DE1598123A1 - Automatic pipette - Google Patents

Description

Automatic pipette The invention relates to an automatic pipette Pipette with a housing in which a piston can be displaced. In many cases it is necessary to pipette an exact amount of liquid, e.g. in microchemistry or in other biological or chemical fields. When determining the prothrombin and clotting time become standardized and stabilized chemical reagents in glasses to a certain temperature, usually that of the human body, heated, whereby it is essential for exact timing that the amount of used Reagents is strictly observed.

Control plasma, likewise in a certain quantity, is then added to the reagents admitted. The beginning of the Coagulation detected.

The same procedure is then followed with a certain amount of the plasma performed by the patient. The prothrombin times are read and recorded. In order to achieve accurate and repeatable results it is therefore necessary to a certain amount of pipetting to be adhered to exactly and the beginning of the reaction if possible precisely to be determined.

The invention has set itself the task of creating a pipette, which allows precise dosing of changing amounts of liquid without the Activity must be carried out by highly qualified specialists. to the solution To this end, a pipette is proposed according to the invention, which is characterized in that is that the piston is rotatable relative to the housing and that stops in the housing for the piston are provided with which the piston depending on its angular position alternatively cooperates with respect to the housing to reduce the piston stroke and thus the Limit the amount of liquid expelled. In this way it is always possible with To adhere to certain pipetting quantities with a great accuracy, sometimes to change the dosage only rotates the piston in a certain way with respect to the housing needs to become.

In order to rule out any possibility of Fetlors practicing pipetting, are provided in the housing guides that allow rotation of the piston only in the fully pulled out, allow an unintentional change from a dosage to another during the insertion of the piston is excluded. Guide ribs, which are also provided in the housing, serve the same purpose and only allow the piston to be pushed in if it is in a defined, a certain dosage corresponding angular position relative to the housing. The piston can be provided with a side flange that when pushed in of the piston is guided between the guide rails and with the piston stroke limiting attacks cooperates.

To the user the recognition of the angular position of the piston, so To facilitate the set dosage, the piston with the corresponding indicator marks be provided.

As mentioned earlier, when pipetting, in many cases it is necessary to To precisely record the beginning of the reaction, so far has been used for this purpose at the moment the expulsion of the liquid operated a stopwatch and stopped the reaction time.

However, this type of timing is rather imprecise because it depends on the skills of the laboratory technician. To remedy this evil are According to the invention, electrical contacts are provided in the housing, which give a timepiece included circuit and which are actuated by the piston when this is in or near one of its inner end positions. In this way inevitably becomes an electrical one the moment the liquid is expelled Generates a signal that starts the time measurement. There the hub of the Piston can take different values, stops are provided in the piston, which, depending on the angular position of the piston, go over the housing as an alternative the contacts cooperate to achieve that only towards the end of the Piston movement generates the electrical signal to prevent the contacts are operated unintentionally, there is a manually operated safety switch in the housing forward. The contacts and the safety switch are preferably in one laterally housed from the housing extending handle.

In order to facilitate the disposal of the pipette and also by inexperienced To enable Pexsonen, the pipette is preferably with an exchangeable one Pipettonspitze provided, the volume of which is greater than the stroke volume of the piston. This ensures that there is always a cushion of air between the liquid in dor pipette tip and the cylinder space of the pipette, which means contamination the pipette is avoided.

To facilitate handling of the pipette according to the invention is it is advantageous to provide a coupling to attach the pipette tip to the housing, which is designed in such a way that the lengthways of the pipestip are aligned lengthways of the housing includes an acute angle, between the cooperating Areas of the coupling and the housing means are provided which have a predetermined Ensure the position of the coupling relative to the hatch.

An exemplary embodiment of the invention is described below with reference to FIG Drawings explained in more detail. 1 shows a perspective view of FIG automatic pipette in connection with an electric timer, Fig. 2 a enlarged longitudinal section along line 2-2 in Fig. 1, Fig. 3 a Section similar to FIG. 2, with the safety switch closed and the piston is pressed in to expel liquid.

Fig. 4 is a cross section along line 4-4 in Fig. 2, Fig. 3 is an enlarged Partial view of the pipette housing in the direction of the arrows 3-5 in Fig. 3, Fig. 6 iene View of the pipette from above, with part of the housing broken away, Fig 7 shows a section along line 7-7 in FIG.

