EP2412439A1 - Pipette device with throttle position in the pipette channel - Google Patents

Abstract

The device (10) has a pipette duct (12) whose throttle point (42) is arranged fluid-mechanically between a metering liquid receptacle (38) and a pressure change device (40). The point is being dimensioned in such a way that ratio of flow resistance (R1) of a pipette opening (36) for dispensed metering liquid to flow resistance (R2) of the throttle point for working fluid is less than 0.5. Flow resistances of respective tapering of cross-section of flow are being calculated under consideration of product of viscosity of the working fluid and the metering liquid.

Description

The present invention relates to a pipetting device for at least dispensing dosing liquid by increasing the pressure of a working fluid, comprising a dosing liquid receiving space at least partially filled with working fluid having a pipetting opening as a first flow cross-sectional constriction through which dosing liquid is withdrawn from the dosing liquid as a function of the pressure of the working fluid. Receiving space is dispensed out, and a pressure changing device, which is adapted to change the pressure of the working fluid in the dosing liquid receiving space.

Such pipetting devices are well known in the art. In the dispensing of dosing liquid, a dosing liquid present in a dosing liquid receiving space is expelled by increasing a pressure of a working fluid, which is likewise located in the dosing liquid receiving space, through a pipetting opening of the dosing liquid receiving space in a manner known per se.

Since the pipetting opening generally represents a narrowest flow cross-section when expelling the metering liquid from the metering liquid receiving space, the pipetting opening forms a first flow cross-sectional constriction of the pipetting device discussed here.

Pipetting devices of the type mentioned are used, for example, as washing heads, in which the dosing liquid receiving space filled by a dosing liquid inlet or at least partially filled and then expelled by the dispensation described by means of overpressure of the working fluid based on the ambient pressure of the liquid receiving space from the latter.

In these washing heads, the dosing liquid is a washing liquid which is discharged through the pipetting opening to clean an object provided thereunder, such as a container, with the washing liquid. Again, it depends on a correct sizing of the delivered amount of washing liquid.

In principle, however, should not be ruled out that washing heads the dosing liquid, so as washing liquid, additionally or alternatively to the aforementioned inlet by aspiration known per se, ie by means of a negative pressure of the working fluid in the dosing liquid receiving space through the pipetting opening into the dosing liquid receiving space take up.

A problem of the aforementioned pipetting device, in particular in its design as a washing head, is that form deposits by the repeated expelling of dosing through the pipetting at this or on a channel which leads to the pipetting, which the flow cross section of the pipetting or change the channel leading to the pipetting opening. This results in changes in the metering, so that after some operating time substantially identical pipetting, which are operated with the same metering liquid and otherwise the same operating parameters, can show undesirable different dosing behavior.

It is therefore an object of the present invention to develop a pipetting device of the type mentioned in such a way that its dosing is made less sensitive to changes in the flow cross-section of the pipetting or the pipetting opening channel of the dosing liquid receiving space, so that possible or even probable deposits on the Pipetting orifice do not affect the dosing of the Pipettiervorrichtung or at least less than previously.

This object is achieved according to the present invention by a generic pipetting device, in which the pipetting device in a fluidly filled with working fluid pipetting channel fluid mechanically between the Dosierflüssigkeits receiving space and the pressure changing device has a throttle point as a further flow cross-section constriction, which is dimensioned such that a ratio of a flow resistance (R ₁ ) of the pipetting opening for dispensed dosing liquid to a flow resistance (R ₂ ) of the throttle point for working fluid, which flows through the throttle point in the dispensing of the dosing, less than 0.5, preferably less than 0.3, more preferably less than 0.225 , wherein the flow resistances of the respective flow cross-sectional constriction are calculated taking into account the product of the viscosity of the Me associated with the respective flow cross-sectional constriction dium of working fluid and dosing liquid and the characteristic length of the associated flow cross-section constriction, divided by the fourth power of the characteristic dimension of the flow cross-section of the associated flow cross-sectional constriction.

