WO2006005923A1

WO2006005923A1 - Liquid dispensing system

Info

Publication number: WO2006005923A1
Application number: PCT/GB2005/002688
Authority: WO
Inventors: Andrew Wheatstone
Original assignee: Norgren Limited
Priority date: 2004-07-08
Filing date: 2005-07-08
Publication date: 2006-01-19

Abstract

A liquid dispensing system comprises a disposable container (20) having a reservoir (21, 31) of liquid in communication with a tube (22, 32) of small diameter defining a chamber retaining a measured volume of liquid, and a connection (24) to air pressure means (25), adapted to transfer a measured volume from the reservoir (21) to the chamber, and to expel the measured volume from the chamber through an outlet (23). The use of air pressure to expel the liquid ensures that it is fully dispensed without contamination. The system is also accurate as the measured volume is transferred to the chamber by the air pressure, so that it is not necessary to provide valves or seals for dispensing the liquid volume.

Description

LIQUID DISPENSING SYSTEM

This invention relates to a liquid dispensing system for dispensing sub- millilitre volumes of liquid. Such small volumes are used in laboratory experiments and tests such as in vitro diagnosis of conditions from samples such as blood serum, urine and the like.

In vitro diagnosis requires the use of between two and five reagents (most commonly three) stored in a machine and added successively to a prepared sample. The reagents are generally expensive, so that it is advantageous to use as little as possible for each test, particularly in view of the fact that medical staff require an increasing number of tests to be done in order to confirm diagnoses. It is important that the volumes of reagent used are measured accurately, so that the test results are accurate and repeatable. Currently, the amount of reagent used is in the range of 200 to 1000 microlitres, as it is difficult and expensive to make a diagnostic machine which can dispense lesser volumes from a reservoir sufficiently accurately. The liquid is usually dispensed via pipettes or syringes, using systems involving valves and seals, which suffer from hysteresis and so affect accuracy.

A further problem with dispensing liquids is cross-contamination, which occurs when the reagent touches samples, other reagents or non-sterile surfaces. Drops of liquid tend to be left on the dispenser, and these may be difficult to remove without touching. Obviously, cross-contamination needs to be avoided if the tests are to be accurate and repeatable.

The aim of the invention is to increase the accuracy of dispensing small volumes of liquid (from 0.5 to 80 microlitres) from a machine, while avoiding cross-contamination, and providing ease of replenishment of the liquids in the machine, such as by the use of disposable containers. According to a first aspect of the invention, a liquid dispensing system comprises a disposable container having a reservoir of liquid in communication with a tube of small diameter defining a chamber retaining a measured volume of liquid, and a connection to air pressure means, adapted to transfer a measured volume from the reservoir to the chamber, and to expel the measured volume from the chamber through an outlet.

The use of air pressure to expel the liquid ensures that it is fully dispensed without contamination, as the air pressure will blow all of the liquid out, without leaving any drops which can touch anything else. This also contributes to the accuracy of the volume used. The measured volume is also transferred to the chamber by the air pressure, so that it is not necessary to provide valves or seals for dispensing the liquid volume.

In one embodiment air pressure acting on the reservoir transfers the volume into the chamber. Air pressure then acts in the chamber to expel the liquid.

In another embodiment air is injected at a given location into a column of liquid extending from the chamber to the reservoir, to define the volume in the chamber. The air pressure then expels the measured volume while supporting the column of liquid leading to the reservoir.

In each embodiment the diameter of the tube is chosen so that the surface tension at the outlet will support the column.

Preferably, the containers are of suitable plastics material, and may be formed as a strip that is fed through a machine performing the dispensing. The small diameter tube and the reservoir may be integrally moulded. Preferably, the outlet from the tube is in the form of a nozzle. The diameter of the tube at the outlet is chosen so that the surface tension formed at the outlet will support the column. Alternatively, the outlet may be a "duck bill" valve. The "duck bill" valve enables a larger amount of liquid, or a liquid with a low surface tension, to be supported in the tube. The "duck bill" valve will be adapted to open when the gas is transferred into the tube.

Preferably the tube depends from the reservoir and the connection to the pressure means extends at substantially 90° to the tube.

The pressure means may be integral with the disposable container. Thus, the pressure means may comprise a bulb of pressurized gas that is actuated by a dispensing machine. Alternatively, the pressure means may form part of the liquid dispensing system and be adapted to engage the connection on the tube of the container.

Air pressure acting on the reservoir may transfer the liquid into the chamber.

A further connection may be provided on the tube adjacent the outlet to communicate with a vacuum/partial pressure source to draw liquid from the reservoir into the tube.