8 shows a view of the piston from the rear, and FIG. 9 shows a longitudinal section through the pipette tip on an enlarged scale.

The pipette, generally designated 20, has a piston 22, which is arranged linearly displaceable in a housing 24, from which a hollow Handle 26 extends, which is closed at the rear by a cover 28. That front end of housing 24 contains an inwardly extending cylinder 30 and a forwardly extending slotted conical projection 32, that with one of individual segments separated from one another by slots 40 @ formed snap bead 34 is provided. Dig inner surface 36 of protrusion 32 is separated from the bore 38 of the cylinder 30 by a shoulder 40. Internally of the housing 24 two longitudinal guide ribs 42 and 44 are provided, which prevent the piston 22 from being pushed in if the piston is not properly in a position corresponding to a dosage is rotated.

On the inner side walls of the housing 24 there are two guide rails 46 and 48 (Fig. 7) attached, between which stops 50 and 32 are provided. The stops 50 and 32 limit the stroke of the piston 22 according to the desired dosage. The stops 52 are slightly longer than the stops 50, so that the piston 22 in the position 1 in which it interacts with the stops 52 has a small stroke and thus pushes out a smaller amount of liquid.

The handle 26 is provided with two threaded connectors 54 and 56 which serve to accommodate the fastening screws 58 and 60 of the cover 28. the Nozzles 54 and 56 are also used together with other nozzles 62 and 64 for holding of electrical contacts 66,68 and 70. These contacts are made by ribs 72 (Fig.7) held in place on both sides of the inner surface of the handle 26 and guided. The lower end of the handle 26 is provided with an opening 74 through which the contact pin 76 of a plug 78 'can be inserted to the electrical Establish connection between the contacts in the handle 26 and the timer 80.

The lid 28 is provided with a rectangular opening 86 in which a switch 88 is vertically displaceable. This switch 88 has a from the handle 26 protruding finger support surface 90 and an inner sloping surface 92, which cooperates with the normally open switch contact 70.

The inclined surface 92 is with two beindlichen at a distance from each other Grooves 94 and 96 are provided, the open position and the closed position of the contact 7 define. In the closed position, contact 70 is in contact with contact 68, which in turn is normally open to the third contact 66. The contacts 66 and 68 are closed when the piston 22 is pushed forward (see Fig. 3). The Dkkel 28 is provided with a circular opening 98 through which the piston 22 extends through and serves as a guide for the piston 22. The end surface 100 serves as a stop for the backward movement of the piston 22 and has a recess 102 into which the ends of the contacts 66 and 68 protrude.

-6- The upper end of the Abschiußdeckels 28 is with a finger grip 104 provided which the actuation of the piston 22 eases tert. That The lower end of the handle 104 rests on an upwardly extending nose 106 of the housing 24.

The rear end of the piston 2 is provided with a push button 1b8. of the brands. who give what a dosage when pressing the Piston 22 is reached. The markings exist in the exemplary embodiment of a groove 110 and a double groove 112 arranged diametrically to it. If the double groove 1: 2 at the top (see Fig. 8), when the piston 22 is pushed in fully, 0.2 cm3 displaced, while in the position of the piston 22 in which the groove 110 is at the top is, 0R1 cm3 to be displaced. The front end of the piston 22 is provided with a radial riansch 113 (FIG. 7), which has a finished set 114 on the side. This Extension 114 works with guide ribs 42, 44 and guide rails 46 and 48, respectively together and comes into contact with the ass punches 50 or 52. depending on which one Position of the piston 22 is rotated. The guide rails 46 and 48 prevent that the piston 22 can be rotated1 when it is already pushed in.

The piston 22 is provided with guards 116 on opposite sides and 118 (Fig. 2) which are of different lengths and in which the ends of contacts 66168 protrude.

When the piston 22 is in its corresponding end position dio contacts 66 and 68 through the end face of the slot 116 or 118 concerned closed, thereby the timer 80 is switched on.

A rod 120 extends from the front end of the piston 22. which has a bifurcation 122 at its inner end which extends into the bore 124 the piston 22 is pushed in.