With the described throttle point, a constriction in the flow cross section is created between the pressure changing device and the metering liquid receiving space, which ensures that caused by the pressure changing device pressure change in the working fluid does not abruptly, but only gradually in the Dosierflüssigkeits receiving space, which surprisingly for a Insensitivity of the dispensing behavior of the pipetting device to changes, in particular deposition-related changes, of the flow cross-section of the pipetting opening provides. Thus, substantially identical pipetting devices, which are operated essentially with identical settings, can have a substantially identical dispensing behavior, even though deposits of different thickness are present at their pipetting orifices.

The ratio of said flow resistances, which is decisive for the functioning of the solution presented here, leads to the throttle point through which the working fluid, as a rule a gas, has a significantly smaller cross-sectional opening than the pipetting opening. However, it should not be excluded that a liquid is used as a working fluid.

The viscosity used here is the respective dynamic viscosity, which is usually denoted by the formula symbol "η" in the literature.

The designated characteristic length of the associated cross-sectional constriction may be the length of the cylindrical channel in the case of cylindrical flow cross-sectional constrictions, or may be the length of the channel section in which the flow cross-sectional area of the channel starts from the smallest flow cross-sectional area in the throttling point or in the case of channels tapering to the flow cross-sectional constriction Pipetting opening doubled. If no doubling of the flow cross-sectional area takes place over the maximum detectable length of the channel, then the entire length of the channel can be used as a characteristic length.

As a characteristic dimension of the flow cross-section can be used for circular flow cross-sections diameter, square flow cross-sections edge length, rectangular flow cross sections arithmetic mean of long and short edge length, elliptical flow cross-sections arithmetic mean of long and short axis, etc. If the flow cross-section changes over the length of the flow cross-sectional constriction, the smallest flow cross-section occurring in the flow cross-sectional constriction should be used.

The use of characteristic dimensions is well known in fluid mechanics.

wobei η_Pof die dynamische Viskosität einer die Pipettieröffnung durchströmenden Dosierflüssigkeit, η_Dst eine dynamische Viskosität eines die Drosselstelle durchströmenden Arbeitsfluids, l_Pof eine charakteristische Länge der Pipettieröffnung, l_Dst eine charakteristische Länge der Drosselstelle, d_Pof eine charakteristische Abmessung des Strömungsquerschnitts der Pipettieröffnung und d_Dst eine charakteristische Abmessung des Strömungsquerschnitts der Drosselstelle ist.Preferably, the ratio of the flow resistance (R ₁ ) of the pipetting port and the flow resistance (R ₂ ) of the throttle point is calculated from: $$\frac{R_1}{R_2}=\frac{{\eta }_{\mathit{pof}}\cdot l_{\mathit{pof}}\cdot d_{\mathit{Dst}}^4}{{\eta }_{\mathit{Dst}}\cdot l_{\mathit{Dst}}\cdot d_{\mathit{pof}}^4}$$

where η _{Pof is} the dynamic viscosity of a dosing liquid flowing through the pipetting opening, η _{Dst is} a dynamic viscosity of a working fluid flowing through the throttle body, l _{Pof is} a characteristic length of the pipetting _opening , l _{Dst is} a characteristic length of the _orifice , d _{Pof is} a characteristic dimension of the flow cross section of the pipetting _opening and d _{Dst is} a characteristic dimension of the flow area of the orifice.

The present invention preferably relates to a wash head pipetting device already mentioned above, which is designed to dispense washing liquid as dosing liquid in precise dosages. Such washing head pipetting devices generally serve to clean objects received in sample containers, such as "wells", by dispensing a precisely metered quantity of washing liquid. In this case, the exact dosage of the washing liquid is of great importance for bringing about a predetermined state of cleaning. In general, the volume flow of washing liquid is adjusted so that the washing performance is as large as possible, but the duration of the washing process is as short as possible. If the washing liquid is incorrectly pipetted, there may be the danger of a so-called "over-washing", which may lead to undesirable elements being loosened on the object to be washed or / and in the sample container.

Although it should not be ruled out that such a washing head pipetting device aspirates the washing liquid as Dosierflüsigkeit over the pipetting into the dosing liquid receiving space, for reasons of simpler handling the dosing liquid receiving space of a preferred washing head pipetting washing liquid supplied as dosing liquid through a dosing liquid feed.

