Device and method for pipetting precisely independent of the liquid type

Abstract

The present invention relates to a pipetting device (10) and a pipetting method for pipetting, i.e., aspirating and / or dispensing, a metering liquid (32) independently of the flow characteristics and / or wetting characteristics of a working gas and a metering liquid (32), wherein the pipetting channel (12) has: a first working region (AB1) with a known base temperature (T∞) in a lower base temperature range; and a second working region (AB2) with a known working temperature (TAB2) in a working temperature range increased relative to the base temperature range.

Description

Field of the Invention

[0001] The present invention relates to a pipetting device for aspirating and / or dispensing a metered liquid by means of a working gas, wherein the pipetting device comprises:

[0002] - a pipetting channel extending along a channel axis,

[0003] - a pipetting piston movable along the channel axis in the pipetting channel,

[0004] - a receiving chamber for receiving the metered liquid, the receiving chamber extending along the channel axis in the pipetting channel from a pipetting opening at one end to a piston face of the pipetting piston facing the pipetting opening on the metering side at the other end, wherein a working gas is received in the pipetting channel in a manner adjacent to the piston face on the metering side, wherein the working gas reference volume is defined by the volume of the working gas in the receiving chamber below the working gas reference pressure,

[0005] - a drive device coupled to the pipetting piston in a force-transmitting manner, the drive device being configured to displace the pipetting piston along the channel axis,

[0006] - a position detection device that detects the position of the pipetting piston along the channel axis and outputs a position detection signal representing the detected position,

[0007] - a pressure detection device that detects the pressure of the working gas in the pipetting channel and outputs a pressure detection signal representing the detected pressure, and

[0008] - a control device,

[0009] wherein the control device is configured to control the drive device as follows, taking into account the change in the working gas reference volume induced by the pressure change caused by the piston movement:

[0010] - the pressure detection signal,

[0011] - the working gas reference pressure, and

[0012] - the defined desired metered liquid volume to be aspirated,

[0013] wherein the control device is further configured to perform the piston movement required to aspirate the desired metered liquid volume in a plurality of successive movement steps.

[0014] Furthermore, the present invention relates to a method for correctly aspirating a metered liquid by means of a pipetting device. Background Art

[0015] The pipetting device and pipetting method of the present application only involve the pipetting process in the so-called "Air-Displacement" method, in which there is a working gas volume sealed between the metering liquid to be pipetted and the piston surface of the pipetting piston facing it, and the working gas volume is numerically at least of the order of magnitude of the volume of the metering liquid to be accommodated in the pipetting channel. Usually, the volume of the working gas sealed between the piston surface on the metering side and the metering liquid is greater than the volume of the metering liquid accommodated in the pipetting channel.

[0016] Here, in the present application, the pipette tip that may be coupled to the pipetting device is regarded as part of the pipetting channel. Usually, the metering liquid is only aspirated into such a pipette tip and dispensed from the pipette tip, more precisely from the reservoir aspirated into the pipette tip. Here, the pipette tip usually continues to be not completely filled with the metering liquid. The volume of the sealed working gas amount is usually between 50 μl and 1000 μl. This applies to the prior art as well as the present invention.

[0017] Here, the accuracy of the pipetting process with respect to the amount of the metered liquid accommodated or output is related to the properties of the metering liquid, such as its viscosity, its density, its wetting behavior with respect to the material of the pipetting channel, and its surface tension. If different liquids with the different properties mentioned above are pipetted by the same pipetting device with the same pipetting parameters, such as the displacement path and displacement speed of the piston, then depending on the direction in which the pipetting process runs, usually different amounts of the dispensed or aspirated metering liquid are caused for these two liquids.

[0018] So far, this situation has been taken into account in pipetting technology by dividing the metering liquid into liquid categories with the same or sufficiently similar pipetting properties. For each such formed liquid category, correction values can then be stored in the data memory of the pipetting device, and the correction values are applied to the pipetting parameters in order to displace the pipetting piston such that the actual volume of the pipetted metering liquid corresponds as precisely as possible to the desired volume to be pipetted. Thus, for example, for a liquid with a particularly high viscosity (which has a high flow resistance), the volume to be passed through by the pipetting piston can be a specific multiple larger than the volume of the metering liquid to be displaced by the movement of the pipetting piston and / or the displacement speed of the pipetting piston can be reduced from the standard value during pipetting in order to compensate for the high flow resistance and pipette the desired amount of metering liquid as precisely as possible.

[0019] Disadvantageously, the liquid category of the liquid to be aspirated must be known in order to be able to aspirate the liquid as precisely as possible by means of the air displacement method. In fact, for a large number of metered liquids, there are multiple liquid categories and category-related correction values. However, significant difficulties arise if a metered liquid of unknown category is to be aspirated, for example a metered liquid produced by mixing different liquids and not associated with any liquid category. Then it is necessary to either associate the unknown metered liquid with a liquid category through time-consuming tests or to create and define a new liquid category in order to be able to aspirate the unknown metered liquid correctly.

[0020] A pipetting device of the type initially mentioned is known from EP 1 250 956 B1. This document discloses a pipetting device in which the pressure change caused by the movement of the pipetting piston in the working gas volume enclosed in the pipetting channel is taken into account in order to be able to determine as precisely as possible the working gas volume enclosed in the pipetting channel after the end of the piston movement for pipetting and to be able to deduce from this as precise a determination the volume of the metered liquid present in the pipetting channel. According to its own explanation, this document is based on the ideal gas equation. However, in practice, the compensation of the volume change induced by the pressure change of the working gas taught in EP 1 250 956 B1 is based on a special case of Boyle-Mariotte's law, since EP 1 250 956 B1 is based on a purely isothermal state change of the working gas.