Piston 22 and rod 120 can, however, also consist of one piece. The outer end of the rod 120 has a circumferential groove for receiving an O-ring 126 on, which is in a tube 128 slide some of them into the The cylinder bore 38 is pushed in. The piston 22 is inserted together with the rod 120 pressed by a compression spring 130 to the right in the drawing. The spring 130 surrounds the cylinder 30 and is supported on the one hand on the front end of the housing 24 and on the other hand from the radial flange 113 of the piston 22.

A coupling part 132 is releasable at the front end. of the hanger 2 attached and is used to attach a replaceable pipette tip 134 to the housing 24. The coupling part 132 is provided with a bore 136 which the front end of the Tube 128 receives. A bore 138 of smaller diameter extends from the bore 136 from, whereby a shoulder 140 is formed on which the tube 128 is supported. The pipe 128 can also be connected to the coupling part t32 by welding.

The coupling part 132 is provided with a conical inner surface 142, which cooperates with the outer surface of the conical extension 32, In de @ surface 142 is a circumferential groove 144 is provided with the snap bead 34 on the front The end of the extension 32 cooperates. When the coupling part 132 over the fortsais 32 is pushed, the conical inner surface 142 pushes the bead segments 34 radially inwards until they can snap into the circumferential groove 144, the correct position of the coupling part 132 with respect to the housing 24 is achieved by the tongue and groove arrangement 146 (Fig. 5) is reached.

The front end of the coupling part 132 points diagonally downwards extending conical opening 148, which with the bore 138 in connection stands. The correspondingly shaped fode 150 of the pipette tip is inserted into this opening 148 134 pushed in and held by friction. The pipette tip 134 is designed so that that as far as possible no drop occurs, as can be seen from FIG. 9 the pipette tip 134 has a relatively small conical channel 152 Diameters on. The front end 154 of the pipette tip is also tapered, whereby the Tendency to droplet formation is reduced. The relatively great length of the Pipette tip in relation to its inner diameter not only gives the necessary one Capacity for the pipette, but also allows for a very gradual increase in size of the diameter from the smallest to the largest diameter, whereby the tendency of the Fluid swinging at the tip while pushing it out is limited becomes the more acute the angle at the end 154 and the smaller the outer surface is at the end of the tip, the lower the tendency for droplets to form on it Job.

Ribs 156 are attached to the outside of the pipette tip 134, Un screwing and pushing the tip into the opening 148 of the coupling point 132 to facilitate. To avoid fluid loss when the fluid being sucked into the channel 152 of the tip 134 is the mouth of the channel 152 as small as possible. This creates a negative pressure above the liquid column when it is sucked in in the pipette tip that holds the liquid in the channel 152. It also bears the surface tension of the liquid contributes to the liquidity being. the Tip remains. For this reason, the trapped air should be released when pushing out like a piston acts on the liquid, cannot escape.

The volume of the enal 152 is greater than the stroke volume of the piston 22, whereby it is achieved that the pipetting liquid never enters the pipette housing can occur. This avoids any contamination of the pipette housing.

A successfully used pipette tip has the following dimensions: Total length 8.45 omi wall thickness 0.63 mm; Bevelling at the front end 600t inner Diameter at the front end 1 mm; inner diameter at the rear end 3.5 mm; Volume with filling up to 6.3 om from the front end: 0.203 Although a number of materials for making the various parts of the invention Pipette can be used, are particularly good results with the following materials obtained: Metal was used for the pipe 128 and the coupling part 132. The pipette tip 134 was molded from either styrene or polyethylene, however other non-wettable transparent plastics can also be used. For the housing 24 and the integral handle 26, the cover 28, the piston 22 and the other parts became a casting resin. e.g. Delrin from DuPont used. this material is very dimensionally stable, has relatively great fatigue strength and very low thermal expansion.