Therefore, therefore, the washing head pipetting device discussed here can have a dosing liquid inlet, through which the dosing liquid receiving space with dosing liquid, ie in the present application with washing liquid, at least partially fillable. For this purpose, it can be provided that the metering liquid feed opens into the metering liquid receiving space. The metering liquid inlet is usually - apart from the advantageous mouth just described - designed as a separate trained by metering liquid receiving channel.

For operation of the dosing liquid feed, the washing head pipetting device may comprise a dosing liquid pump in a further advantageous embodiment of the present invention, with which dosing liquid, in particular scrubbing liquid as dosing liquid, can be conveyed along the dosing liquid feed into the dosing liquid receiving space. Furthermore, in order to prevent unwanted trailing of metering liquid from the metering liquid inlet into the metering liquid receiving chamber, a valve may be provided on the metering liquid inlet, in particular in an area close to the mouth, which can be opened and closed by a control device. Incidentally, the metering liquid pump can also be operated with this or another control device.

However, the dosing liquid pump mentioned above does not have to be provided, since the dosing liquid, in particular as scrubbing liquid, passes from a geodetic over the mouth of the dosing liquid feed into the dosing liquid receiving space Gravity-driven can be promoted. Then, however, the above-mentioned valve is absolutely necessary.

In order to increase the washing efficiency of a washing head pipetting device, it may have a plurality of pipetting channels provided substantially parallel to each other such that a plurality of objects corresponding to the plurality of pipetting channels may be simultaneously subjected to cleaning by the washing head pipetting devices.

Especially with a multichannel pipetting device, the present invention is of great advantage, since the invention can ensure that each pipetting channel can deliver substantially the same amount of dosing liquid with high accuracy, even though the individual pipetting channels, be it pipetting tips coupled by manufacturing tolerances, are it may have different geometric Frmen by different strong deposits on the pipetting, it may be a combination of these or other causes, so that would provide different pipetting results for the same operating parameters of the pipetting without the application of the present invention, the individual pipetting a multi-channel pipetting.

The principle of throttling the working fluid flow between dosing liquid receiving space and pressure varying device can be successfully applied not only to the dispensing of dosing liquids but also to their aspiration. Again, it may lead to insensitivity of the dosing behavior against deposits and other flow cross-section changes in the pipetting.

Therefore, the present invention also relates in particular to pipetting devices which, in addition to the above-mentioned dispensation, also for the aspiration of dosing liquid, in this case by reducing the size of the dosing liquid Pressure of the working fluid in the dosing liquid receiving space, are formed. In this case, when aspirating dosing liquid, it can be aspirated into the dosing liquid receiving space as a function of the pressure of the working fluid through the pipetting opening.

In the case of dosing operations, ie the aspiration and the dispensing of dosing liquid, in the pipetting devices in the prior art with identical pipetting devices and substantially identical operating parameters differences in dosing for different dosing liquids, especially for different viscous dosing detected.

It has been found that the presently recommended throttle point in the pipetting fluid-mechanically between the pressure-changing device and the metering liquid receiving space is also suitable within certain limits to equalize the metering across different viscous metering liquids away. In other words, with essentially identical pipetting devices and essentially the same operating parameters, the metering behavior of these pipetting devices is, within certain limits, independent of the viscosity of the metering liquid.

However, this requires, compared to the previous case of a substantially independent of changes in the Pipettieröffnungs flow cross-section metering, a significant reduction of the flow cross-section of the throttle point.

Experiments have shown that the dosing behavior of essentially the same pipetting devices is essentially independent of the viscosity of the dosing liquid at essentially the same operating parameters, when the ratio of the flow resistance (R ₁ ) of the dispensed dosing liquid pipetting opening to the flow resistance (R ₂ ) of the throttling point for this during the dispensation of the dosing fluid flowing through Working fluid is less than 0.001, preferably less than 0.00075, more preferably less than 0.0005.

Again, the independence of dosing behavior from viscosity applies to both the dispensing and aspiration behaviors. Only the dispensation is used as reference.

