Measuring and testing – Volumetric content measuring
Reexamination Certificate
2000-09-13
2003-04-29
Raevis, Robert (Department: 2856)
Measuring and testing
Volumetric content measuring
Reexamination Certificate
active
06553824
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is the National Stage of international application No. PCT/EP99/01640, filed Mar. 12, 1999, which claims priority to German application No. 19810997.0, filed Mar. 13, 1998.
The invention relates to a method for determining a volume of liquid, which is drawn from a vessel by means of a pipette or delivered from a pipette into a vessel, respectively.
Various apparatuses are known which permit the detection of volumes of liquid by determining the level of a calibrated vessel. This may be achieved, for example, by emitting ultrasonic, which is reflected by the surface of the liquid. By determining the period of time elapsed between emitting and receiving the reflected waves the level can be determined. Moreover, conductivity measurements are used for level determination, wherein a probe undergoes a change in conductivity from the point of time of being immersed into a liquid. The prerequisite for applicability of said method being a minimum conductivity of the liquid, the level of which is to be determined.
Within the scope of the present invention a capacity is measured for determining the volume of liquid. In this case a metal surface serves as a first pole, which metal surface is in contact with the vessel, in which the volume of liquid to be detected is located. The second pole is provided by a detector tip, which is moved slowly from above towards the liquid. As is known, the capacity between the two poles is determined by the distance of the same as well as by the medium being located in between. In the moment in which the detector tip is immersed into the liquid, a sudden change of the dielectric constant of the medium being located between the poles takes place, since exactly from this point of time air is excluded from between the two poles. In known automatic pipetting machines the presence of liquids in vessels on the working surface is verified thereby, wherein a too deep immersion of the pipetting needle is prevented.
The above methods for detecting liquids are known from the prior art. The present invention can in general be performed with various of said methods and is thus not limited to the same.
In performing automatic methods for pipetting, a plurality of causes may lead to pipetting errors, such as for example
obstructions of pipetting tips,
too early response of the liquid detection by faulty alignment,
leakage in the hose system,
leakage in the dilutors.
All causes lead to the fact that a lesser volume of liquid than the actually desired one or, in the extreme case, even no liquid at all is drawn from the vessel into the pipette or is delivered from the pipette into a vessel, respectively. Especially with liquids having a very high steam pressure a response of the liquid detection may be caused already in the gas volume above the liquid, due to the high concentrations prevailing therein.
The drawbacks of the known methods reside in the fact that, during the automatic pipetting process, it is not checked whether liquid has actually been drawn off or delivered, respectively, during the pipetting step and whether the maximum deviation of the pipetted volume from the desired volume is within a predetermined tolerance limit. Pipetting errors are thus not recognized and the attention of the user cannot be drawn to this fact.
The present invention is thus based on the object of providing a method for determining pipetting errors in automatic pipetting processes.
This object is achieved by the invention by the methods specified in independent patent claims 1, 2 and 3 as well as by the apparatuses specified in independent patent claims 8, 9 and 10. Further advantageous details, aspects and embodiments of the invention may be gathered from the dependent patent claims, the description, the figures and the examples.
The above-mentioned object is achieved according to the invention, for example, by a method for determining a volume of liquid, which is drawn from a vessel by means of a pipette, wherein the method comprises the following steps a) through f). As the first step (step a)) the volume of liquid contained in a vessel V
1a
is determined by a detector means and the value is stored in a computing unit. Then (step b)) a volume of liquid V
1act
is drawn into a pipette and, subsequent thereto, the volume of liquid contained in the vessel V
1e
is determined again by a detector means and stored in a computing unit (step c)). Thereafter the calculation of the volume of liquid actually drawn off V
1act
is conducted by the computing unit in accordance with the equation V
1a
−V
1e
=V
1act
(step d)) Subsequent thereto the difference between the volume of liquid actually drawn off V
1act
and a volume of liquid predetermined to be drawn off V
1targ
is calculated by the computing unit in accordance with the equation |V
1act
−V
1targ
|=V
1diff
(step e) Then a comparison of the difference V
1diff
with a predetermined volume of liquid &egr;
1
is conducted again by the computing unit and an error message is displayed in case V
1diff
>&egr;
1
(step f))
Furthermore, the invention relates to a method for determining a volume of liquid, which is delivered from a pipette into a vessel, wherein the method comprises the following steps a′) through f′). As the first step (step a′)) the volume of liquid contained in a vessel V
2a
is determined by a detector means and the value is stored in a computing unit. Then (step b′)) a volume of liquid V
2act
is delivered from a pipette into the vessel and, subsequent thereto, the volume of liquid contained in the vessel V
2e
is determined again by a detector means and stored in a computing unit (step c′)). Thereafter the calculation of the volume of liquid actually delivered V
2act
is conducted by the computing unit in accordance with the equation V
2e
−V
2a
=V
2act
(step d)). Subsequent thereto the difference between the volume of liquid actually delivered V
2act
and a volume of liquid predetermined to be delivered V
2targ
is calculated by the computing unit in accordance with the equation |V
2act
−V
2targ
|=V
2diff
(step e′)). Then a comparison of the difference V
2diff
with a predetermined volume of liquid &egr;
2
is conducted again by the computing unit and an error message is displayed in case V
2diff
>&egr;
2
.
Moreover, the present invention relates to a method for determining a volume of liquid, which is transferred from a first vessel to a second vessel by means of a pipette. In this method according to the invention firstly the above-mentioned steps a) through f) are performed in order to determine the volume of liquid drawn from the first vessel into the pipette, then the pipette is moved from the first vessel to the second vessel and, subsequent thereto, the above-mentioned steps a′) through f′) are performed in order to determine the volume of liquid delivered from the pipette into the second vessel. The volume of liquid drawn off from the first vessel may differ from the volume of liquid delivered to the second vessel.
Furthermore, the invention relates to an apparatus for determining a volume of liquid, which is drawn from a vessel by means of a pipette, wherein the apparatus comprises a memory means for storing numerical values, means for determining a volume of liquid contained in the vessel V
1a
, means for drawing a volume of liquid V
1act
into a pipette, means for determining the volume of liquid contained in the vessel V
1e
, means for calculating the volume of liquid actually drawn off V
1act
in accordance with the equation V
1a
−V
1e
=V
1act
, means for calculating the difference between the volume of liquid actually drawn off V
1act
and a volume of liquid predetermined to be drawn off V
1targ
in accordance with the equation |V
1act
−V
1targ
|=V
1diff
, means for comparing the difference V
1diff
with a predetermined volume of liquid &egr;
1
and means for displaying an error
Qiagen GmbH
Raevis Robert
Yankwich Leon R.
LandOfFree
Method for determining pipetted volumes of liquid does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for determining pipetted volumes of liquid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for determining pipetted volumes of liquid will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3110256