[0021] Additionally, the pipetting method known from this document takes into account a purely empirical residual amount of metered liquid which, after the end of the piston movement for pipetting (possibly due to inertia), flows back in through the pipetting opening of the pipetting channel. EP 1 250 956 B1 does not mention the exact reason for the residual amount flowing back in and only refers to the empirical facts regarding its determination.

[0022] A pipetting device is known from US 5895838 A, the pipetting channel of which has two differently temperature-controlled zones, namely a zone closer to the pipetting piston with a higher working gas temperature and a zone closer to the pipetting opening with a lower working gas temperature. If the pipetting piston moves, the working gas thus moves from one zone into the other and is heated or cooled depending on the direction of movement, which in turn causes a volume change of the heated or cooled amount of working gas. This document teaches that the volume change induced by the temperature of the working gas is used to correct the desired volume to be aspirated and the correspondingly increased or decreased desired volume is aspirated.

[0023] The temperature compensation of the desired pipetting volume taught in US 5895838 A is carried out according to Gay-Lussac's law, which presupposes an isobaric state change, i.e., a constant pressure of the working gas that is heated or cooled.

[0024] From DE 196 51252 A1, methods and devices for non-contact determination of the volume of a material accommodated in a closed container are also known. For this purpose, exactly one state variable of the gas fraction contained in the closed container, i.e., pressure, volume, temperature, or quantity, is numerically changed, and the gas volume and ultimately the material volume are inferred from the resulting changes in the remaining state variables of the gas fraction using the ideal gas equation. Summary of the Invention

[0025] Based on the above, it is an object of the present invention to provide the following technical teaching, which enables precise pipetting of a liquid without prior determination of its liquid type and without prior determination of its pipetting-related physical properties such as viscosity, density, wettability, surface tension, etc.

[0026] According to a first aspect of the present invention, the object is achieved by a pipetting device of the type initially mentioned, the pipetting channel of which has: a first working area, the known basic temperature of which is in a lower basic temperature range; and a second working area, the known working temperature of which is in a working temperature range increased relative to the basic temperature range, wherein the control device is configured to, after a first pipetting piston movement step, for subsequent pipetting piston movement steps,

[0027] - Determine a first correction variable based on the position detection signal, the pressure detection signal, and the working gas reference pressure, the first correction variable representing the volume change induced by the pressure change of the part of the working gas volume enclosed in the pipetting channel that is in the first working area, and

[0028] - Determine a second correction variable based on the position detection signal, the pressure detection signal, the working gas reference pressure, the known working temperature, and the known basic temperature, the second correction variable representing the volume change induced by the pressure change and the temperature change of the part of the working gas volume enclosed in the pipetting channel that is in the second working area,

[0029] And based on or taking into account

[0030] - A step reference volume associated with the subsequent pipetting piston movement step,

[0031] - The volume displaced so far of the piston face on the metering side of the pipetting piston during the current pipetting process,

[0032] - The first correction variable, and

[0033] - The second correction variable,

[0034] to determine the desired stepped movement volume of the pipetting piston and to control the drive device based on the determined desired stepped movement volume.

[0035] Preferably, the working gas reference pressure is the pressure of the working gas at the start of the pipetting process. If the pipetting channel is filled only with the working gas before the aspiration process, then the working gas reference pressure is preferably the ambient pressure of the pipetting device, since the working gas in the pipetting channel is then in pressure compensation connection with the gas of the surrounding atmosphere via the pipetting opening. If a certain amount of metering liquid is already present in the pipetting channel at the start of the aspiration process, then the working gas reference pressure can again be the ambient pressure or the working gas pressure at the start of the aspiration process. This also applies to the dispensing process. At the start of the dispensing process, there is always a certain amount of metering liquid present in the pipetting channel, which is dispensed via the pipetting opening. Here, the working gas reference pressure can also be the working gas pressure at the start of the dispensing process, or can be the ambient pressure.

[0036] In the present application, the "pipetting process" or "current pipetting process" refers to the pipetting process associated with the accommodation or output of the desired metering liquid volume as a result of pipetting.

[0037] The working gas reference volume can be the dead volume present between the pipetting opening and the piston face on the metering side of the pipetting channel that is filled only with the working gas in a predetermined position of the pipetting piston in the pipetting channel. For example, in the reference state where the pipetting piston is at its bottom dead center, the pipetting channel is filled only with the working gas and the pipetting opening is idle, such that it is possible to connect the pressure of the working gas to the external environment of the pipetting device. By immersing the pipetting opening into the metering liquid reservoir, the dead volume can be physically separated from the external environment. When the pipetting opening is placed at the liquid level of the metering liquid reservoir, the ambient pressure prevails in the working gas that is then separated from the external environment in the pipetting channel.

[0038] The desired metering liquid volume is usually preset as the desired value of the pipetting process and is thus known.

[0039] The stepped reference volume for the movement steps of the pipetting piston can be preset, i.e., pre-determined, independently of the desired metering liquid volume to be pipetted, for example, taking into account the structure and kinematics of the pipetting device.