Experiments have shown that the above-mentioned upper limits of the ratio of the flow resistances then cause a metering behavior which is substantially independent of the viscosity of the metering liquid, if the dynamic viscosity of the metering liquid is 0.004 Nsm ^-2 , preferably 0.0035 Nsm ^-2 preferably does not exceed 0.0031 Nsm ^-2 .

In this case, working fluids can be used successfully whose dynamic viscosity does not exceed the value of 0.00003 Nsm ^-2 , preferably of 0.00002 Nsm ^-2 , more preferably of 0.0000175 Nsm ^-2 . Again, the dynamic viscosity is meant.

Further, it may be thought to equip the throttle body with an optionally variable flow cross-section, such as by changing the gap width of an annular gap or with a mechanism similar to that used to adjust the aperture on mechanical cameras. Thus, the flow cross section of the throttle point can be adapted to the particular working fluid used and / or each metered dosing liquid.

For better controllability, in particular finely controllability of an aspiration and / or dispensing operation, it can further be envisaged that the pipetting channel is adjustable between a blocking position in which a working fluid flow in the pipetting channel is prevented and an open position in which a working fluid flow in the pipetting channel is permitted Valve has. The valve can initially be closed until the working fluid has been brought to a desired pressure in an area located at least near the pressure changing device. In particular, the throttle point can be variable up to a cross section of zero, so that the valve described here can be realized by using an advantageously small number of components through the above-described throttle point with variable flow cross-section.

Furthermore, a quantity of liquid can be metered with high precision in a manner known per se by intermittently opening and closing the valve.

As described above, since the effect of the presently discussed invention resides in the fact that a pressure change originating from the pressure changing device can not suddenly propagate into the dosing liquid receiving space, it is advantageous, albeit the valve at the throttle or fluid mechanically, between the pressure changing device and the throttle is provided.

According to a structurally possible embodiment of the present invention, at least one reservoir of working fluid under a system pressure can be provided as the pressure changing device. More specifically, to perform both aspiration and dispensing operations on one and the same pipetting channel, provision is made for a dispensing reservoir under a first system pressure and an aspiration reservoir under a second system pressure, which can optionally be connected to the pipetting channel in a pressure-transmitting manner and separable therefrom, wherein the first system pressure is greater than an ambient pressure of the pipetting device and the second system pressure is less than the ambient pressure.

With regard to the flow processes of the working fluid through the throttle point, it is advantageous in aspiration and dispensing processes when the system pressure, at least for dispensing operations the ambient pressure of the metering liquid receiving space does not exceed an overpressure of 1.5 bar, preferably 1.2 bar, particularly preferably 1.0 bar. At higher pressure differentials between the system pressure and the ambient pressure, highly turbulent flows of the working fluid through the orifice may occur, which may affect the effect of the present invention.

In principle, however, it can also be thought that the pressure changing device has a discontinuously or continuously operating pump, optionally in conjunction with a valve arrangement which can be arranged in the conveying path of the pump and optionally opened and closed. With regard to an always desired automation of dosing operations, it is advantageous if the pump is driven by a motor.

Likewise, according to a further advantageous embodiment of the pipetting device, it can be thought that the pressure changing device has a piston-cylinder device with a cylinder extending along a cylinder axis and with a piston movably received therein along the cylinder axis, with the cylinder and piston defining at least one working volume which is variable by a relative movement of the piston relative to the cylinder and which is in fluid communication with the pipetting or can be brought. The piston-cylinder arrangement represents the most common embodiment of the pressure changing device in pipetting devices. It also offers the possibility of a very accurate pressure control through the use of small piston surfaces and in relation to long piston strokes.

Especially with the aforementioned piston-cylinder device as the pressure-varying device, the pipetting device can also be a manually operated pipetting device, in which case in particular the piston can be moved by manual actuation relative to the cylinder. This operation can be immediate, so by pulling out or pushing the piston by hand, or may indirectly, for example by tensioning a spring, which drives a relative movement between the piston and cylinder after triggering, take place. The manually operable pipetting device preferably has only one pipetting channel for metering as precisely as possible.

