[0001] The subject of the present invention is a pipette comprising a cylindrical handle
portion, a frame portion connected to same, in whose cylinder space a piston is fitted
for sucking liquid into, and removing liquid from, a tip connected to the lower end
of the frame portion and functioning as a liquid container, and that the piston is
provided with two piston rods fitted inside each other, each of them being at the
upper end provided with a knob, and that out of the said piston rods, the stroke of
the inner, secondary piston rod is longer than the stroke of the second piston rod,
surrounding the first one, and that the piston rods are prevented from rotating in
relation to the handle portion.
[0002] The invention is in particular concerned with a liquid dosage pipette, more specifically
with its adjustment for different volumes and with its calibration.
[0003] In the pipette in accordance with the invention the adjustment of the pipette for
different volumes and the calibration-can be performed by using the same adjustment
and calibration unit. It is particularly characteristic of the invention that the
calibration of the pipette can be performed from outside the pipette without opening
it and that the calibration unit moves along in such a unit .as transfers the movement
to the pipette piston or as is a part of the piston.
[0004] The pipette in accordance with the invention is mainly characterized in that around
the piston rod surrounding the secondary piston rod, a sleeve-shaped adjustment device
has been fitted by means of a threaded joint for the purpose of calibration of the
pipette, while the adjustment device is placed in the chamber space of the upper end
of the handle portion and is supported by means of shoulders against the support portion
of the handle portion and that the turning of the adjustement device in relation to
the piston rod so as to adjust or calibrate the pipette has been arranged as taking
place from outside the pipette by using the adjustment and calibration unit.. ;
[0005] By applying the invention described herein to pipettes of different types, e.g. to
adjustable or fixed-volume single-channel or multi-channel pipettes, remarkable advantages
are achieved as compared with such pipettes in which the calibration nut of the pipette
is fixed in the handle portion of the pipette or the calibration screw is placed inside
the pipette, in which case, every time that it is desired to calibrate the pipette,
the pipette must be opened.
[0006] The invention comes out more closely from the following description and from the
attached drawing, which shows an exemplifying embodiment of a pipette in accordance
with the invention as a side view in section.
[0007] In the pipette shown in Figure 1, a frame portion 2 is connected to a preferably
cylindrically shaped handle portion 1, inside which frame portion 2 a piston portion
3 moves and to which it is possible to connect a pipette_tip 4 functioning as a liquid
container. The sealing between the frame portion 2 and the piston 3 takes place by
means of an 0-ring 5, against which a spiral spring 7 presses by means of an 0-ring
support 6. A secondary piston rod 9 runs inside the piston rod 8, said secondary piston
rod 9 being connected to the adjustment unit 10 by means of a threaded joint. A flange
11, constituting a support for the spiral spring 7, presses the piston 3 against the
adjustment unit 10. The piston rod 8 is by means of a threaded joint connected with
the adjustment device 12, which is by means of shoulders supported against a support
and scale portion 13 connected to the handle portion 1.
[0008] Inside the handle portion 1 there are guides 14, which glide in the shaft 8 in guide
grooves 15 parallel to the longitudinal axis.
[0009] When pipetting is performed by means of the pipette shown in Fig. 1, the knob 16
in the upper part of the piston rod,8 is pressed, which knob transfers the movement
via the piston rod 8 and the adjustment; unit 10 located therein to the piston 3 by
the intermedaiate of the flange 11. During the step of filling of the pipette tip
4, the knob 16 is pressed the distance a to its lower position, and thereupon, while
the pipette tip 4 is in the liquid, the piston 3 is allowed to rise the distance a
to its upper position. When the pipette tip 4 is emptied, the knob 17 of the secondary
piston rod 9 is depressed, whereby the secondary piston rod 9 goes down a total of
the distances a and b. Here the total movement (a+b) is transferred by means of the
adjustment unit 10 to the piston by the intermediate of the flange 11, whereby the
emptying movement of the piston 3 is longer than its filling movement, which again
guarantees good emptying of the pipette tip 4 out of the liquid to be pipetted.
[0010] Below, some of the characteristics and advantages of the present invention will be
presented.
[0011] The pipette may be calibrated to a certain volume at the manufacturing stage by means
of an adjustment device'12to be operated from the outside of the pipette and connected
to the mobile piston rod 8. Moreover, the distance passed by the secondary piston
rod 9 inside the piston rod 8 can be adjusted by means of the adjustment unit 10.
[0012] .'When adjustment is performed by means of the adjustment device 12 by turning it
either clockwise or anticlockwise, turning of the piston rod 8 along with the unit
is prevented.by means of the guides 14 and guide grooves 15. These means also prevent
rotation of the piston rod 8 during pipetting.
[0013] The adjustment device=12 and the scale portion 13 can be provided with scales in
order to faciliate the calibration and/or to indicate a certain volume. Such scales
may, if necessary, be provided with markings so as to indicate a certain volume and/or
a certain mass for liquids of different specific gravities. The scales concerned may
also be used so that by their means a desired volume is adjusted for the pipette within
a certain volume range.
[0014] The invention'described here is also suitable for so-called reverse pipetting method,
wherein more liquid is taken into the pipette tip than is removed from it (Medical
Laboratory Technology, 31, 213, 1974). Then the filling of the pipette tip 4 takes
place so that the secondary knob 17 is depressed first into its lower position, whereby
the piston 3 goes down the total distance of a and b, and then liquid is sucked into
the tip 4 by allowing the piston 3 to pass to its upper position the distance a+b.
At the stage of emptying of the pipette tip 4 the knob 16 is depressed into its lower
position, whereby the piston 3 goes down the distance a. The volume of liquid corresponding
the distance a of the piston 3 is removed from the pipette tip 4. In many cases the
reverse pipetting method improves the precision and reproducibility of pipetting.
1. A pipette comprising a cylindrical handle portion (1), a frame portion (2) connected
to same, in whose cylinder space a piston (3) is fitted for sucking liquid into, and
removing liquid from, a tip (4) connected to the lower end of the frame portion (2)
and functioning as a liquid container, and that the piston (3) is provided with two
piston rods (8 and 9) fitted inside each other, each of them being at the upper end
provided with a knob (16 and 17), and that out of the said piston rods (8 and 9),
the stroke of the inner, secondary piston rod (9) is longer than the stroke of the
second piston rod (8), surrounding the first one, and that the piston rods are prevented
from rotating in-relation to the handle portion (1), characterized in that around
the piston rod (8) surrounding the secondary piston rod (9), a sleeve-shaped adjustment
device (12) has been fitted by means of a threaded joint for the purpose of calibration
of the pipette, while the adjustment device is placed in the chamber space of the
upper end of the handle portion (1) and is supported by means of shoulders against
the support portion (13) of the handle portion (1) and that the turning of the adjustment
device (12) in relation to the piston rod (8) so as to adjust or calibrate the pipette
has been arranged as taking place from outside the pipette by using the adjustment
and calibration unit.
