounting shaft is described in a graph for the 250 ml LTS tips, of Soft and standard seal. Curves 100 and 110 describe the relationship between the insertion force and the path of the Soft and Standard Seal tips on standard mounting shafts, respectively. In this regard, the trajectory of the soft and standard seal tips is limited by the pipette tip ejection mechanism that is attached to the pipette tip as described in points 102 and 112, respectively. Curve 90 describes the relationship between the insertion force and the path of the LTS pipette tip on a LET mounting shaft. The trajectory of the LTS pipette tip is restricted by the aforementioned projection which engages the LTS tip according to the description of point 92 of curve 90. The significant increase in the tip path per unit of insertion force related to the pipette tip of the present invention once compared to the Soft Seal tip and the standard is evident from the comparison of curves 9'0, 100 and 110 of FIG. 9.

In Figure 10, the relationship between the insertion force of the pipette tip and the lateral stability of a pipette tip on its associated axis is described in a graph for the LTS 250 ml, Soft Seal and standard tips. In the case of Standard and Soft Seal pipette tips, the axial location of the pipette tip on the standard pipette tip mounting shaft is the point at which the pipette forms an air tight seal with the axis of the pipette. assembly and is located near or against the bottom of the pipette tip ejector mechanism for the related pipette. In the case of the LTS pipette tip, the axial location of the tip is defined by the aforementioned projection. Each pipette tip is subjected to a stability test by "exploding" the pipette tip during normal use of the pipette. That is to say, after sucking a volume of liquid into the distal end of the pipette tip, the pipette is moved into a receptacle in which the distal end of the tip is placed at an inclination to the side of the receptacle and at least a portion of the volume of liquid sucked is supplied by the operation of the pipette, during such positional control of the pipette tip, the distant end touches the side of the receptacle (for example, "explosion"). During this period, lateral forces are exerted on the distal end of the pipette tip which tends to swing the tip oscillatingly on its mounting axis. Figure 10 describes the number of cycles of "explosions" needed to unclog the pipette tip from its associated mounting shaft for different insertion forces. Curve 120 describes the relationship of the insertion force for lateral stability in the case of a standard pipette tip while curve 130 describes the relationship in the case of a Soft Seal pipette tip. Curve 140 describes the relationship of lateral force for lateral stability in the case of the LTS tip of the present invention. In Figure 10 it can be seen that the lateral stability of the LTS tip is basically constant above the 50"burst" cycles before unblocking the LTS tip from its associated mounting axis. This uniform stability ranges from the insertion force of approximately one pound. As for the standard pipette tip and Soft Seal tip, lateral stabilities that approximate that of the LTS pipette tip can only be achieved thanks to the insertion forces of approximately 15 pounds or more. For more normal insertion forces of approximately 10 pounds, unblocking standard pipette tips and Soft Seal from their mounting shafts associated with approximately 25"burst" cycles. Therefore, Figure 10 clearly describes the best lateral stability for the LTS pipette tip on its associated mounting shaft as compared to the standard volume and Soft Seal pipette tips of comparable volume.

A preferred embodiment of the structure of the pipette tip and mounting shaft combination of the present invention is described in Figure 2 and is shown in more detail in Figure 4. As described therein, the mounting shaft 32 comprises a axially elongate body including a distal end 34 and externally cylindrical and axially separated outer surface regions defining an annular sealing region 36 adjacent to the distal end and an annular lateral support area 38 at the distal end 34 near the end of the shaft 32 The pipette tip is represented by the number 40 and is an elongated plastic tube comprising an open proximal end 42, an open conical distal end 44 and internally cylindrical and axially separated inner surface regions defining an annular sealing region 46. and an annular side support region 48 for engagement with the sealing and support areas 36 and 38, respectively, on the mounting shaft. 32. As used in the present invention, "mainly cylindrical" means an annular surface with an axial taper of one degree and one degree and one-half or less.

