Burettes And Pipettes

Abstract

Method and device for dispensing a predetermined amount of liquid which includes a storage means for holding liquid therein, a nozzle for dispensing the liquid from the storage means, and means for producing a symmetrical puff of gas about the nozzle side wall to remove droplets from the outlet of the nozzle.

Description

The present invention relates to burettes, pipettes, syringes and the like.

In the delivery of accurately measured quantities of liquid from a burette, pipette, syringe or the like, one of the limits of accuracy has always been that the liquid cannot be dispensed in units of less than one drop, the size of which will depend on the liquid being delivered, and the material and configuration of the delivery nozzle.

It is an object of this invention to provide a method and apparatus by means of which the accuracy of measurement of dispensing a liquid from an orifice can be greatly increased. This object is achieved by a method for removing droplets from the tip of the delivery nozzle of burettes, pipettes, syringes and the like. It is a further object of the invention to provide a method for stirring a liquid into which the tip of the delivery nozzle of a burette, pipette, syringe or the like, projects.

Accordingly the invention provides a method for removing droplets from the tip of the delivery nozzle of burettes, pipettes, syringes, and the like, or for stirring liquid into which the tip of said delivery nozzle projects, which comprises directing a puff of gas past said tip in the direction of delivery of liquid through said nozzle in such a manner as to symmetrically surround said tip. This method is effected by a device having a gas passage therein, an inlet to said passage adapted to be supplied with pressurised gas, and an outlet directed in the delivery direction of said delivery nozzle and arranged to allow egress of said pressurised gas adjacent to and symmetrically surrounding the tip of said delivery nozzle.

The method is performed by applying a short flow or puff of gas after the main delivery of the liquid has been completed, the flow or puff of gas being of sufficient intensity to blow off substantially all adhering liquid. The effect is to take the level of the liquid at the delivery nozzle always to a definite level. Thus, a puff of gas before delivery effects an adjustment of the liquid to this definite level, and a puff after a measured volume has been dispensed returns the liquid to the same level. The volume of liquid which has passed out of the apparatus thus accurately corresponds to the volume measured and no allowance or corrections have to be made for liquid adhering to the nozzle.

A preferred embodiment of the device of the invention comprises a cylindrical member for mounting coaxial with the delivery nozzle, to be spaced therefrom so as to provide an annular chamber, the end of the cylindrical member remote from the tip of the delivery nozzle fitting the nozzle tightly. The cylindrical member is conveniently provided with a side-tube as the inlet through which the gas can be applied, and has an outlet adjacent to and symmetrically surrounding the tip of the delivery nozzle. The side-tube preferably incorporates a valve, thereby preventing any suck-back of the gas after a puff, and it is convenient for the valve to be a press-button valve which is operated each time a puff of gas is required. The tip of the delivery nozzle of any burette, pipette, syringe or the like, forming part of the device, or to which the device is attached, is most desirably provided with a chisel-edge, and is preferably coplanar with the outlet of the cylindrical member. When the tip of the delivery nozzle extends beyond the outlet, the incorporation of a valve into the side-tube is not necessary for maximum effectiveness and accuracy.

An alternative embodiment is one in which instead of an annular chamber around the delivery nozzle constituting the gas passage, the gas passage is contained within the walls of the cylindrical member, and thus the device need not touch the delivery nozzle.

The gas used in operation of the device of the invention may be air, and the air can be applied conveniently from a source of compressed air such as a hand-operated bulb or syringe. Other preferred gases are nitrogen, carbon dioxide, or an inert gas such as argon. Sterile air may also be used when it is desirable to operate the device under sterile conditions.

The device of the invention is particularly useful in combination with a micrometer syringe, such as that sold under the registered trade-mark "Agla." In this case the delivery nozzle comprises a syringe needle, around which the cylindrical member is positioned. The capillary of the needle is of a very fine bore, and the finer the bore, the greater is the gas pressure require to remove the droplets; conversely, if the syringe is fitted with a shorter needle, the gas pressure required is decreased.

The invention therefore provides a means of obtaining a very high order of accuracy of dispensing liquid in a microtitration, particularly for volumes of liquid less than 500 microlitres. When a microtitration is performed the needle is cleared initially with a puff of gas; when the microtitration is performed with the needle above the surface of the solution in the receiving vessel, each drop of liquid delivered can be blown off by subsequent discharges of the gas. Thus liquid can be dispensed under sterile conditions, and the need for any contact with the sides of the receiving vessel is obviated.

The invention also provides a means of dispensing accurate volumes of liquid in chromatography procedures. Preferably the needle is held close to, but not in contact with, the support medium.

As well as its use in connection with syringes, the device of the invention provides a means for increasing the accuracy of dispensing liquid from a burette, pipette or the like. In this case, the device is most conveniently constructed as an adaptor for sliding onto the conical delivery nozzle of the measuring device.

The invention also provides a means for stirring a liquid, the flow of gas through the liquid or onto the surface simulating mechanical agitation.