[0040] Alternatively, the control device can determine a step reference volume for subsequent pipetting piston movement steps as a basic measure for the movement to be traversed by the piston face on the metering side based on the desired metered liquid volume. This can be achieved, for example, by using a calculation equation stored in a data memory, which calculates the step reference volume for one or more pipetting piston movement steps based on a predetermined number of pipetting piston movement steps for performing a pipetting process for pipetting the desired metered liquid volume and, in addition, based on the desired metered liquid volume to be pipetted during the pipetting process. Alternatively, this can be achieved by reading the step reference volume from a preset data relationship that associates the step reference volume with the individual pipetting piston movement steps based on the number of pipetting piston movement steps and the desired metered liquid volume as output data.

[0041] The step reference volume can be a series of values preset fixedly for a predetermined number of pipetting piston movement steps. Alternatively, the step reference volume can, for example, be the quotient formed by the desired metered liquid volume and the predetermined number of pipetting piston movement steps. If the desired metered liquid volume is to be divided evenly among all pipetting piston movement steps, the predetermined number of pipetting piston movement steps can be the total number of pipetting piston movement steps of the pipetting process.

[0042] Preferably, the desired metered liquid volume is divided among pipetting piston movement steps, the number of which is less than the total number of pipetting piston movement steps of the pipetting process, such that the pipetting process additionally includes pipetting piston movement steps in which the piston moves with a relatively small movement volume compared to the pipetting piston movement steps of the desired metered liquid volume, mainly or only for correcting the metered liquid volume already accommodated in the pipetting channel, but not for accommodating a larger metered liquid quantity. However, the step reference volume preferably differs numerically for the individual pipetting piston movement steps of the pipetting process in order to be able to take into account the knowledge and experience gained so far regarding the pipetting of liquids. Thus, for example, during pipetting, especially aspiration, the incremental step reference volume for pipetting piston movement steps closer to the start of the pipetting process is preferably numerically greater than the incremental step reference volume for pipetting piston movement steps closer to the end of the pipetting process. Thus, the spillage and / or reflow behavior of the metered liquid during pipetting, especially aspiration, can be taken into account.

[0043] A predefined or determinable step reference volume as described above serves as the basic movement step of the pipetting piston along the channel line for the pipetting piston movement steps to follow respectively. The step reference volume oriented towards the desired metering liquid volume and the desired step movement volume associated with the same pipetting piston movement step do not differ numerically as much as the predefined step reference volume and the associated desired step movement volume of the same pipetting piston movement step that are independent of the desired metering liquid volume. However, this is not important for pipetting success, because which share of the desired step movement volume sought for the pipetting piston movement step is based on the step reference volume and which share is based on the step correction movement volume that supplements the step reference volume to the desired step movement volume is basically unimportant.

[0044] Since the currently discussed open-loop or closed-loop control of the pipetting process that is independent of the liquid type does not focus on metering the liquid due to the working gas interacting with the pipetting piston in the pipetting channel, but focuses on the working gas, and thus preferably based on the ideal gas equation that can very well predict the performance of the working gas, the movement range of the pipetting piston is represented as a volume in this application. The volume can be directly processed by means of the ideal gas equation. According to the known dimensions of the piston face on the metering side through corresponding designs, the step volume can be easily converted into the pipetting piston step along the channel line, and the pipetting piston can be controlled to perform the corresponding movement.

[0045] The control device can be an electronic data processing device, for example including at least one integrated circuit. Preferably, the control device has a data memory in which a running program and running data are stored, and based on the running program and running data, the electronic data processing device outputs control instructions to the drive device.

[0046] The working gas can be any working gas. In many application cases, the working gas is simply air. However, for example when the metering liquid to be processed has requirements in this regard, the working gas can also be an inert gas such as helium or argon, or a quasi-inert gas such as nitrogen or carbon dioxide.

[0047] The moved volume of the piston face on the metering side up to the pipetting piston movement step to follow in the current pipetting process is the volume swept by the displacement of the piston face on the metering side along the channel line during the running of the current pipetting process. This displaced volume takes into account the pipetting operations performed so far in the pipetting process. Therefore, the displaced volume is a measure of the pipetting work completed up to the subsequent pipetting piston movement step in the current pipetting process.

[0048] By means of the hitherto movement of the pipetting piston, the amount of working gas present in the pipetting channel is manipulated. The amount of working gas is displaced and / or its volume is changed, i.e., expanded during aspiration and compressed during dispensing, for example. The correction variables mentioned above can be considered: the first correction variable and the second correction variable, in order to determine as precisely as possible the effect of the hitherto pipetting piston movement on the working gas during the pipetting process. Thus, it is then possible to determine as precisely as possible the metering liquid amount present in the pipetting channel due to the modified working gas.

[0049] Therefore, by gradually performing the pipetting piston movement and determining the desired step movement volume for each subsequent pipetting piston movement step taking into account the parameters mentioned above, it is possible to aspirate the desired metering liquid volume to be aspirated by means of the pipetting process with high precision.

[0050] For the sake of simplicity, the pipetting channel is observed by dividing it into two working regions. In principle, it should not be excluded that other working regions are still defined, however two working regions are already sufficient for a highly precise pipetting result. The difference between the working regions lies in the temperature present therein, where the temperature of the working gas is decisive here. For the first working region, in which the share of the working gas is in a lower basic temperature range, the first correction variable only takes into account the volume change induced by the pressure change. For the second working region, in which the share of the working gas is in a higher working temperature range, the second correction variable takes into account not only the volume change caused by the pressure change of the working gas share but also the volume change caused by the temperature change of the working gas part.