Figure 3 shows in detail a preferred embodiment of the sealing region 46 and comprises the part of the pipette tip 40 of Figure 2 within the circle 3. As shown, the sealing region 46 is formed by a reinforcing projection. primarily of inwardly extending V-shaped form 49 extending radially inwardly from the side wall 50 of the pipette tip 40. The innermost surface of a reinforcing projection 49 forms a very narrow annular sealing band or line for coupling with the mainly cylindrical sealing zone 36 of the pipette tip mounting shaft 32 to form the airtight air seal described above between the tip and the mounting shaft.

According to Figure 4, the outer diameter of the annular sealing area 36 is slightly larger than the internal diameter of the annular sealing region 46 in the pipette tip 40 and the side wall 50 of the tip in the area of the annular sealing region 46 is sufficiently thin that the annular sealing region expands a little to form an interference fit and air tight seal between the mounting shaft 32 and the pipette tip 40 when the sealing zone 36 penetrates sealing region 46. In practice, it has been found that the desired interference fit is formed when the difference in outer diameter of the annular sealing zone and the inner diameter of the annular sealing region is at least. 075 mm (mm). Furthermore, it has been found that in practice the thickness of the wall of the pipette tip in the area of the sealing region 46 is preferably between .20 and .50 mm.

According to FIGS. 2 and 4, the axial separation of the sealing and support areas is practically equal to the axial separation of the sealing and support regions. Also, the external diameter of the lateral support zone 38 is a little less than, or practically equal to, the internal diameter of the lateral support region over at least a certain part of the circumference of the support zone. What allows a certain minimum contact between the area and support region without creating a hermetic seal of secondary air that would result in an undesirable increase in axial forces necessary to install and eject the pipette tip on the shaft and from the same . With said structural configuration, while the sealing zone 36 penetrates the sealing region 46, the support region 48 receives the support zone 38 and provides lateral support for it, which prevents transverse oscillatory movement of the pipette tip. 40 on the mounting axis 32, which could otherwise occur during the "explosion" of the pipette tip and the inherent unwanted unclogging of the tip from the shaft. In this aspect, it is preferred that the axial spacing of the region 38 and lateral support region 48 of engagement from the sealing region and region (36, 46) be substantially equal to the internal diameter of the pipette tip 40 in the region of support. Said length ratio provides excellent lateral stability for the pipette tip 40 on the mounting shaft 32.

Further, according to FIGS. 2 and 4, the present invention includes cooperative means 52 on the pipette of the present invention and the pipette tip 40 to limit the axial path of the tip on the mounting shaft 32. Which ensures the depth Uniform penetration of the mounting shaft into the pipette tip to maintain uniform interference of the tip with the mounting shaft while mounting the subsequent tips on the mounting shaft and expelling it. In the embodiment of Figures 2 and 4, said cooperative means 52 comprises an annular projection 53 facing upwards and directed inwardly on the inner surface of the pipette tip 40 immediately adjacent to the lateral support region 48. The projection 53 is designed in such a way that the upper surface thereof is coupled to a downward facing surface as the lower part 54 of the distal end 34 of the mounting shaft 32 in an outer circumferential part thereof.

The alternative embodiments of the cooperative means 52 are described in FIGS. 5 and 6. In FIG. 5, the cooperative means 52 comprises an annular projection 53 facing downwards directed outwardly on the pipette tip mounting axis 32 which after the Insertion of the shaft into the open proximal end 42 of the tip engages the upper annular edge 56 of the tip to prevent further penetration of the shaft into the tip. In Figure 6, the cooperative means 52 is described as comprising a lower part 58 of the jacket 28 of the pipette tip ejection mechanism described in relation to Figure 1. When the surface of the lower part 58 is coupled to the annular edge 56 of the pipette tip 40, further penetration of the mounting shaft 32 into the pipette is prevented.