In order that the invention may be more fully understood, preferred embodiments thereof, which are not to scale, will now be described, by way of illustration only, with reference to the accompanying drawings in which:

FIG. 1 is a vertical cross-section of a syringe in combination with a device according to the invention;

FIG. 2 is a cross-section of the tip of the syringe shown in FIG. 1;

FIG. 3 is a vertical cross-section of a burette in combination with an alternative form of a device according to the invention;

FIG. 4 is a vertical cross-section of a device according to the invention, similar to that shown in FIG. 3, showing its use as a stirring mechanism.

Referring first to FIG. 1, there is shown a syringe 1, fitted with a plunger 2 and a needle 3, in combination with a cylindrical member 4 forming an annular chamber 5. Chamber 5 is provided with an inlet 6 connected to a side-tube 7 fitted with a valve 8. Side-tube 7 is connected to a hand-operated bulb 9 of compressed air by rubber tubing 10. Chamber 5 has an outlet 11 adjacent to and surrounding the tip 12 of the syringe needle 3.

In operation, air is supplied from the bulb 9, the supply being controlled by the valve 8 in the side-tube 7. The air passes through the inlet 6 into the chamber 5, and hence through the outlet 11 removing liquid adhering to the tip 12 of the syringe needle 3.

The syringe 1 can be positioned in a horizontal plane, in which case the cylindrical member 4 and the syringe needle 3 may be extended and curved so that the tip 12 of the needle 3 is directedly vertically for delivery. It is often convenient to use a straight needle 3, fitted to the syringe 1 by means of a curved metal tube.

FIG. 2 shows the tip 12 of the syringe needle 3, the tip 12 having a chisel-edge 13 to facilitate the removal of adhering liquid.

In FIG. 3, the conical-shaped delivery nozzle 14 of a burette 15 is surrounded by a coaxial member 16. The upper end of the coaxial member 16 has a tapered opening adapted to fit precisely onto the tapered delivery nozzle 14. The same reference numerals as those used in FIG. 1 and 2 are employed here where applicable. The side-arm 7 is connected by rubber tubing 10 to a source of pressurised gas (not shown in this Figure).

FIG. 4 shows the delivery nozzle 17 of a measuring device (not shown in this Figure), the nozzle 17 projecting into a liquid 18 is contained in a vessel 19.

In operation a flow of gas passing through the outlet 11 of the chamber 5 causes agitation of the liquid 18, and thus effects stirring.

Claims

What we claim is:

1. A method of delivering a measured quantity of liquid from a burette, pipette, syringe or the like each of which includes storage means for storing a quantity of liquid, nozzle means coupled to said storage means, said nozzle means directed vertically downwards and having an outer side wall and a central bore with an outlet at the terminus of the bore, and means for dispensing a measured amount of liquid to be dispensed from said storage means through the central bore of said nozzle, the method comprising the steps of providing an annular chamber about the nozzle, said annular chamber having an inwardly disposed cylindrical wall extending about the nozzle and spaced therefrom and which extends towards said outlet but not below said outlet, the chamber only permitting the escape of gas from the chamber in the direction of the outlet and about the nozzle outer side wall; dispensing liquid from said storage means through said nozzle outlet; discontinuing said dispensation of liquid; and then directing a puff of compressed gas into the chamber to produce a symmetrical puff of gas flow between the outer side wall of the nozzle and the inwardly disposed cylindrical wall to discharge liquid adhering to the nozzle and permit its passage vertically downwards.

2. The method of claim 1 in which a hand operated bulb is coupled to the annular chamber and is squeezed to produce the puff of gas.

3. A device for delivering measured amounts of liquid comprising storage means for storing a quantity of liquid, nozzle means coupled to said storage means, said nozzle means having an outer side wall and a central bore with an outlet at the terminus of the bore, means for dispensing a measured amount of liquid from the storage means through the central bore of said nozzle, means for measuring the quantity of liquid dispensed, a hollow cylindrical member having an inner side wall, said cylindrical member, inner side wall and said nozzle outer side wall defining an annular chamber, said annular chamber extending about the nozzle outer side wall and spaced therefrom and which also extends towards the outlet of the nozzle but not below the outlet of the nozzle, said annular chamber only permitting the escape of gas from the chamber in the direction of the outlet and about the nozzle outer side wall, a tube extending into the annular chamber, and means for producing a puff of compressed gas coupled to said tube in order to produce a symmetrical puff of gas flow between the outer said wall of the nozzle and the inner side wall of the hollow cylindrical member to effect removal of liquid adhereing to the nozzle outlet.

4. The device according to claim 3 in which the storage means, comprises a syringe, the means for dispensing comprises a syringe plunger and the nozzle comprises a needle, and in which the cylindrical member surrounds and is supported by a portion of the syringe.

5. A device according to claim 4 in which the needle extends past the end of the hollow cylindrical member.

6. A device according to claim 5 in which a valve is provided in the tube to only permit the flow of gas into the annular chamber.

7. A device according to claim 3 in which a hand operable bulb is coupled to the tube.

8. A device according to claim 3 in which the cylindrical member surrounds and is supported by a portion of the nozzle.

9. A device according to claim 8 in which the nozzle extends past the end of the hollow cylindrical member.

10. A device according to claim 9 in which a valve is provided in the tube to only permit the flow of gas into the annular chamber.

11. A device according to claim 3 in which the nozzle includes a chisel edge at the end thereof about the outlet.