[0051] The pressure change, which is the cause of the volume change, is caused by the hitherto movement of the pipetting piston. Since the start of the pipetting process, by means of the movement of the pipetting piston, the pressure of the working gas has changed from the initial working gas pressure, in particular the working gas reference pressure, to the currently present working gas pressure. This pressure change is in turn the cause of the change in the amount of metering liquid in the pipetting channel, because, apart from other physical effects, such as friction, the pressure of the working gas present in the pipetting channel is decisive for maintaining a certain amount of metering liquid in the pipetting channel. Therefore, the difference between the current working gas pressure and the working gas pressure at the start of the pipetting process, in particular the working gas reference pressure, is a measure of the change in the amount of metering liquid accommodated in the pipetting channel. However, with the change in the working gas pressure during the pipetting process, the volume of the amount of working gas sealed in the pipetting channel also changes from the initial working gas volume to the changed working gas volume. If the amount of metering liquid present in the pipetting piston after the previous pipetting piston movement step is to be determined, then this volume change needs to be taken into account for each subsequent pipetting piston movement step.

[0052] The first working area is preferably an area that is subject to relatively uniform external conditions. The first working area is preferably arranged, for example, in ambient air having a constant or substantially constant ambient temperature. Accordingly, the first working area preferably includes a pipetting tip that can be detachably coupled to the rest of the pipetting device, and optionally includes a device-fixed section of the pipetting channel that is exposed relative to the ambient air. Starting from said section, it can be assumed without much error that said section is permanently at the constant temperature level of the ambient air.

[0053] The second working area of the pipetting channel can be a section of the pipetting channel that, in contrast to the first working area, is not directly exposed to the ambient air and / or whose temperature is not decisively affected by the ambient air. For said second working area, not only the volume change caused by the pressure change due to the piston movement of the working gas is corrected, but also the volume change caused by the temperature change between the basic temperature and the working temperature of the working gas is corrected.

[0054] On the one hand, by obtaining correction values and by applying said correction values before each pipetting piston movement step, the correction generated in each movement step is numerically smaller compared to when the correction is obtained once for the entire pipetting process. On the other hand, by correcting the step reference volume to the desired step movement volume before each pipetting piston movement step, highly accurate pipetting of the pipetting volume is obtained.

[0055] Currently, if a position detection device detects the position of the pipetting piston along the channel axis, this includes directly detecting the position of the pipetting piston and indirectly detecting the position of said pipetting piston, as long as the detection result represents the position of the pipetting piston. Because then the following purpose is achieved: the position detection device can output a position detection signal representing the position of the pipetting piston. This correspondingly applies, with the necessary modifications, to detecting the pressure of the working gas in the pipetting channel by means of a pressure detection device. The working gas pressure can also be detected directly or indirectly, as long as the detection result represents the working gas pressure in the pipetting channel.

[0056] The present invention is based on the consideration of the volume of the pipetting channel between the pipetting opening and the piston face on the metering side. The entire volume present between the pipetting opening and the piston face on the metering side is either filled with the working gas or filled with the working gas and the metering liquid. Next, the present invention is illustrated by taking the aspiration process, which is more difficult to regulate with high accuracy compared to the dispensing process, as an example. In addition, the initial state of the dispensing process is usually generated by aspiration, such that the aspiration process can be considered to be at the start of each pipetting process.

[0057] At the start of the aspiration process, when the position of the piston face on the metering side is known (which is equivalent to the known position of the pipetting piston), only working gas is present in the pipetting channel between the pipetting opening and the piston face on the metering side, and its volume is called the working gas dead volume V T . If now the pipetting opening is slightly immersed in an external metering liquid reservoir such that the dead volume V T is separated from the external environment, yet the metering liquid does not enter the pipetting channel in a capillary manner through the pipetting opening, then it makes sense to use the working gas dead volume V T now separated from the environment as the working gas reference volume. At that moment, the pressure of the working gas is the working gas reference pressure, and thus this pressure is the ambient pressure p ∞ . The temperature of the working gas is the ambient temperature T ∞ .

[0058] First, the division of the pipetting channel into two differently temperature-controlled working areas should be ignored in order to explain the basic principle on which the present invention is based hereinafter. In the case of ignoring the evaporation process in the pipetting channel and the leakage process at the pipetting channel, the amount of working gas enclosed between the metering liquid and the piston face on the metering side remains constant for further pipetting processes. In contrast, the volume of the enclosed working gas amount does not remain constant.

[0059] If in the immersed state, the piston face on the metering side moves away from the pipetting opening by a displacement volume V Kolben , then due to the negative pressure thus generated with respect to the initially existing ambient pressure, a volume V liquid of the metering liquid flows from the reservoir through the pipetting opening into the pipetting channel. Knowing the volume V liquid of the metered liquid accommodated is very important for a highly accurate aspiration process. In the case of a working gas temperature T1 different from the initial temperature, there is then a working gas pressure p1 in the pipetting channel different from the working gas reference pressure. That is to say, the initial working gas dead volume V T first increases by V Kolben , and then the inflowing metering liquid volume V liquid decreases. Thus, the working gas volume V1 present in the pipetting channel after the pipetting piston movement is:

[0060] V1 = V T + V Kolben - V liquid Equation 1

[0061] According to the ideal gas equation p·V = m·R·T or it follows from the above initial conditions that:

[0062]

[0063] With the aid of Equation 1 and Equation 2, the volume V is obtained for the unknown variable liquid :

[0064]

[0065] That is to say, when p ∞ and p1 can be detected by a pressure detection device, when T ∞ and T1 can be detected by a temperature detection device or when T ∞ and T1 are known and when V Kolben can be detected by a position detection device, in the case of a known V T it is possible to obtain the amount of metered liquid contained by the movement of the pipetting piston by the volume V Kolben V liquid .