While in the foregoing, particularly preferred embodiments of the pipette tip of the present invention have been described in detail, it is possible to make changes and modifications without departing from the spirit of the present invention. For example, FIG. 7 describes an alternative embodiment of the present invention comprising the cooperative means 52 as described in FIGS. 2 and 4, respectively. In addition to the structure of Figures 2 and 4, the embodiment of Figure 7 comprises a mainly cylindrical extension 62 from the bottom of the part 34 of the distal end of the mounting shaft 32. The extension 62 is coaxial with the mounting axis and comprises an outer side wall 63 spaced from the inner surface of the pipette tip 40. The extension 62 functions to decrease the volume of air captured in the pipette of the present invention and reduce the effects of air volume commonly associated with the Air displacement pipettes.

In addition, Figures 11, 12 and 13 describe alternative embodiments of the present invention in which the sealing region 36 and region 46 and the support region 46 and region 46 are axially inverted from the locations indicated in Figures 4, 5. and 6, respectively. As shown in Figure 11, the zone 36 and the sealing region 46 lie on one side of the cooperative means 52 while the support zone 38 and region 48 are located away from the cooperative means 52. In the figures 12 and 13, sealing zone 36 and region 46 are on one side of cooperative means 52 and support zone 38 and region 48 are away from cooperative means 52.

Still further, Figures 14, 15, 16, 17, 18, 19 and 20 are similar to Figures 4, 5, 6, 7, 11, 12 and 13, respectively, and show optional embodiments of the present invention in which there is a small interference fit between the lateral support region 48 and the support zone 38 to further improve the lateral stability of the tip 40 on the shaft 32 without inducing an unwanted increase in the axial forces necessary to install and eject the tip of the axis. About, and as described in each of the figures from 14 to 20, it has been found that as for the pipette tip and shaft combinations in which the interference fit between zone 36 and sealing region 46 is from approximately .075 mm to almost .2 mm and the thickness of the wall of the pipette tip in the sealing region 46 and in the lateral support region 48 is between .2 and .5 mm, the lateral stability of the tip 40 on shaft 32 can be increased while maintaining the minimum desired forces of installation and ejection of the tip related to the present invention when there is a minor interference fit between the region and support zone. Minor interference is provided by the lateral support region 48 of the tip 40 with an inner diameter that is slightly smaller than the external diameter of the lateral support zone 38 of the shaft 32, for example below .075 mm. In addition, when the axis 32 and tip 40 are concentric and mainly circular in the region 38 and support region 48, a hermetic seal of secondary air can occur between the support region and region without giving rise to an unwanted increase in the forces axially necessary for the installation of the tip on the shaft and the ejection of the shaft. In the embodiments of Figs. 14 to 17, the minor interference fit is provided by controlling the axial taper of the tip sidewall between the region and sealing zone for tapering slightly inward in a downward direction such that the side wall of the tip is coupled to the external side of the shaft in the support area. In the embodiments of Figures 18 to 20, the minor interference fit is provided by controlling the axial taper of the distal end of the shaft to taper slightly outwardly in an upward direction so that the outer side engages within the tip in the region of support.

Accordingly, the present invention will be limited only in scope to the terms contained in the following claims.

Claims (18)