The pressure means may be integral with the vacuum/partial pressure source. Thus, a diaphragm pump or bellows arrangement may provide both the pressure to dispense the liquid and the vacuum to draw liquid from the reservoir for the subsequent dispense. Preferably, this occurs on successive cycles of the diaphragm pump or bellows arrangement. The tube may have corrugations or be of helical form. This allows a greater amount of liquid to be supported in the tube in comparison to a straight tube. Further, these arrangements have space saving benefits thus allowing the container to remain compact even when adapted to dispense larger quantities of liquid.

According to a second aspect of the invention, a liquid dispensing system comprises a disposable container having a reservoir of liquid in communication with a tube of small diameter defining a chamber retaining a column of liquid, the small diameter tube having a connection, at a predetermined location, to which pressure means is adapted to transfer a measured volume of gas into the chamber to expel a predetermined volume of liquid from the chamber through an outlet.

Embodiments of the various aspects of the invention are illustrated, by way of example only, in the accompanying drawings, in which:

Figure 1 shows a liquid dispensing system in accordance with the invention; and

Figure 2 shows another liquid dispensing system in accordance with the invention; and

Figure 3 shows a container of a liquid dispensing system in accordance with the invention;

Figure 4 shows in detail the bottom of the container of Figure 3 in use;

Figure 5 shows a modification of the container of Figure 3 ; and Figure 6 shows a second embodiment of the liquid dispensing system of the invention.

The liquid dispensing systems shown in the Figures are designed to dispense accurately liquid volumes in the range of 0.5 to 80μl (microlitres) , for use in diagnostic machines utilising two or more reagent liquids to test a sample such as blood serum or urine. The systems shown in the Figures use air pressure to expel a measured volume of liquid.

Figure 1 shows a liquid dispensing system in accordance with the invention. The system of Figure 1 comprises a disposable container 20 including a reservoir 21 of liquid attached to a capillary-type tube 22 of smaller diameter, ending in an open outlet nozzle 23. The diameter of the nozzle 23 is chosen so that the surface tension of the liquid at the nozzle will support the column of liquid in the tube 22 and the reservoir. Tube 22 has a small aperture 24 in its wall, at a predetermined location above the nozzle 23. The aperture 24 is connected to an air pressure dispensing system 25 (shown schematically) by a small diameter tube 26. The air dispensing system 25 comprises a source of air pressure, and a valve, together with control means to ensure that an accurate amount of air at a given pressure can be dispensed. The air dispensing system 25 will form part of the machine.

In use, the container 20 is installed in the machine with the tube 26 inserted in the aperture 24. When the liquid is to be dispensed, the air system 25 is actuated to inject air into the column of liquid through the tube 26 and aperture 24. This air forms a bubble 27 in the tube 22, separating the column of liquid into two chambers, a lower chamber 28 and an upper chamber 29 connected to the reservoir 21. The lower chamber 28 defines a measured volume of the liquid, as the bubble 27 will form in the same place each time. Further injection of pressurised air will apply sufficient force to overcome the surface tension at the nozzle 23, so that the measured volume is expelled from the tube 22. The air pressure is then removed, and the liquid re-fills the tube 22. The diameter of the aperture 24 is chosen so that the liquid will not enter the tube 26.

The embodiment of Figure 2 is also in accordance with the second aspect of the invention. The system of Figure 2 also comprises a disposable container 30 including a reservoir 31 of liquid connected via a capillary-type tube 32 of small diameter (of the order of 0.05 mm) to a tube 33 of slightly larger diameter (0.5mm) . The tube 33 has an open lower end defining a chamber connected to an outlet nozzle 34, and an open upper end 35 adapted to be attached to an air pressure dispensing system 36. The reservoir 31 is in communication with a second air pressure dispensing system 37. Both air pressure dispensing systems are shown schematically. The system 36 comprises a solenoid valve controlling flow of pressurised air from a source to the tube 32, while the system 37 is a more accurate system, with valves and a control means controlling the supply of air from a source to the reservoir, to dispense a measured volume of liquid from the reservoir 31. The systems 36 and 37 will form part of the machine.

In use, the container 30 is inserted into the machine, and connected to the systems 36 and 37. The system 36 has a sealed connection to the upper end 35 of the tube 32, while the system 37 is sealingly connected to the reservoir 31. When the liquid is to be dispensed, the system 37 is actuated, and a measured volume of liquid is forced out of the reservoir 31, through the tube 32 and into the chamber in the tube 33. The liquid runs down to the nozzle 34, where it is held by the surface tension. The system 36 is then actuated so that pressurised air is forced down the tube 33, expelling the measured volume of liquid from the chamber through the nozzle 34. The diameter of the tube 32 is chosen to be sufficiently small so that the air will not enter it to a significant extent. When the liquid has been expelled, the air pressure is removed. The tube 33 is then empty of liquid, and the liquid in the tube 32 remains there due to the surface tension at the junction of the tubes.