[0066] However, due to the differently temperature-controlled working regions of the pipetting channel, complex situations currently arise. Generally, the first working region is closer to the pipetting opening, while the second working region is closer to the piston face on the metering side. According to a preferred improvement of the present invention, the first working region starts at the pipetting opening and extends from the pipetting opening into the pipetting channel, while the second working region exists along the heat source of the pipetting device. If the piston face on the metering side is in the second working region, then between the pipetting opening and the piston face on the metering side, depending on the structural design of the pipetting device, the first working region and the second working region are preferably adjacent to each other and contiguous. The working gas volume V1 sealed in the pipetting channel then consists of the volume fraction AB1 V1 of the first working region and the volume fraction AB2 V1 of the second working region.

[0067] V1 = AB1 V1 + AB2 V1 Equation 4

[0068] Basically, in the present application, the value associated with the first working region is indicated by "AB1", and the value associated with the second working region is indicated by "AB2".

[0069] If the initial working gas dead volume V T has extended into these two working regions, then Equation 4 can already be applied to the initial working gas dead volume V T (see the subsequent Equation 4'):

[0070] V T = AB1 V T + AB2 V T Equation 4'

[0071] Alternatively, the working gas volume enclosed between the metering liquid and the piston face on the metering side can only be displaced during the pipetting process by means of the pipetting piston movement such that the working gas volume extends into both working areas after the displacement process. If the initial working gas dead volume V T initially extends only in one working area, then this is usually the first working area.

[0072] Preferably, it is simply based on the following assumption: The first working area is constantly at a first temperature level, for example represented by the ambient temperature T ∞ . However, the first temperature level can also be any other temperature T AB1 . However, for the reasons mentioned above, it makes sense to assume the ambient temperature as the constant temperature of the first working area. Therefore, the metering liquid is usually only aspirated into the first working area such that the aspirated metering liquid is not heated as much as possible, or particularly preferably does not experience a temperature change in the pipetting channel.

[0073] If, based on the preferred case that the piston face on the metering side is at its bottom dead center or near the bottom dead center at the start of the aspiration process described above by way of example, such that as large a piston stroke as possible is available for accommodating the metering liquid, then the volume V Kolben swept by the pipetting piston during the aspiration process or during its sub-steps can be in the first working area and / or the second working area. Therefore, more generally applicable is:

[0074] V Kolben = AB1 V Kolben + AB2 V Kolben Equation 5

[0075] AB1 V Kolben can be 0, then the entire piston movement is in the second working area. If AB1 V Kolben is not 0, then initially it must hold that AB2 V T = 0, because the initial working gas dead volume V T is then displaced only within the first working area along the channel line by the piston movement, but there is no movement of the working gas fraction between the first working area and the second working area.

[0076] That is to say, it can be approximately considered that during the piston movement, the working gas expands or compresses isothermally in the first working area. This also applies to the fraction of the volume swept by the piston face on the metering side that is in the first working area AB1 V Kolben .

[0077] As long as the entire working gas volume enclosed between the metered liquid and the piston face on the metering side during the pipetting process is only in the first working region, then the open-loop or closed-loop control of the pipetting process is not a problem, because the change in the working gas is then regarded as an isothermal state change and is processed. If the piston face on the metering side moves or starts to move into the second working region, then the present invention comes into play.

[0078] In contrast, the volume of the working gas corresponding to the volume fraction in the second working region of the piston movement AB2 V Kolben moves between the first working region and the second working region. During aspiration, the movement is from the first working region into the second working region, and during dispensing it is in the opposite direction. In the second working region, the temperature of the working gas is T AB2 , where T AB2 >T ∞ . With the movement of the working gas between the first working region and the second working region, a temperature change of the working gas occurs.

[0079] In an isothermal and isobaric piston movement, the volume swept by the piston face on the metering side in the pipetting channel will correspond to the change in the amount of metered liquid in the pipetting channel, because there is no working gas at this point in the pipetting channel and it must be metered liquid.

[0080] However, the piston movement cannot cause an isobaric state change of the working gas, because only a pressure change in the working gas can do work on the metered liquid and move the metered liquid through the pipetting opening.

[0081] Since the working gas moves between the first working region and the warmer second working region, the state change of the working gas caused by the piston movement cannot be isothermal either.

[0082] Due to the assumptions above, the share of the piston movement in the second working region moves the working gas volume AB2 V Kolben . Thereby, the temperature of the working gas volume AB2 V Kolben changes from T ∞ to T AB2 during aspiration, and from T AB2 to T ∞ during dispensing. Additionally, the working gas volume undergoes a pressure change caused by the piston movement.