CLAIMS An air displacement pipette (10) comprising a pipette tip mounting shaft (32) and a pipette tip (40) including axially supporting zones (36, 38) and support regions (46, 48) separate, annular coupling and mainly cylindrical sealing, respectively, the annular sealing region comprising a narrow annular sealing surface (49) towards the inside of a side wall (50) of the pipette tip which in the region of The seal (46) is thin enough so that the annular sealing region expands a little and forms an interference fit and air tight seal between the sealing surface (49) and the sealing zone (36) on the sealing shaft. assembly (32) when the sealing zone (36) penetrates the sealing region (46).
1. The pipet of claim 1 further comprising the means (52) to ensure uniform depth of penetration of the mounting shaft into the pipette tip to preserve uniform interference of the tip with the mounting shaft while the tips are mounted subsequent on the axis and are expelled from it. In an air displacement pipette (10), the combination comprising:
2. A pipette tip mounting shaft (32) comprising an axially elongate body including a distal end (34) and axially spaced outer surface regions defining an annular sealing zone (36) and an annular lateral support zone (38) ) ,-Y
3. A pipette tip (40) comprising an elongated tube having an open proximal end (42), an open conical distal end (44) and annular or primarily cylindrical and axially separated internal surface regions that define an annular sealing region ( 46) and a lateral annular support region (48) for coupling with the sealing zone (36) and lateral support zone (38), respectively, the annular sealing region comprising a narrow annular sealing surface (49) toward the inside of a side wall (50) of the pipette tip which in the sealing region (46) is thin enough so that the annular sealing region expands a little and forms an interference fit and airtight air seal between the sealing surface (49) and the sealing zone (36) on the mounting shaft (32) when the sealing zone penetrates the sealing region.
4. The combination according to claim 3, wherein the annular sealing zone (36) on the mounting shaft (32) has an outer diameter slightly larger than an inner diameter of the annular sealing region (46) in the pipette tip and the pipette tip (40) in an area that includes the annular sealing region (46) it encompasses a side wall that is thin enough that the annular sealing region expands a little to form an interference fit and air tight seal between the mounting shaft and the pipette tip when the sealing zone penetrates the sealing region .
5. The combination according to claim 4, wherein the side wall has a thickness between .2 and .5 mm.
6. The combination according to claim 4, wherein the sealing region (46) has an inner diameter that is at least .075 mm less than the outer diameter of the sealing zone (36).
7. The combination according to claim 3, wherein the axial separation of the sealing zone (36) and the support zone (38) is substantially equal to the axial separation of the sealing region (46) and the sealing zone (46). sealing (48) so that the sealing zone penetrates the sealing region and provides lateral support for it which prevents transverse oscillatory movements of the pipette tip on the mounting shaft that could otherwise occur during the explosion of the pipette tip and the inherent undesirable unclogging of the tip from the shaft.
8. The combination according to claim 3, wherein the axial separation of the lateral support region and region from the sealing region and region is substantially equal to an internal diameter of the pipette tip in the support region.
9. The combination according to claim 3 further comprising cooperative means (52) on the pipette shaft and pipette tip to limit the axial trajectory of the tip on the mounting shaft to ensure the uniform depth of penetration of the mounting shaft inside the tip to preserve the uniform interference of the tip with the mounting axis while the successive tips are installed on the mounting shaft and ejected therefrom.
10. 10. The combination according to claim 9 wherein the cooperative means (52) comprises an annular rising projection (53) on an inner surface of the pipette tip to be coupled to a lower surface (54) of the distal end (34) of the pipette tip mounting shaft.
11. 11. The combination according to claim 9 wherein the cooperative means (52) comprises an annular projection extending outwardly downwardly (53 ') on the pipette tip mounting shaft (32) to be coupled to one end face up (56) of the pipette tip.
12. 2. The combination according to claim 9, wherein the cooperative means (52) comprises a lower end (58) of a pipette tip ejector (26) included in the air displacement pipette (10). In the air displacement pipette (10), the combination comprises:
13. A pipette tip mounting shaft (32) including an axially elongate body comprising a distal end (32) and axially spaced annular outer surface regions defining an annular sealing zone (36) and a lateral support zone annular (38);
