Abstract:
A pipette including a cylinder part having a cylinder and a tip part, which includes a tip channel connected to the cylinder and a movable piston tightly fit within the cylinder for aspirating liquid into and removing liquid from the tip container attached to the cylinder. In the pipette at least the tip part is made of an elastic material, such as rubber. The tip container can thus be easily and reliably fixed to and removed from the tip container.

Description:
TECHNICAL FIELD 
     The invention relates to a pipette comprising at least one cylinder part comprising a cylinder and a movable piston disposed within the cylinder, and a tip part comprising a tip channel connected with the cylinder, a tip container being attached to the end of the tip channel for aspirating liquid with the aid of the piston. 
     TECHNICAL BACKGROUND 
     There are known pipettes comprising a tip part with circular cross-section connected to a cylinder part, a separate removable tip container, i.e. tip, being attached to the tip part. The tip is usually maintained tightly in position with the aid of a cone joint. In order to seal the tip, the tip part may comprise a separate seal, an O-ring seal, for instance, or the otherwise rigid tip part may be coated with an elastic rubber-like material. A method and a device for fixing a rigid tip part coated with an elastic rubber-like material to a tip have been disclosed in FI patent specification 84789. 
     Currently used pipettes have the drawback of the tip being either too tightly or too loosely attached to the pipette tip part. In tip parts equipped with separate seals, contamination of the joint areas between the seals and other parts also involves a problem. In multi-channel pipettes, there is the additional problem of insecure attachment of the tips or of irregular attachment of the tips as the tips are spaced by varying distances. Poor attachment of the tips may cause leakage, dosage errors or additional work in order to attach or detach the tips. 
     Currently used pipette tip parts have a typical hardness of approx. 78 Shore D. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to provide a pipette that overcomes the problems mentioned above. 
     The purpose of the invention is achieved by the means described in the independent claims. The dependent claims define some preferred embodiments of the invention. 
     The pipette of the invention is characterized in that at least the tip part of the cylinder part has been prepared so as to be flexible, and is made of an elastic material, such as rubber, that is softer than the tip. The tip is thus easy to attach and remove. As the tip part is being attached, it tends to be compressed to a smaller diameter, being tightly pressed against the tip. During removal, the tip is withdrawn by pulling it downwardly towards the tip part. The tip is easily detached from the tip part, because the cylinder part and the tip part stretch, resulting in a decrease of their diameter. Under these circumstances, the tip cannot be clogged as previously occurred in prior art pipettes. The invention is particularly useful in multi-channel pipettes, given the compensation of the distribution error of the channels or a row of pipettes to be attached with tips. In accordance with the invention, problems caused by thermal expansion can also be reduced. 
     The invention also allows a pipette with a reduced number of separate parts to be achieved. 
     In multi-channel pipettes, the elastic tip part facilitates the gripping of tips from a tip rack. Owing to the elastic tip parts, the rack distribution may even be carried out with a slightly coarser tolerance. In addition, even inclined tips will settle more securely and at the same height in tip parts. 
     Measured on the Shore scale, the maximum hardness of the tip part material may be e.g. 60 shore D, such as 50 Shore D, especially 45 Shore D. The minimum hardness of the material may be e.g. 30 Shore A, such as 45 Shore A, especially 58 Shore A. 
     The ratio of the thickness of the tip part wall to the diameter of the tip part may be e.g. 1/10-1/3, such as 1/6-1/4. The diameter of the tip part may be e.g. 1-10 mm, such as 2-8 mm, particularly 4-6 mm. 
     In a preferred embodiment of the invention, the cylinder part and the tip part are made of the same elastic material. 
     In a second preferred embodiment of the invention, the cylinder part and the tip part are made in one single piece. In this manner, the cylinder part and the tip part are of a simple design with an associated low cost to manufacture. In addition, as the tip part and the lower portion of the cylinder part have no separate seals with sealing grooves or similar contaminating folds or gaps, the tip part will remain cleaner and will also be easy to clean if necessary. 
     In a third preferred embodiment of the invention, the cylinder part comprises at least one seal that has been expanded by being pressed against the piston in order to seal the piston and the cylinder. By these means, a leak-proof cylinder is provided using a soft material and a straightforward and space-saving design is utilized. 