[0083] The share of the piston movement in the first working region only causes the working gas volume AB1V Kolben The change in pressure. Here, due to the pressure change and temperature change, the working gas volume V corresponding to the volume swept by the piston face on the metering side in total Kolben changes by the following value:

[0084]

[0085] The first working area from the pipetting opening of the pipetting channel extending up to the pipetting opening has a volume V in the pipetting channel AB1 . Under the following simplified assumption: the volume V of the metering liquid accommodated in the pipetting channel caused by the piston movement liquid initially corresponds to the volume V swept by the piston face on the metering side Kolben , if the piston face on the metering side is in the second working area, then the remaining volume of the system retaining the working gas in the first working area AB1 V sys,rest , for which the following applies:

[0086] AB1 V sys，rest ≡V AB1 -V liquid ≈V AB1 -V Kolben Equation 7

[0087] If the piston face on the metering side is initially, i.e., at the start of the pipetting process, in the second working area, then V T can be larger than V AB1 by the initial volume in the second working area AB2 V init . If V T is less than V AB1 , then the piston face on the metering side must first move with AB1 V Kolben until the boundary between the first working area and the second working area. Therefore, considering Equation 5, the most general formulation of Equation 7 is:

[0088] AB1 V sys，rest ≈V T - AB2 V init + AB1 V Kolben -( AB1 V Kolben + AB2 V Kolben )

[0089] =V T - AB2 V init -AB2 V Kolben Equation 7*

[0090] Although only AB2 V init or AB1 V Kolben can be different from 0. Because AB1 V Kolben is always subtracted from the equation, so AB1 V Kolben is unimportant.

[0091] If, as is preferred, V AB1 ≥ V T is applied and logically V AB2 V init = 0, for example because the first working area extends from the pipetting opening beyond the bottom dead center or another initial position of the piston face on the metering side, then Equation 7* can be abbreviated to:

[0092] AB1 V sys，rest ≈ V T + AB1 V Kolben -( AB1 V Kolben + AB2 V Kolben ) = V T - AB2 V Kolben Equation 7'

[0093] Since the remaining volume of the system exists only in the first working area by definition, the subscript "AB1" is subsequently omitted when indicating the remaining volume of the system. Because the remaining volume V sy s ,rest of the system in the given operating state of the pipetting device thus extends from the meniscus of the metering liquid at or in the pipetting channel towards the working gas to the boundary of the first working area remote from the pipetting opening, the remaining volume of the system also includes the volume AB1 V Kolben that may be in the first working area swept by the piston face on the metering side. According to the assumptions above, the remaining volume V sys,rest of the system undergoes an isothermal state change through the piston movement, whereby the remaining volume V sys,rest changes by the following value ΔV sys,rest :

[0094]

[0095] Equations 7* and 7' directly show that the volume swept by the piston face on the metering side in the first working region has already been taken into account in the remaining volume of the system. Considering the share of the piston movement in the first working region and its change induced only by the pressure change in the remaining volume of the system, and further under the meaningful assumption that there is the same working gas pressure p AB2 = p AB1 in the two working regions, since the two working regions can communicate with each other in a balanced pressure manner, only the share of the piston movement in the second working region is retained according to Equation 6. This leads to the subsequent Equation 9 from Equations 6 and 8:

[0096]

[0097] The volume of the metering liquid accommodated in the pipetting channel differs from the volume of the piston movement that causes the metering liquid to be accommodated in the pipetting channel by the volume changes of Equations 8 and 9. Expressed in a formula, this means:

[0098] V liquid = V Kolben - AB2 ΔV Kolben -ΔV sys，rest Equation 10

[0099] With the aid of Equations 6, 7, and 8, Equation 9 can also be written as:

[0100]

[0101] In other groupings, the following Equation 10" is derived from Equation 10':

[0102]

[0103] The volume V T is a pure structural variable of the pipetting device and is thus known. With knowledge of the temperature T AB2 prevailing in the second working region, the volume V Kolben swept by the piston face on the metering side that can be obtained by the position detection device, and its share in the second working region of said volume AB2 V Kolben the pressure p AB1 of the working gas in the pipetting channel that can be obtained by the pressure detection device, as well as the initial parameters p ∞ , T ∞ in the case of, the volume of the metering liquid accommodated in the pipetting channel can be approximately obtained for each pipetting piston movement step independently of the pipetting characteristics of the metering liquid by one of Equation 10", Equation 10', or Equation 10.

[0104] By definition, the temperature quotient is always positive and greater than 1. The pressure quotient is likewise always positive and generally greater than 1, since the working gas pressure in the interior of the pipetting channel cannot become negative and must in the vast majority of cases be less than the ambient pressure in order to be able to hold the metered liquid accommodated in the pipetting channel in the pipetting channel. Exceptions can occur in the case of a small volume of the metered liquid accommodated in the pipetting channel if the particular metered liquid can be held in the pipetting channel only by capillary forces. Then p AB1 can be greater than the ambient pressure p ∞ .

[0105] In equation 10, the term ΔV sys,rest is an example of a first correction variable for the purposes of the present application, and the term AB2 ΔV Kolben is a second correction variable for the purposes of the present application.

[0106] In equation 10', the term is an example of a first correction variable for the purposes of the present application, and is the term is an example of a second correction variable for the purposes of the present application.

[0107] In equation 10", the term is an example of a first correction variable for the purposes of the present application, and the term is an example of a second correction variable for the purposes of the present application.

[0108] In equations 10, 10' and 10", V Kolben is a measure of the displacement volume to date of the piston face on the metering side during the current pipetting process. All of equations 10, 10' and 10" give the same value for V liquid for the same state of the pipetting device.