With "intended operation manually" such cases should not be detected, which are basically operated by motor or otherwise automated and can be operated only for the failure of a power supply by a manual emergency operation.

Especially for cases of dosing by aspiration and dispensation, it is advantageous to meet the highest hygiene standards, when the dosing liquid receiving space and the pipetting formed separately on one of the throttle body having pipetting channel, optionally connectable with this and / or separable from this pipetting tip are. By contrast, outlets, so-called "wash tubes", which are rigidly provided with the pipetting device, are preferred for the aforementioned washing head pipetting device.

The present invention will be explained in more detail below with reference to the attached drawing, which shows a rough-schematic longitudinal section through an embodiment according to the invention of a pipetting device.

In FIG. 1 is a roughly schematically illustrated embodiment of a pipetting device according to the invention generally designated 10. The pipetting device 10 comprises a pipetting channel 12, to which a pipette tip 14 is detachably coupled in a manner known per se.

The pipetting channel 12 has a cylinder portion 16, in which a piston 18 along a coincident with the cylinder axis Z longitudinal axis L of the pipetting device 10 via a piston rod 20 by a motor 22 relative to the cylinder portion 16 is adjustable.

The motor 22 is controlled by a control / regulating unit 24, for example, in response to the detection signal of a pressure sensor 26, which detects the pressure of a working fluid, such as air, in a variable by the movement of the piston 18 working chamber 28.

The pipette tip 14, which is detachable from the pipetting channel 12 in a manner known per se by an ejector 30 which is movable along the longitudinal axis L of the pipetting device 10, has a coupling region 32 for coupling to the pipetting channel 12, one in which FIG. 1 shown conically extending wall portion 34 and a pipetting opening 36 through which a dosing liquid in response to the pressure of a working fluid with which a wall portion 34 and optionally also of the coupling region 32 surrounded dosing liquid receiving space 38 is at least partially filled in the dosing -Absorption space is aspiratable and dispensable from this.

The cylinder 16 and piston assembly 18 form a pressure varying device 40 for varying the pressure of working fluid in the dosing liquid receiving space 38.

wobei η_Dst die dynamische Viskosität des Arbeitsfluids ist, l_Dst eine charakteristische Länge der Drosselstelle 42 in Strömungsrichtung des Arbeitsfluids bei der Dispensation von Dosierflüssigkeit ist und wobei d_Dst eine charakteristische Abmessung des Strömungsquerschnitts der Drosselstelle 42 ist, in dem in Figur 1 gezeigten Beispiel der Durchmesser der Drosselstelle 42 ist. In dem in Figur 1 gezeigten Beispiel ist die Drosselstelle 42 im Wesentlichen durch einen zylindrischen Kanal gebildet, so dass die Länge des Kanals die charakteristische Länge l_Dst der Drosselstelle 42 ist.According to the invention, a throttle point 42 is provided between the pressure changing device 40 and the metering liquid receiving space 38, which has a flow resistance R ₂ for working fluid, which is preferably calculated $$R_2=\frac{128\cdot {\eta }_{\mathit{Dst}}\cdot l_{\mathit{Dst}}}{\mathrm{\pi }\cdot d_{\mathit{Dst}}^4}$$

where η _{Dst is} the dynamic viscosity of the working fluid, _{Dst is} a characteristic length of the throttling point 42 in the direction of flow of the working fluid in the dispensing of dosing liquid, and where d _{Dst is} a characteristic dimension of the flow area of the orifice 42 in which FIG. 1 shown example, the diameter of the throttle body 42 is. In the in FIG. 1 In the example shown, the throttling point 42 is essentially formed by a cylindrical channel, so that the length of the channel is the characteristic length l _{Dst of} the throttling point 42.

The throttle body 42 may further include a valve 44 with which the throttle body 42 is completely lockable to interrupt a pressure propagation of the working fluid pressure from the working space 28 into the dosing liquid receiving space 38.