     In a fourth preferred embodiment of the invention, the cylinder part comprises in an upper portion thereof an O-ring seal pressed against a shoulder with a helical spring. The sealing between the cylinder and the piston is thus achieved in a simple and economical way using standard components. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the invention are described in greater detail below with reference to the accompanying drawings, in which 
         FIG. 1  shows the tip unit of a pipette of the invention in vertical cross-section, and 
         FIG. 2  shows a vertical cross-section parallel with the tip row of a multi-channel pipette made up of pipette units of  FIG. 1 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The pipette of  FIG. 1  has a cylinder part  1  comprising a cylinder  2 , a tip part  3  having a tip channel  4  connected with the cylinder, and a piston  5  sealed to the cylinder with an O-ring seal pressed against the shoulder  7  by a spring  8 . In addition, the pipette unit of  FIG. 1  also comprises a press ring  9  for the O-ring seal and a lock ring  10  for the spring. The upper end of the piston comprises a floating mechanism for fixing the piston, comprising a piston spring  11 , a piston flange  12  and a spring counter-plate  13 . The force of the spring  11  is greater than the frictional force between the O-ring seal and the piston. 
     In the pipette unit shown in  FIG. 1 , the cylinder part  1  and the tip part  3  are made in one piece of the same rubber-like material. The outer surface of the cylinder part has been shaped so as to match the shape of the tip to be fixed to a lower part thereof, and on the other hand, to adapt to the requirements of its inner components. A shoulder  15  is provided slightly above its central point. Above the shoulder, the outer diameter of the cylinder part is greater than the lower portion, as shown in  FIG. 1 . The cylinder  2  located within the cylinder part extends from the upper portion of the cylinder part to the upper portion of the tip part, where it is connected to the tip channel  4  of the tip part. At the upper portion of the cylinder part  1 , there is a part having a larger inner diameter for the sealing mechanism extending from the upper end of the cylinder part within the cylinder. The sealing mechanism consists of an O-ring seal  6  placed in the part having a larger inner diameter, the O-ring seal being expanded parallel to the cylinder radius by pressing it from above against a shoulder  7  provided underneath it by means of a press ring  9 . The force required for pressing is generated by a spring  8  placed within the part having a larger inner diameter in the upper portion of the cylinder. The spring is tensioned between the press ring  9  and the lock ring  10 . The lock ring is attached to the upper portion of the cylinder by means of a plate structure attached above the cylinder. 
     A reducing part  16  having more marked conicity than the tip part is provided between the cylinder part  1  and the tip part  3 . It is intended to act as a transitional zone between the cylinder part  1  and the tip part  3 , producing adequate thickness of the tip channel  4  connected to the lower end of the cylinder and thus adequate stiffness of the tip part relative  3  to the cylinder part  1 , so that the material elasticity will be distributed relatively evenly between the cylinder part  1  and the tip part  3  as the tip is being attached. Centering of the elasticity to the cylinder part  1  under the effect of a tip part  3  markedly stiffer than the cylinder part  1  would entail more difficult fitting of the tip and thus deteriorated tip tightness and adhesion. 
     The tip part  3  has been shaped appropriately conical for the tip fitting the pipette unit to be fixed in position as easily as possible at the fitting stage and removed at the detaching stage. A tip fitting into the pipette unit of  FIG. 1  has an upper portion that matches the shape of the tip part  3 . At its lower portion, the tip usually has an appropriately conically shaped end known per se. The tip may be made of e.g. plastic, glass or any other material that is sufficiently rigid and otherwise suitable for this purpose as such as tip material for the sample substance. 
       FIG. 2  shows a multi-channel pipette made up of the pipette units of  FIG. 1 . It comprises eight pipette units fixed to the same frame. In order to move the pistons of the pipette units simultaneously, one single horizontal plunger member  18  connected to the plunger arm  17  has been fitted in the pipette. The pipette units have been fitted at the same height and the same mutual distance. Using the multi-tip pipette of  FIG. 2 , the tips are fixed by inserting the tip parts e.g. into tips placed at the tip part intervals in a suitable mounting rack. The pipette usually comprises a tip removing mechanism, by means of which the tips fixed to the tip part can be pushed so as to be detached from the tip part. 
     The design and the materials of the different parts of the pipette unit of the invention may vary. Unlike the preferred embodiment described above, the pipette unit may also comprise a cylinder part made of any rigid material, to which a tip part made of an elastic material has been connected. Unlike the design of  FIG. 1 , the cylinder part  1  and the tip part  3  may further be made of separate pieces, yet both made of a suitable elastic material, which may or may not be the same. The cylinder part  1  an the tip part  3  may have a shape different from that of  FIG. 1 , for instance shaped in some other way to match the shape of the inner surface of the conical tip. The size and tightness of the cylinder, the tip channel and the piston may also be carried out in many different ways. They can be determined as desired, for instance on the basis of the design and the material of the cylinder and the piston, and of the substances to be handled with the pipette. A support structure of a harder material, such as a ring, may be attached to a tip part made of an elastic material. 
     The pipette unit of the invention may be provided in a single-tip pipette, or a multichannel as shown in  FIG. 2  can be formed of pipette units. The remaining components of a pipette formed of pipette units may be carried out in any manner suitable for the pipette of the invention. The pipette may also be electrically driven and/or equipped with electric measuring devices.