[0109] At the end of the pipetting process, V liquid maps the desired metered liquid quantity with high precision. During the aspiration process based on the reference state of the pipetting device defined above, the V liquid at the end of the pipetting process is the quantity of metered liquid aspirated that corresponds with high precision to the desired metered liquid quantity. During a pipetting process starting from the initial quantity Start V liquid of the metered liquid in the pipetting channel, the quantity of metered liquid aspirated that corresponds with high precision to the desired metered liquid quantity at the end of the pipetting process is the difference between the initial and final quantities of the metered liquid present in the pipetting channel, i.e. V liquid – Start V liquidHowever, since this initial state of "pre-filling" of the pipetting channel itself must again be attributed to the aspiration process with a pipetting channel initially filled only with the working gas, the operating state of "pre-filling" can likewise be derived from the representations above of the aspiration process. This correspondingly applies to the dispensing process whose initial state must also be aspirated beforehand.

[0110] As already shown above, in order to achieve a particularly precise pipetting result, the control device can be configured to determine, for subsequent pipetting piston movement steps, an estimated value for the amount of metering liquid present in the receiving chamber based on the displacement volume to date of the piston face on the metering side of the pipetting piston, a first correction variable, and a second correction variable during the current pipetting process. For example, such an estimated value can be determined using at least one of the equations 10, 10', and 10″ derived above. Then, V liquid – Start V liquid is the following estimated value, which enables the volume of the metering liquid pipetted in the pipetting channel to be determined as the volume after each pipetting piston movement step. For Start V liquid = 0, i.e., when aspirating the metering liquid based on the reference state above, V liquid itself is the estimated value.

[0111] The control device can also be configured to compare the estimated value thus determined with a step reference volume for subsequent pipetting piston movement steps and to determine a desired step movement volume based on the comparison result. For example, the desired step movement volume can be determined according to the difference between the estimated value and the step reference volume. Here, compared with a smaller difference, a larger difference preferably causes a larger desired step movement volume.

[0112] The step movement volume is preferably used here as the cumulative step movement volume, which represents the sum of all individual step movement volumes that the pipetting piston has traversed during past movement steps. Here, according to the explanations given above, the cumulative step movement volume at the end of the last movement step of the pipetting process preferably corresponds to the desired metering liquid amount recorded as volume. Therefore, the comparison of the estimated value with the cumulative step movement volume corresponds to the comparison between the desired metering liquid volume represented by the cumulative step movement volume associated with the movement steps performed to date and the actual metering liquid volume actually pipetted represented by the estimated value.

[0113] The difference can be converted by the control device into a stepped correction movement volume by means of proportional and / or differential and / or integral conversion terms. The proportional conversion term determines a proportional stepped correction movement volume value based on the difference by means of a proportionality factor to be determined experimentally or empirically. The differential conversion term determines a differential stepped correction movement volume value based on the difference between the current difference and the previous difference, i.e., based on the change in the difference, by means of a differential weighting factor to be determined experimentally or empirically. The integral conversion term determines an integral stepped correction movement volume value based on the sum of the differences while taking into account the current difference by means of an integral weighting factor to be determined experimentally or empirically.

[0114] Then, the desired stepped movement volume following the pipetting piston movement step can be the stepped reference volume associated with the pipetting piston movement step following the correction of the stepped correction movement volume.

[0115] The control device is preferably configured to perform pipetting piston movement steps following one another until the difference between the determined estimated value and the stepped reference volume is below a predetermined difference threshold, in particular for a predetermined number of directly following pipetting piston movement steps. Then, the desired metered liquid volume is usually pipetted with the pipetting accuracy determined by the difference threshold. The abort criterion causes a highly accurate pipetting result especially under the following additional conditions: the stepped reference volume is a cumulative stepped reference volume and the pipetting process continues until the cumulative stepped reference volume corresponds to the desired metered liquid volume.

[0116] Alternatively, the control device can be configured to perform a predetermined number of pipetting piston movement steps following one another, which is also reliably sufficient to correctly pipette viscous metered liquids with a high surface tension. In the case of low-viscosity metered liquids, this can cause that substantially no significant pipetting piston movement occurs anymore before the predetermined number of pipetting piston movement steps is reached, since the estimated value already essentially corresponds to the desired metered liquid volume very early on.

[0117] To achieve a highly accurate pipetting result, the control device can be configured to perform more than 100, preferably more than 1000, particularly preferably more than 10000 pipetting piston movement steps per second. Due to the limits of the kinetics achievable by means of the pipetting piston, the control device is configured to perform fewer than 100000 pipetting piston movement steps per second.

[0118] As already described in detail above, the control device can read from the data memory and / or calculate based on the desired metered liquid volume the stepped reference volume associated with the subsequent pipetting piston movement steps.

[0119] The stepped reference volume can be an incremental stepped reference volume, which indicates, starting from the current location of the piston face on the metering side, the stepped reference volume for a single subsequent pipetting piston movement step, and the piston face on the metering side should pass through this stepped reference volume in the next movement step. Then, the cumulative value of the stepped reference volume obtained by accumulation from the hitherto incremental stepped reference volume advantageously has a first stepped range in the increasing number of steps, in which the cumulative value increases from an initial value to at least 95%, preferably exactly 100%, of the desired metered liquid volume, and the cumulative value has a second stepped range following the first stepped range, in which the cumulative value does not deviate from the range of 95% to 105% of the desired metered liquid volume, preferably does not deviate from exactly 100% of the desired metered liquid volume.