The pipette is handled as follows: Assume that the Pipette 20 is coupled to a timer 80 by means of plug 76. The piston 22 is relative to the housing 24 in the position corresponding to the desired dosage The switch 88 is in its off position. A new tip 134 is inserted into the coupling part 132. The piston 22 is now pushed in and the tip 134 is immersed in the liquid to be pipetted. In case of For prothrombin, this liquid would be plasma. After the top 34 is immersed in the liquid, the piston 22 is withdrawn to the Desired plasma tightness to suck into the channel 152 of the tip 134. After completion of what is sucked in, the extension 114 of the flange 113 rests against the stop 100 is a precise volume of plasma in the Spitre 134, with between the front End of the piston rod 120 and the plasma is a column of air that is together with the surface tension of the liquid holds the plasma in the pipette tip 134. The tip 134 is then withdrawn from the plasma and the load 88 into the On position shifted in which the contact 70 with the contact 68 in contact comes. By pushing the piston 22 forward, the exact amount of plasma is now in a reaction vessel pushed out.

The trapped air acts on the plasma in front of the O-ring 126 in the tip 134 and pushes the plasma out through the tapered end 154. To The end of the forward stroke of the piston 22 is effected depending on the selected dosing quantity the end of the slot 116 or 118 that the contacts 66 and 68 close, whereby the electrical circuit is closed to the timer 80, which is switched on by is about the time until the formation of the first flakes and thus the prothrombin time to determine.

The accuracy of the pipette according to the invention exceeds the capability Any average lab technician using standard glass pipettes. Pipettes according to the invention have an average absolute accuracy of more than 98% of the drawn volume The tolerance between the individual pipettes is in the Of the order of # 2%. The simultaneous shadowing of a timepiece is guaranteed an accurate determination of the response time and avoids all influences that go through Operation of the timer by various laboratory assistants could occur completely the end. Also all cleaning problems are eliminated because the pipetting liquid never enters the housing of the pipette and the pipette tips are interchangeable are # patent claims #

Claims (12)

P a t e n t a n s p r ü c h e 1. Automatic pipette with a housing, in which a piston is displaceable, characterized. that the piston (22) is rotatable with respect to the housing (24) and that stops (50.52) in the housing (24) for the piston (22) are provided with which the piston (22) depending on its angular position alternatively cooperates with respect to the housing (24) in order to limit the piston stroke. 2. Pipette according to claim 1, characterized in that in the housing (24) guide rails (46, 48) are provided which enable rotation of the piston (22) Allow only when fully pulled out. 3. Pipette nsch claim 1 or 2, characterized in that im Housing (24) guide ribs (42, 44) are provided, which push in the piston (22) only allow if this is in a defined angular position opposite the housing (24) is located. 4, pipette according to one of claims 1 to 3, characterized in that that the piston (22) has a Seitenlibhen flange (114) that when pushed in of the Kolsen (22) between. the guide rails (46 or 48) is guided and with the stops (50 or 523) cooperates. 5. Pipette according to one of the preceding claims, characterized in that that the piston (22) indicator marks (110, 112) for its angular position opposite the housing (24). 6 pipette according to one of the preceding claims, characterized by a spring (130) that moves the piston (22) into its outer end position seeks. 7. Pipette according to one of the preceding claims, characterized in that that in the housing (24) electrical contacts (66, 68) are ovrgeschen that one Belong the timer (80) containing circuit and operated by the piston (22) if it is located in or near one of the inner discoveries. 8. Piepttei according to claim 7, characterized in that the piston (22) has stops (116, 118) which, depending on the angular position of the piston (22) Geenüberwieken the housing (24) alternatively with the contacts (66,68) together. 9. Fipetto according to claim 7 or 8, characterized in that im Housing (24) a manually operated safety switch (88) is provided which unintentional actuation of the Kentakts (66, 68) is prevented. 10 ,. Pipette according to Claims 7 to 9, characterized in that that laterally from the housing (24), a handle (26) extends, in which the contacts (66,68) and the safety switch (88) are arranged. 11. Pipettes according to one of the preceding claims, marked by a replaceable pipette tip (134), the volume of which is greater than that Stroke volume of the piston (22), 12. Pipette according to claim 12, characterized in that that for fastening the pipette head (134) to the housing (24) a coupling (132) is formed so that the longitudinal axis of the pipette tip (134) forms an acute angle with the length axis of the housing (24), wherein means between the cooperating surfaces of the coupling (132) and the housing (24) (146) are provided which a predetermined position of the coupling (132) relatively aum Guarantee housing (24).