The embodiments shown in Figures 3 to 6 are similar to the embodiment of Figure 1 and like reference numerals have been applied to corresponding parts.

Figure 3 shows a liquid dispensing system in accordance with the invention. The system of Figure 3 comprises a disposable container 20 including a reservoir 21 of liquid attached to a capillary-type tube 22 of smaller diameter, ending in an open outlet nozzle 23. The diameter of the nozzle 23 is chosen so that the surface tension of the liquid at the nozzle will support the column of liquid in the tube 22 and the reservoir. Tube 22 has a small aperture 24 in its wall, at a predetermined location above the nozzle 23. The aperture 24 is connected to an air pressure dispensing system (not shown) by a small diameter tube 26. The air dispensing system comprises a source of air pressure, and a valve, together with control means to ensure that an accurate amount of air at a given pressure can be dispensed. The small diameter tube 26 is formed integrally with the container 20. The air dispensing system will form part of the machine.

The container 20 also has a plug 40, which seals an aperture in the reservoir 21 , through which the reservoir may be filled. The plug 40 includes a vent 41 that allows air into the reservoir 21 as liquid is dispensed therefrom. It will be appreciated that the vent 41 may be separate from the plug 40. The reservoir 21 has inclined inner walls 44 towards its base, adjacent the tube 22. The walls 44 allow the liquid within the reservoir 21 to drain into the tube 22.

The small diameter tube 26 has a seal 42 at its free end for forming a sealing connection with the air dispensing system. The seal 42 is an O- ring seal and is mounted within a circumferential groove 43 in the small diameter tube 26.

In use, the container 20 is installed in the machine with the tube 26 inserted into the air dispensing system (not shown) . When the liquid is to be dispensed, the air system is actuated to inject air into the column of liquid through the tube 26 and aperture 24 (as shown in Figure 4) . This air forms a bubble 27 in the tube 22, separating the column of liquid into two chambers, a lower chamber 28 and ah upper chamber 29 connected to the reservoir 21. The lower chamber 28 defines a measured volume of the liquid, as the bubble 27 will form in the same place each time. Further injection of pressurised air will apply sufficient force to overcome the surface tension at the nozzle 23, so that the measured volume is expelled from the tube 22. The diameter of the tube 22 and the amount of air injected in is chosen to ensure that no liquid trapped above the bubble 27 can be drawn past by gravity or a venturi effect and thus affect the dispensed quantity. The air pressure is then removed, and the liquid re-fills the tube 22. The diameter of the aperture 24 is chosen so that the liquid will not enter the tube 26. Alternatively, a non-return valve may be provided.

The formation of the bubble 27 also displaces the liquid of the upper chamber 29 back into the reservoir 21. The displaced liquid acts to agitate and promote mixing of the liquid in the reservoir, which is advantageous. This is particularly important when the liquid is colloidal. It will be appreciated that there will be instances where it may be preferable or necessary to use a gas other than air. For example, an inert gas may be needed to ensure that it does not react with the reagent being dispensed.

Figure 5 shows several modifications to the container of Figure 3, although like reference numerals have been assigned to like features. In particular, the tube 22 has a second small aperture 45 in its wall adjacent the nozzle 23. The aperture 45 is connected to a vacuum or partial pressure source (not shown) by a second small diameter tube 46. Once the liquid has been dispensed as described above by injecting air into the tube 22 through tube 26, the vacuum source is actuated to draw liquid from the reservoir 21 into tube 22 for the subsequent dispense. Thus, the vacuum source (not shown) promotes the refilling of the tube 22. This is particularly advantageous when a larger volume of liquid is to be dispensed or the liquid has a low surface tension and thus a smaller nozzle 23 is used to ensure sufficient surface tension can be generated to support the liquid in tube 22. Also, the use of a vacuum source is advantageous for particularly viscous fluids. The vacuum/partial pressure source is regulated so that it exerts sufficient force to draw liquid from the reservoir 21 into the tube 22, but the force is insufficient to draw liquid into the second small diameter tube 46.

The air dispensing system connected to tube 26 and the vacuum source connected to the tube 46 may be integrated together in a bellows or diaphragm pump arrangement. They may also form part of the disposable container 20 and be actuated by the machine in which the container is adapted to be mounted.

Figure 5 also shows a hollow cap 47 mounted within the reservoir 21 over the tube 22. The cap 47 has an open end and a closed end 49 and a plurality of slots extending axially part way through its circumferential wall from the open end. The cap 47 aids in preventing any particles in the liquid settling into the nozzle 22, which may affect the amount of liquid dispensed or the amount of particles in a given dispense volume.