The valve 44 is preferably also operable by the controller 24.

wobei η_Pof die dynamische Viskosität des die Pipettieröffnung 36 durchströmenden Mediums, also der Dosierflüssigkeit, ist, l_Pof eine charakteristische Länge eines zur Pipettieröffnung 36 führenden Auslassendes der Pipettierspitze 14 ist, und d_Pof eine charakteristische Abmessung des Strömungsquerschnitts der Pipettieröffnung 36, im vorliegenden Regelfall einer kreisförmigen Pipettieröffnung der Durchmesser der Pipettieröffnung 36 ist.On the other hand, the pipetting opening 36 has a flow resistance R ₁ during dispensing, which preferably results $$R_1=\frac{128\cdot {\eta }_{\mathit{pof}}\cdot l_{\mathit{pof}}}{\mathrm{\pi }\cdot d_{\mathit{pof}}^4}$$

where η _{Pof is} the dynamic viscosity of the medium flowing through the pipetting _opening 36, ie the dosing liquid, l _{Pof is} a characteristic length of an outlet end of the pipetting _tip 14 leading to the pipetting _opening 36, and d _{Pof is} a characteristic dimension of the flow cross section of the pipetting _opening 36, in the present case a circular pipetting opening is the diameter of the pipetting opening 36.

At the in FIG. 1 As shown in the example of a pipetting tip 14 tapering conically or otherwise towards the pipetting opening 36, the following convention can be used to determine the characteristic length:

The characteristic length l is the length which has the exit end of the pipette tip 14 from the pipetting opening 36 to the point at which the flow cross-section of the pipette tip 14 has twice the surface area as the pipetting opening 36. Since the circular cross-section is proportional to the square of the radius or the diameter, the length which conical or otherwise tapering to the respective flow cross-sectional constriction with the narrowest flow cross-section can be taken to be the length which exists between the respective flow cross-sectional constriction and a flow cross-section whose diameter is √2 times the diameter the flow cross-sectional constriction is.

It has been found that, with increasing flow cross-sections in the pipetting tip 14 or in the throttling point 42, those regions with a significantly larger flow cross-section than the narrowest flow cross-section hardly contribute to the flow resistance of the respective outlet opening. In other words, those regions of the pipette tip 14 or the throttling point 42, which have a flow cross-sectional area which is more than twice the flow cross-sectional area of the narrowest cross-section, only contribute in subordinate orders to the respective flow resistance of the respective flow cross-sectional constriction. They can therefore be neglected.

Then, when the ratio of the two flow resistances at the throttle point 42 and the pipetting opening 36, taking into account the media flowing through the respective flow cross-sectional constrictions, based on their dynamic viscosity, a ratio of 0.5, preferably 0.3, particularly preferably 0.225, is the dispensing behavior of the pipette tip 14, which may also be rigidly connected to the pipetting channel 12, largely independent of changes in the flow cross-section, for example by deposits of dried or / and crystallized dosing.

Of course, the dosage changes with increasing narrowing of the pipetting 36 from below a critical degree of tightness despite the provision of the throttle point 42 in the pipetting 12 fluid-mechanically between the pressure changing device 40 and the metering liquid receiving space 38. However, the limit from which influences of such deposits make the pipetting opening 36 or in an area near the pipetting opening 36 noticeable during dispensing, are pushed further in the direction of a reduction in the cross-section of the pipetting opening 36.

The same applies to the aspiration of dosing.

Then, when the ratio of the flow cross sections R ₂ to R _{1 is} less than 0.001, preferably less than 0.00075, and more preferably less than 0.0005, the Aspirations- and dispensing behavior of the pipetting even within certain limits, regardless of the viscosity be used dosing, so that with the same pipetting device 10 and one and the same operating parameters different viscous dosing liquids can be dosed equal. This greatly simplifies the operation of pipetting devices.

Experiments have shown that dosing liquids with a dynamic viscosity of up to 0.004 Nsm ^-2 , preferably of 0.0035 Nsm ^-2 and most preferably of 0.0031 Nsm ^-2 can be metered by a pipetting device according to the invention without changing the operating parameters.

Dosing tasks of pipetting devices can therefore be significantly simplified with the present invention.

The present invention is particularly applicable to dosing tasks, which a pipetting device 10 has to fulfill as a so-called "washing head pipetting device", if this washing liquid is to be dispensed as dosing liquid in precise doses.