14. A pipette tip (40) comprising an elongated tube having an open distal end (42), an open conical distal end (44) and axially spaced annular inner surface regions defining an annular sealing region (46) and an annular lateral support region (48) for coupling with the sealing zone and the lateral support zone, respectively, the annular sealing region (46) comprising a narrow annular sealing surface (49) into a wall side (50) of the pipette tip which in the sealing region (46) is thin enough so that the annular sealing region expands a little and forms an interference fit and airtight seal of air between the sealing surface (49) and the sealing zone (36) on the mounting axis when the sealing zone penetrates the sealing region; Y Cooperative means (52) in the pipette (10) and pipette tip (40) to limit the axial trajectory of the tip on the mounting shaft (32) to ensure the uniform depth of penetration of the mounting shaft into the tip of the tip. Pipette to keep uniform the interference of the tip with the mounting axis while the subsequent tips are installed on the mounting shaft and ejected from it.
15. A pipette tip mounting shaft (32) designed to reliably receive and support a pipette tip (40) that includes substantially cylindrical and axially separated internal surface regions that define an annular sealing region (46) and a region of lateral annular support (48), the pipette tip mounting shaft comprising: an axially elongate body for axially receiving such a pipette tip, the axially elongated body comprising: a part of the distal end for supporting a pipette (10) to extend axially therefrom, a far end (34) away from the near end portion, a substantially cylindrical outer surface region in the axially extended body adjacent to the distal end and defining an annular sealing zone (36) for engaging the annular sealing region (46) ) inside the pipette tip (40), and a substantially cylindrical external surface region in the axially elongated body separated from the annular sealing region (36) and defining an annular lateral support zone (38) with an outer diameter a little smaller than the inner diameter of the support region lateral ring (48) on the inner surface of the pipette tip (40).
16. A pipette tip (40) comprising an elongated tube having an open distal end (42), an open conical distal end (44) and annular or mainly cylindrical and axially separated internal surface regions (46) and a supporting region lateral ring (48) for coupling with annular or mainly cylindrical and axially separated external surface regions defining an annular sealing region (36) and an annular lateral support zone (38) of a pipette tip mounting shaft (32) ), the annular sealing region comprising a narrow annular sealing surface (49) towards the inside of a side wall (50) of the pipette tip which in the sealing region (46) is thin enough so that the The sealing region expands a little to form an interference fit and air tight seal between the sealing surface (49) and the sealing area (36) on the mounting shaft (32) when the sealing area penetrates the region sealing. In an air displacement pipette (10), the combination comprising: a pipette tip mounting shaft (32) having an elongate body including a distal end (34) and annular or primarily cylindrical and axially separated outer surface regions (36) and an annular lateral support zone (38); a pipette tip (40) comprising an elongated tube having an open proximal end (42), an open conical distal end (44) and annular or mainly cylindrical and axially separated internal surface regions (46) and a supporting region annular lateral (48) for coupling with sealing zone (36) and region (38), respectively; the annular sealing region (36) on the mounting shaft with an external diameter that is slightly larger than the internal diameter of the annular sealing region (46) of the pipette tip; the pipette tip (40) in an area including the annular sealing region (46) encompassing a narrow annular sealing surface (49) into a side wall (50) of the pipette tip which in the sealing region (46) is thin enough that the annular sealing region expands a little to form an interference fit and air tight seal between the mounting shaft (32) and the pipette tip (40) when the region sealing (36) penetrates the sealing region (46); the annular support zone (38) on the mounting shaft (32) with an outer diameter that is slightly larger than an inner diameter of the annular support region (48) on the pipette tip; Y the pipette tip (40) in an area including the annular support region (48) comprising a side wall thin enough so that the annular support region is slightly expanded to form a smaller interference fit between the mounting axis and the pipette tip when the support zone (38) penetrates the support region.
17. 17. The combination according to claim 16, wherein the side wall of the pipette tip in the sealing region (46) and in the support region (48) has a thickness of between .2 and .5 mm.
18. 18. The combination according to claim 17, wherein the sealing region (46) has an inner diameter that is from about .075 mm to about .2 mm less than the outer diameter of the sealing zone (36) and in wherein the support region (48) has an inner diameter that is smaller than the outer diameter of the support zone (38) by .075 mm or less.