Figure 6 shows a further modification in which the nozzle 23 is located at the free end of the tube 26, through which the pressure means 51 is connected. Dosing means 50 introduces a measure amount of liquid into the tube 26, which can then be expelled from the nozzle 23 by the transfer of gas into tube 26 from pressure means 51.

In a modification, the tube 22 has a plurality of axially spaced small apertures 24 in its wall, each aperture being in communication with a corresponding small diameter tubes 26. Each aperture is at a predetermined location above the nozzle 23. Each tube is connected to an air pressure dispensing system. The arrangement is such that different amounts of liquid are dispensed depending upon which of the plurality of tubes are supplied with air. Thus, a tube 26 near to the nozzle 23 will dispense less liquid than one further from the nozzle 23, when supplied with air.

In a further modification (not shown) , instead of providing a plurality of tubes 26 for dispensing different amounts of liquid there may be a single sliding air inlet. The sliding inlet can thus be positioned at various positions along the length of the tube 22 so that it dispenses an amount of liquid proportional to the distance of the sliding inlet from the nozzle 23.

In all of these embodiments it will be appreciated that the measured volume of liquid is expelled fully from the container, as air pressure is used to do this. No drops will remain to be removed by touching another surface, so that contamination is avoided. In the embodiments of the Figures the air pressure is used to measure the volume, so that valves and seals are not needed.

Claims

1. A liquid dispensing system comprises a disposable container (20) having a reservoir (21, 31) of liquid in communication with a tube (22, 32) of small diameter defining a chamber retaining a measured volume of liquid, and a connection (24) to air pressure means (25) , adapted to transfer a measured volume from the reservoir (21) to the chamber, and to expel the measured volume from the chamber through an outlet (23) .

2. A liquid dispensing system according to claim 1, in which air pressure acting on the reservoir (21) transfers the volume into the chamber.

3. A liquid dispensing system according to claim 2, in which air pressure then acts in the chamber to expel the liquid.

4. A liquid dispensing system according to claim 1, in which air is injected at a given location (24) into a column of liquid extending from the chamber to the reservoir, to define the volume in the chamber (28) .

5. A liquid dispensing system according to claim 4, in which the air pressure then expels the measured volume while supporting the column of liquid leading to the reservoir (21) .

6. A liquid dispensing system according to any preceding claim, in which the container (20) is of suitable plastics material.

7. A liquid dispensing system according to any preceding claim, in which the containers (20) are formed as a strip that is fed through a machine performing the dispensing.

8. A liquid dispensing system according to any preceding claim, in which the small diameter tube (22) and the reservoir (21) are integrally moulded.

9. A liquid dispensing system according to any preceding claim, in which the outlet (23, 34) from the tube (22, 33) is in the form of a nozzle.

10. A liquid dispensing system according to any preceding claim, in which the diameter of the tube (22) at the outlet (23, 34) is such that the surface tension formed at the outlet supports the column.

11. A liquid dispensing system according to any of claims 1 to 9, in which the outlet is a "duck bill" valve.

12. A liquid dispensing system according to any preceding claim, in which the tube (22) depends from the reservoir (21)

13. A liquid dispensing system according to any preceding claim, in which the connection to the pressure means (25) extends at substantially 90° to the tube (22) .

14. A liquid dispensing system according to any preceding claim, in which the pressure means (25) is integral with the disposable container (20) .

15. A liquid dispensing system according to any preceding claim, in which the pressure means (25) comprises a bulb of pressurized gas that is actuated by a dispensing machine.

16. A liquid dispensing system according to any of claims 1 to 13, in which the pressure means (25) forms part of the liquid dispensing system and is adapted to engage the connection (24) on the tube (22) of the container (20) .

17. A liquid dispensing system according to any preceding claim, in which a further connection (45) is provided on the tube (22) adjacent the outlet (23) to communicate with a vacuum/partial pressure source to draw liquid from the reservoir (21) into the tube (22) .

18. A liquid dispensing system according to claim 17, in which the pressure means (25) is integral with the vacuum/partial pressure source.

19. A liquid dispensing system according to claim 17 or claim 18, in which a diaphragm pump or bellows arrangement provides both the pressure to dispense the liquid and the vacuum to draw liquid from the reservoir (21) for the subsequent dispense.

20. A liquid dispensing system according to any preceding claim, in which the diaphragm pump or bellows arrangement provides the pressure to dispense the liquid and the vacuum to draw liquid from the reservoir (21) for the subsequent dispense on successive cycles.

21. A liquid dispensing system according to any preceding claim, in which the tube (22) has corrugations .

22. A liquid dispensing system according to any preceding claim, in which the tube (22) is of helical form.