These washhead pipetting devices can be used to clean objects 37 in sample containers 39 or sample containers 39 alone, which are typically located below the pipetting orifice 36, by dispensing a metered amount of washing liquid as dosing liquid.

Such a washing-head pipetting device 10 can for this purpose have a metering liquid inlet 50 which, starting from a metering liquid reservoir 52, can open into the metering liquid receiving space 38 at an opening 54.

In this case, the metering liquid receiving space is advantageously filled by the metering liquid feed 50 with metering liquid (then in the form of washing liquid), so that the metering liquid need not be aspirated through the pipetting opening 36 in this case.

The dosing liquid in the dosing liquid reservoir 52 can be conveyed through the dosing liquid feed 50 into the dosing liquid receiving space 38 by a pump 56, which may also be controllable by the control / regulating device 24. In order to be able to adjust the delivery rate conveyed by the metering liquid feed 50 even more precisely, a valve 58 can additionally be provided on the metering liquid feed 50, which valve can be opened and closed by the control / regulating device 24.

Thus, for example, by a suitable program in the control / regulating device first with the valve 58 closed by operation of the pump 56, a predetermined pressure in the metering liquid inlet 50 are established, whereupon the valve 58 is opened for a predetermined time and then closed again.

In order to prevent or minimize the dosing liquid from the dosing liquid feed 50 into the dosing liquid receiving space 38, the valve 58 is preferably arranged close to the orifice 54 at the mouth 54 or in relation to the total length of the dosing liquid feed. The distance of the valve 58 from the orifice 54 should preferably not exceed 5% of the total length of the dosing liquid feed 58.

The pipetting device 50, in particular as a washing head pipetting device 10, can have, in addition to the pipetting channel 12 shown, further pipetting channels, which are configured substantially identically to the illustrated pipetting channel 12, so that the in Fig. 1 illustrated pipetting channel 12 is described by way of example for all pipetting channels of a multi-channel pipetting device. For example, washhead pipetting devices may include pipetting channels 12 in a matrix arrangement of 8 x 12 = 96 pipetting channels.

In a multichannel pipetting device, the dosing liquid feeds 50 can then be connected to each pipetting channel 12 via a common pump 56 with a common dosing liquid supply 52.

Likewise, all piston rods 20 of the individual pipetting channels 12 can be adjusted by a common motor 22.

However, it should not be ruled out that each pipetting channel has its own motor 22, its own pump 56 and / or its own dosing liquid reservoir 52.

The aim of the fixing means 60 is to indicate that the pipetting tip 34 can be permanently and simply non-detachably coupled to the pipetting channel 12 as a washing tube. The wash tube can also be formed in one piece with a tube of the pipetting channel, for example with the cylinder section 16.

Claims (15)

