Apparatus for pipetting and adding a liquid

BACKGROUND OF THE INVENTION

The present invention relates to an arrangement in a pump for p Ip etting a liquid sample and for adding a liquid reagent.

The invention is especially adapted for use in micropipetting, i.e. when the pipetting takes place with volumes smaller than 15 microliters, but it is not restricted to this application and can be used with advantage when it is a question of pipetting very accurately determined volumes.

Particularly in micropipetting with the addition of a liquid reagent it has proved difficult to achieve a constant pipetted volume of liquid sample from one time to the next, which is partly due to variations in volume of the flexible tube serving for applying liquid reagent to the pipette. For example, the elasticity of the tube and the variations in the time required for it to return to its original volume after a stroke of the pump leads to important variations in the overall volume owing to temperature variations, hysteresis in the material of the tube, and movement of the tube. These variations can be as high as several percent.

SUMMARY OF THE INVENTION

These difficulties are avoided according to the present invention by means of a pump comprising a pump cylinder, a pump piston insertable in said pump cylinder, and actuation means for said pump piston, a tubular cannula connected to said pump cylinder for drawing up a liquid sample, a conduit for supplying liquid reagent to said pump cylinder, said conduit having provided therein a valve means adapted to be actuated to its open position when the pump piston reaches a position corresponding to an emptying of the pump cylinder.

The valve means provided in the conduit preferably comprises a valve element held in closed position by spring means. Opening of the valve means may be achieved by employing as the piston pump one having the form of a rod-shaped displacement piston and adapting the piston rod to lift the valve element from its closed position when the pump rod reaches the position corresponding to an emptying of the pump cylinder.

The actuating means for the pump piston is preferably composed of an actuating piston slidably disposed and springloaded in a housing, the actuating piston being connected to the pump piston, and means for supplying compressed air to drive the actuating piston.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described below with reference to the attached drawing showing an embodiment of the pipetting apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus for the invention shown in the FIGURE is adapted to transfer liquid sample from a test tube in a series 1 of test tubes to another test tube in another series 2 of test tubes and for supplying liquid reagent to the quantity of liquid sample thus transferred. For instance, a certain quantity of liquid sample is to be transferred from the test tube 3 of the first series to the test tube 4 of the second series and liquid reagent is to be supplied from a container 5. To this end, there is provided in the apparatus a tubular cannula 6 which can be moved in a path indicated by the dotted line 7 in a manner known per se, as shown on the drawing. Cannula 6 is connected to a pump comprising a cylinder 8 with a pump piston 9 insertable therein and preferably having the form of a rodshaped displacement piston. The pump piston is connected to an actuating piston 10 provided in a cylinder 11. A spring 12 urges the actuating piston 10 towards an end position in cylinder 11. Actuating piston 10 can be brought into the other terminal position against the action of spring 12 by means of compressed air supplied from a compressed air source 13. The supply of compressed air to cylinder 11 is controlled by a valve means 14 which responds to a common control means IS provided for the apparatus. The stroke of actuating piston 10 can be adjusted by means of a rod 16 which can be screwed to a variable degree into an end wall of cylinder 11. The position of rod 16 can be fixed with a lock nut 17 which may also serve as a sealing between rod 16 and the end wall of the cylinder.

The compressed air acts on one side of actuating piston 10 and on the other side thereof a constant pressure is maintained through an aperture 18 provided in the wall of the cylinder.

The pump cylinder 8 communicates directly with the tubular cannula 6 and is also connected through a valve 19 with a conduit 20 for supplying liquid reagent from container 5. This conduit also has provided in it a pump 21 for the liquid reagent and a valve means 22 which is controlled by control means 15.

The valve member 23 of the valve 19 is held by a spring 24 in seated position and can be unseated against the action of spring 24 by the pump piston 9 pushing against valve member 23 in the position of the pump piston corresponding to a complete emptying of the pump cylinder.

The operation of the apparatus will now be described. First, however, it should be noted that the test tubes of series 1 and 2 are not drawn to the same scale as the pump which has been enlarged on the drawing in the interest of clarity. Also, the entire unit comprising pump 8, 9 and actuating pump 10, 11 is adapted for movement together with tubular cannula 6 so that the latter can be attached to pump 8, 9 in a fixed manner. On the other hand, flexible portions 25 are provided in the connection between valve 14 and actuating cylinder 11 as well as between valve 22 and valve 19.

With the pump piston 9 in the uppermost position with reference to the drawing, cannula 6 is lowered into test tube 3 after which valve means 14 is actuated by control means 15 to a position in which the compressed air does not act on actuating piston 10. The latter is then brought by spring 12 to the lowermost position with reference to the drawing as defined by rod 16. This causes a predetermined quantity of liquid sample to be drawn into cannula 6 corresponding to the displacement of piston 9, and during this movement of the piston valve 19 remains closed whereby the quantity of liquid sample that is drawn into cannula 6 is determined exclusively by the displacement of the piston in cylinder 8. Cannula 6 is then moved along the path shown in dotted lines to test tube 4 and valve means 14 is actuated by control means 15 so as to cause compressed air again to be supplied to the pump. Actuating piston 10 with pump piston 9 are then displaced against the action of spring 12 to the uppermost position and the quantity of liquid sample drawn into cannula 6 is emptied into test tube 4. When the pump piston 9 has reached the topmost position, with reference to the drawing, it reached valve member 23 and causes it to be unseated. Simultaneously, or after this, control means 15 actuates the other valve means 22 causing the connection between liquid reagent pump 21 and conduit 20 to be established. Pump 21 is now made to supply a predetermined quantity of liquid reagent which flows through conduit 20 and valve 19 down into cylinder 8 and tubular cannula 6. Simultaneously, with the supply of liquid reagent to the liquid sample in test tube 4, the interior of cannula 6 is rinsed from possibly remaining traces of liquid sample. Cannula 6 is then transferred to the other test tube in series 1 after which the sequence of events just described is repeated.

To reduce still further the danger of an undesired transfer of liquid sample from one sample to another, it is possible, simultaneously with the supply of liquid reagent in the manner referred to above, to cause a rinsing of the exterior of cannula 6 by supplying liquid reagent via a branch conduit 26 of conduit 20 to an annular nozzle 27 placed around cannula 6. By suitable dimensioning of branch conduit 27 relative to the path leading through cannula 6, it can be achieved that a suitable quantity of liquid reagent causes the desired rinsing of the exterior of cannula 6.

3,607,094

In the embodiment of the invention shown, movement of actuating piston 10 in one sense is limited and adjusted by means of rod 16. Movement in the other sense is limited by means of the interior surface of the terminal wall of the piston contacting the free end of the tube 28 which is screwed into the upper end wall of cylinder 11. The length of tube 28 is selected so as to cause pump piston 9 to unseat valve member 23 at the precise moment when actuating piston 10 is stopped by tube 28. As indicated in the drawing, the upper end of the tube is arranged to hold a sealing O-ring in contact with pump piston 9.