Pipetting device, fluid processing system and method for operating a fluid processing system

1. Pipetting device having a tube ( 1 ), wherein a liquid space of the tube ( 1 ) is at least partially filled with a working fluid ( 7 ) operatively connected at a first end of the tube ( 1 ) to a pressure-generating means, configured for aspirating or dispensing a sample liquid ( 4 ′) via an opening ( 3 ) provided at a second end of the tube ( 1 ), wherein the working fluid ( 7 ) and the sample liquid ( 4 ′) are electrically insulated from one another via an air gap ( 8 ), wherein a first electrode ( 5 ) is formed on the pipetting device, which, together with a second electrode ( 4 ′) formed by at least a part of the sample liquid ( 4 ′) accommodated in the tube, forms a measuring capacitor ( 6 ) operatively connected to a measuring unit which is configured, as a function of the capacitance of the measuring capacitor ( 6 ), to determine a volume of the aspirated or dispensed sample liquid ( 4 ′), the pipette device further comprising a first electrical contact ( 9 ′) which is electrically insulated from the first electrode ( 5 ) and the second electrode ( 4 ′) and which establishes an electrical connection with the working fluid ( 7 ), wherein the first electrical contact ( 9 ′) is electrically connected to the measuring unit via a low-impedance converter circuit, and

wherein the pipette device comprises a second electrical contact ( 9 ″) electrically insulated from the first electrode ( 5 ) and which establishes an electrical connection with the sample liquid ( 4 ′) upon aspiration or dispensing of the sample liquid ( 4 ′) such that at least a part of the sample liquid ( 4 ′) contained in the tube ( 1 ) forms the second electrode ( 4 ′) of the measuring capacitor ( 6 ), wherein the first electrode ( 5 ) is electrically connected to the measuring unit.

2. Pipetting device according to claim 1 , wherein the low-impedance converter circuit reduces parasitic capacitances caused by the working fluid ( 4 ′).

3. Pipetting device according to claim 1 , wherein the low-impedance converter circuit is provided with a high-impedance input and a low-impedance output.

4. Pipetting device according to claim 1 , wherein the first electrode ( 5 ) partially or completely covers the tube ( 1 ).

5. Pipetting device according to claim 1 , wherein the tube ( 1 ), at least in the region of the opening ( 3 ), comprises an electrically conductive material and forms the second electrical contact ( 9 ″), or alternatively comprises an electrically non-conductive material which is provided as dielectric of the measuring capacitor.

6. Pipetting device according to claim 1 , wherein the second electrical contact ( 9 ″) is established via a capacitive coupling via the sample liquid ( 4 ) which is loaded in a sample container ( 10 ) from which sample liquid is aspirated or into which sample liquid is dispensed.

7. Pipetting device according to claim 1 , wherein the second electrical contact ( 9 ″) is connected via a third switching element (S 9 ″) to the measuring unit, the low-impedance converter circuit or ground.

8. Pipetting device according to claim 7 , wherein further the first electrical contact ( 9 ′) and the first electrode ( 5 ) are each connected via a first switching element (S 9 ′) and a second switching element (S 5 ) to the measuring unit, the low-impedance converter circuit or ground, wherein physical effects which have a negative impact on the measurement results are substantially eliminated by switching the respective couplings between the first electrical contact ( 9 ′), the first electrode ( 5 ) and the second electrical contact ( 9 ″) to the measuring unit, the low-impedance converter circuit or ground, respectively.

9. Pipetting device according to claim 7 , wherein the second electrical contact ( 9 ″) is insulated from ground and connected to the measuring unit in a state, in which the second electrical contact ( 9 ″) and the sample liquid ( 4 ) are spaced apart from each other or rather the second electrical contact ( 9 ″) is not immersed in the sample liquid ( 4 ).

10. Pipetting device according to claim 7 , wherein the second electrical contact ( 9 ″) is connected to ground and separated from the measuring unit in a state, in which the second electrical contact ( 9 ″) and the sample liquid ( 4 ) are in communication with each other or rather the second electrical contact ( 9 ″) is immersed in the sample liquid ( 4 ).

11. Liquid processing system, comprising a pipetting device according to claim 1 , a measuring unit configured to determine a volume of the aspirated or dispensed sample liquid ( 4 ′) depending on the capacitance of the measuring capacitor, and a low-impedance converter circuit, wherein the first electrical contact ( 9 ′), which is configured to establish an electrical connection to the working fluid ( 7 ), and the measuring unit are electrically connected to each other via the low-impedance converter circuit.

12. Liquid processing system according to claim 11 , further comprising a pressure-generating means, wherein the pressure-generating means is connected to a controller configured to, in a closed control loop, based on the volume of aspirated or dispensed sample liquid ( 4 ′) determined by the measuring unit, and a predetermined target volume of the aspirated or dispensed sample liquid ( 4 ′), apply a pressure to the working fluid ( 7 ) for aspirating or dispensing sample liquid ( 4 ′).

13. Liquid processing system according to claim 11 , further comprising a motorized transport unit, in particular a robot arm, on which the pipetting device is arranged, wherein the controller additionally sends signals to the transport unit in order to move the pipetting device such that the opening ( 3 ) of the tube ( 1 ) is precisely positionable, in particular in a sample container ( 10 ) filled with the sample liquid ( 4 ), in particular a sample tube or a microplate.

14. Liquid processing system according to claim 11 , further comprising a third switching element (S 9 ″) which electrically connects or disconnects the second electrical contact ( 9 ″) to or from the measuring unit.

15. Liquid processing system according to claim 11 , further comprising a third switching element (S 9 ″) which electrically connects or insulates the second electrical contact ( 9 ″) to or from ground.

16. Liquid processing system according to claim 15 , wherein the third switching element (S 9 ″) insulates the second electrical contact ( 9 ″) from ground in a state, in which the second electrical contact ( 9 ″) and the sample liquid ( 4 ) are spaced apart from each other or the second electrical contact ( 9 ″) is not immersed in the sample liquid ( 4 ).

17. Liquid processing system according to claim 15 , wherein the third switching element (S 9 ″) connects the second electrical contact ( 9 ″) to ground in a state, in which the second electrical contact ( 9 ″) and the sample liquid ( 4 ) are in communication with each other or the second electrical contact ( 9 ″) is immersed in the sample liquid ( 4 ).

18. Method for operating a liquid processing system according to claim 11 in an open control loop, comprising the steps of:

detecting a state, in which the second electrical contact ( 9 ″) of the pipetting device contacts the sample liquid ( 4 );

switching the liquid processing system to volume measurement;

aspirating the sample liquid ( 4 ) by means of the pressure-generating medium; and

determining a volume of the aspirated sample liquid ( 4 ′) as a function of the capacitance of the measuring capacitor.

19. Method for operating a liquid processing system according to claim 11 in a closed control loop, comprising the steps of:

detecting a state, in which the second electrical contact ( 9 ″) of the pipetting device contacts the sample liquid ( 4 );

switching of the liquid processing system to volume measurement; and

aspirating the sample liquid ( 4 ) by means of the pressure-generating medium based on a predetermined volume signal.