Pipetting device (10) at least for the dispensing of dosing liquid by increasing the pressure of a working fluid, comprising: a dosing liquid receiving space (38) at least partially filled with working fluid having a pipetting opening (36) as a first flow area restriction through which dosing liquid can be dispensed in dependence on the pressure of the working fluid from the dosing liquid receiving space (38); - A pressure changing device (40) which is adapted to change the pressure of the working fluid in the dosing liquid receiving space (38),
characterized in that the pipetting device (10) in a fluidly filled with working fluid pipetting channel (12) between the Dosierflüssigkeits receiving space (38) and the pressure changing device (40) has a throttle point (42) as a further flow cross-sectional constriction, which is dimensioned such that a ratio of a flow resistance (R ₁ ) of the dispensing liquid dispensing pipetting orifice (36) to a flow resistance (R ₂ ) of the working fluid restriction (42) flowing through the restriction (42) when dispensing the dispensing fluid is less than 0.5; is preferably less than 0.3, more preferably less than 0.225, wherein the flow resistance of the respective flow cross-sectional constriction (36 or 42) are calculated taking into account the product of the viscosity of the respective flow cross-sectional constriction (36 or 42) associated with the medium of working fluid and do sierflüssigkeit and the characteristic length (l _Dst , l _Pof ) of the associated flow _{cross-sectional constriction} (36 or 42), divided by the fourth power of the characteristic dimension (d _Dst , d _Pof ) of the flow cross-section of the associated flow _{cross-sectional constriction} (36 or 42). Pipetting device (10) according to claim 1,
characterized in that it is a washing head pipetting device (10) which is designed to dispense washing liquid as dosing liquid and which has a dosing liquid feed (50) which preferably opens into the dosing liquid receiving space (38), so that the dosing liquid Receiving space (38) through the metering liquid inlet (50) at least partially filled with Dossierflüssigkeit. Pipetting device (10) according to claim 1 or 2,
characterized in that it comprises a plurality of substantially parallel Pipettierkanälen (12), of which each pipetting channel (12) is provided with one throttle point (42) as the further flow cross-sectional constriction. Pipetting device (10) according to one of the preceding claims,
characterized in that it is also designed for the aspiration of dosing by reducing the pressure of the working fluid, wherein in the aspiration dosing depending on the pressure of the working fluid through the pipetting (36) in the dosing liquid receiving space (38) is aspirin, wherein the Ratio of the flow resistance (R ₁ ) of the dispensing liquid dispensing pipetting opening (36) to the flow resistance (R ₂ ) of the orifice (42) for this working fluid flowing through the dispensing fluid dispensing of less than 0.001, preferably less than 0.00075 than 0.0005. Pipetting device (10) according to one of the preceding claims,
characterized in that the viscosity of the dosing liquid does not exceed the value of 0.004 Nsm ^-2 , preferably of 0.0035 Nsm ^-2 , more preferably of 0.0031 Nsm ^-2 . Pipetting device (10) according to one of the preceding claims,
characterized in that the viscosity of the working fluid does not exceed the value of 0.00003 Nsm ^-2 , preferably of 0.00002 Nsm ^-2 , more preferably of 0.0000175 Nsm ^-2 . Pipetting device (10) according to one of the preceding claims,
characterized in that the throttle point (42) has an optionally variable flow cross-section. Pipetting device (10) according to one of the preceding claims,
characterized in that the pipetting channel (12) has an adjustable valve (44) between a blocking position, in which a working fluid flow in the pipetting channel (12) is prevented, and an open position, in which a working fluid flow in the pipetting channel (12) is permitted. Pipetting device (10) according to claim 8,
characterized in that the valve (44) is provided at the throttle point (42) or fluid mechanically between the pressure changing device (40) and the throttle point (42). Pipetting device (10) according to one of the preceding claims,
characterized in that it comprises, as the pressure changing device (40), at least one reservoir of working fluid under system pressure. Pipetting device (10) according to claim 10,
characterized in that a standing under a first system pressure dispensing reservoir and a standing under a second system pressure aspiration reservoir are provided, which are selectively connectable pressure-transmitting with the pipetting channel (12) and separable therefrom, wherein the first system pressure is greater than one Ambient pressure of the pipetting device (10) and the second system pressure is less than the ambient pressure. Pipetting device (10) according to claim 10 or 11,
characterized in that the system pressure for dispensing operations relative to the ambient pressure of the metering liquid receiving space (38) does not exceed an overpressure of 1.5 bar, preferably 1.2 bar, particularly preferably 1.0 bar. Pipetting device (10) according to one of the preceding claims,
characterized in that the pressure changing device (40) comprises a pump, in particular a motor-driven pump. Pipetting device (10) according to one of the preceding claims,
characterized in that the pressure variation device (40) comprises a piston-cylinder device (16, 18, 20) having a cylinder (16) extending along a cylinder axis (Z) and having a piston movably received therein along the cylinder axis (Z) ( 18), wherein cylinder (16) and piston (18) define at least one working volume (28) which is variable relative to the cylinder (16) by a relative movement of the piston (18) and which is in fluid communication with the pipetting channel (12) or can be brought. Pipetting device (10) according to one of the preceding claims,
characterized in that the dosing liquid receiving space (38) and the pipetting opening (36) on one of the throttle point (42) having pipetting channel (12) separately formed, optionally with this connectable or separable from this pipetting tip (14) are formed.

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