Measuring and testing – Sampler – sample handling – etc. – Capture device
Reexamination Certificate
2002-07-18
2004-07-06
Williams, Hezron (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Capture device
C422S105000
Reexamination Certificate
active
06758106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a liquid proportioning method and an apparatus for implementing the method.
2. Field of the Invention
Pipettes and other proportioning systems which operate according to the air cushion principle have been known already. They involve displacing an air column to draw the liquid into a pipette tip and to expel it therefrom. The displacement of the air column is performed by a piston in a cylinder. In hand-operated pipettes, the piston is displaced by means of an actuator button against the action of a restoring spring. In pipettes the proportioning volume of which is adjustable, an adjustable stop exists to limit the piston stroke. Adjustment is effected by means of a rotary toothed wheel which acts on the stop via a gearing with the proportioning volume adjusted being read by means of a counter.
In the known hand-operated pipettes, it is time-consuming and cumbersome to adjust the proportioning volume. The gearing to shift the stop has been designed so as to effect the desired precision of adjustment. In the most unfavorable case, this gearing has to be shifted through the entire setting range. Moreover, it is unfavorable ergonomically that the displacement of the piston stop changes the stroke of the actuation button for the piston. It is particularly unfavorable that if there are small proportioning volumes short actuation strokes have to be performed at a comparatively high expenditure of force against the action of the restoring spring.
Accordingly, it is the object of the invention to provide a method for the proportioning of liquids and an apparatus for the proportioning of liquids that has more favourable handling attributes.
SUMMARY OF THE INVENTION
This object is attained by a method of the proportioning of liquids using a chamber for a gas and a reception volume connectable thereto for a liquid with an aperture to the environment, in which:
a desired volume is predetermined for the liquid to be taken up by the reception volume,
a chamber negative pressure is determined which has to exist in the chamber to cause the desired liquid volume to be taken up in the reception volume after the aperture is dipped into the liquid and the chamber is connected to the reception volume,
the chamber negative pressure is produced in the chamber,
the reception volume dips its aperture into the liquid, and
the chamber is connected to the reception volume and the desired volume of the liquid is taken up in the reception volume.
In the inventive method, the proportioning volume is not adjusted by a variation to a piston stroke as is done in the state of the art. Rather, a chamber negative pressure is determined on the basis of a predetermined desired volume and is produced in a chamber the consequence of which, after the aperture is dipped into a liquid and the reception volume is connected to the chamber, is that accurately the desired volume ascends into the reception volume. The interconnection between the desired volume and the associated chamber negative pressure, for instance, may be determined for a liquid empirically (by experiments, in particular). However, it may also be calculated, for instance, by a calculation of the desired negative pressure which has to prevail in the reception volume above the liquid to maintain the desired volume of the liquid in the reception volume, and by a determination as to which chamber negative pressure initially has to be produced to accurately achieve the ascension of the volume desired for the liquid into the reception volume and the desired negative pressure above the liquid after the chamber is connected to the reception volume. Irrespective of the way the chamber negative pressure is determined in detail it is more readily realizable and facilitates handling very much to preset the desired volume and to determine and produce the chamber negative pressure than it is to adjust the proportioning and to actuate the piston in the state of the art.
It is preferred that the gas present in the chamber is air. The chamber negative pressure can be produced in different ways. According to an aspect of the method, a negative pressure produced in the chamber is measured and is matched to the chamber negative pressure following a comparison thereto.
Basically, it is possible to effect such matching to the chamber negative pressure by increasing the negative pressure in the chamber. According to an aspect, a negative pressure which exceeds the chamber negative pressure is initially produced in the chamber and the chamber negative pressure is then achieved by partial pressure compensation between the chamber and the environment. This allows to produce the chamber negative pressure in a particularly simple and precise manner.
According to another aspect, the negative pressure in the chamber is matched automatically to the chamber negative pressure.
It is not always necessary to dispense the liquid which was taken up to the outside from the reception volume, e.g. if it is intended to undergo an analysis or further methoding in the reception volume or a device having the reception volume. For delivery to the outside from the reception volume, according to an aspect, the liquid which was taken up is expelled from the aperture of the reception volume by applying a positive pressure to the reception volume. For instance, a volume desired for a liquid may be taken up in the reception volume from a reservoir and may be delivered into a reaction vessel from the reception volume.
According to an aspect, the desired volume is introduced manually. Since there is no forced coupling to a gearing to shift a piston stop the introduction of the desired volume is very easy in operation.
According to an aspect, the negative pressure and/or positive pressure is produced by means of a manually operable gas displacement device. This makes it possible to implement the method with a particularly low number of instruments.
According to an aspect, the gas displacement device, upon production of the negative pressure and/or positive pressure, is operated by a certain actuation distance independent on the choice made for the desired volume. This makes handling easier than do the variable ways of operation for the known adjustable pipettes.
Basically, it is possible to displace the liquid from the reception volume always at the same volume displacement rate whatever the desired volume is. If the volume displacement rate of the gas displacement device has been agreed with the maximum desired volume adapted to be preset and if a desired volume is preset which is smaller the result is that liquid will be expelled only via a short portion of the actuation distance of the gas displacement device. This, in turn, may cause errors in proportioning. For a “more delicate” delivery of liquid while utilizing the whole actuation distance, according to an aspect, the positive pressure applied to the reception volume is controlled so as to expel the liquid substantially through the entire actuation distance of the gas displacement device with no regard to the desired volume chosen. That part of the actuation distance which was passed through can be measured by a distance sensor here.
In any case, an excess stroke may be provided to make sure the liquid is virtually expelled completely from the reception volume.
An apparatus suited for use in implementing the method has
a chamber for a gas,
a reception volume for liquid that is connected to the chamber via a first valve means with an aperture to the environment,
a gas displacement device connected to the chamber via a second valve means,
a pressure sensor connected to the chamber,
input means for the desired volume and for controlling the reception and/or delivery of liquid, and
a control means which is connected to the input means, the pressure sensor, and the valve means to control the generation of the chamber negative pressure in the chamber and the reception of liquid into the reception volume and/or the delivery of liquid from the reception volume.
If gas requires to
Richter Jorg
Salje Gerhard
Von Beichmann Boris
Eppendorf AG
Garber Charles
Sidley Austin Brown & Wood LLP
Williams Hezron
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