[0120] Alternatively, the stepped reference volume can be an absolute stepped reference volume (also referred to above as the cumulative stepped reference volume), which indicates the end position of the piston face on the metering side starting from its initial position at the beginning of the pipetting process. The value of the absolute stepped reference volume or the cumulative stepped reference volume again has a first stepped range in the increasing number of steps, in which the value of the absolute stepped reference volume increases from an initial value to at least 95%, preferably exactly 100%, of the desired metered liquid volume, and the value has a second stepped range following the first stepped range, in which, in the second stepped range, the value of the absolute stepped reference volume does not deviate from the range of 95% to 105% of the desired metered liquid volume, preferably does not deviate from exactly 100% of the desired metered liquid volume.

[0121] Advantageously, the share of the second stepped range in the entire pipetting process is greater than 20%, preferably greater than 30%, relative to the number of pipetting piston movement steps, whereby there is a calm phase near the end of the pipetting process, in which the pipetting piston mainly performs corrective movements in order to improve the accuracy of the consistency between the desired metered liquid volume and the actually pipetted metered liquid volume. The pipetting piston movement steps performed in this phase usually have a smaller desired stepped movement volume compared to the first stepped range, which enables an as undisturbed and stable regulation of the pipetting process as possible. Therefore, in the second stepped range, the mutual enhancement of disturbances in the pipetting process and their correction are approximately excluded due to the then small desired stepped movement volume. For the same reason, compared to the first stepped range, the second stepped range preferably has at least the same number of steps or even a greater number of steps and / or preferably continues for at least the same duration or even a longer duration.

[0122] In case of doubt, the start of the pipetting process should coincide with the start of the first advancement range, i.e., it should start at the moment from which the incremental advancement reference volume numerically deviates from 0 initially. In the pipetting device according to the invention and the pipetting method according to the invention, although the movement of the pipetting piston can already be caused since the pipetting opening is immersed in the metering liquid reservoir, although the advancement reference volume continues to have only the value 0, for example in order to counteract the flow of the metering liquid through the pipetting opening caused only by capillary forces. However, this piston movement is only a corrective movement that can continue for an arbitrary long time. In case of doubt, if the pipetting piston starts to move by the incremental advancement reference volume changing from 0 initially to a value different from 0, then the pipetting process starts in terms of the invention. The difference between two directly successive cumulative advancement reference volumes or absolute advancement reference volumes is identical to the incremental advancement reference volume here.

[0123] For a regulation method that is as stable as possible and less affected by external influences, the control device can be configured to define the desired advancement movement volume to be determined by quantifying at least two of the following three parameters:

[0124] - The desired end position of the piston face on the metering side at the end of the subsequent pipetting piston movement step,

[0125] - The desired displacement speed of the piston face during the subsequent pipetting piston movement step, and

[0126] - The duration of the subsequent pipetting piston movement step.

[0127] Thus, not only the position of the end face on the metering side can be preset, but also the displacement speed can be preset. For example, for different values of the desired metering liquid quantity and / or different values of the advancement reference volume, different displacement speeds or movement durations can be stored in the data memory mentioned above of the control device.

[0128] As shown above according to Equation 10, Equation 10' and Equation 10", the control device can be configured to form a second correction variable based on the part of the working gas in the second working region and the product formed by the pressure quotient and the temperature quotient, where the pressure quotient is the quotient formed by the detected working gas pressure and the working gas reference pressure, and where the temperature quotient is the quotient formed by the working temperature and the base temperature.

[0129] Advantageous for a highly precise and rapid movement of the piston face on the metering side is that the drive device includes a linear motor, the rotor of which is the pipetting piston. Then, in order to apply a sufficiently high driving force to the pipetting piston, the working device preferably includes a plurality of energizable coils, which are arranged radially outside the pipetting channel along the drive section. In order to achieve as uniform a driving force as possible acting on the pipetting piston, the coils preferably enclose the pipetting channel closed in the circumferential direction around the channel axis. Since the coils energized at least in time intervals form a heat source, the second working area includes the drive section. Therefore, the volume swept by the piston face on the metering side during its displacement is preferably completely within the second working area. For reasons of as predictable a thermal relationship as possible, the first working area extends along the channel line up to the area of the coil arrangement. Therefore, preferably, the section of the pipetting channel extending from the longitudinal end on the pipetting opening side of the area of the coil arrangement up to the pipetting opening is exposed relative to the external environment of the pipetting device and forms the first working area.

[0130] In principle, during operation of the pipetting device, known operating temperatures can occur in dynamic thermal equilibrium in the second working area. The equilibrium operating temperature can be stored in the data memory mentioned above and used to regulate the pipetting process. However, it is safer and more accurate to sense the temperature in the second working area than to rely on a thermal equilibrium state that always reappears again. Therefore, according to a preferred refinement of the invention, the pipetting device has a temperature sensor for detecting the operating temperature, which outputs an operating temperature signal representing the operating temperature.

[0131] To avoid contamination caused by successively pipetting different metering liquids through the same pipetting channel, the pipetting channel preferably has a channel section fixed to the device, which has a coupling assembly and a pipetting tip detachably coupled to the coupling assembly. The pipetting tip then has a pipetting opening. Then, only the metering liquid is pipetted into the pipetting tip, but not into the channel section fixed to the device.

[0132] In addition to the pressure-induced and temperature-induced changes in the reference volume of the working gas during the pipetting process, inevitable leaks in the area enclosing the working gas can also have a negative impact on the pipetting accuracy. For example, the working gas may flow past the pipetting piston, or it may also flow on the coupling assembly for coupling the pipetting tip. Therefore, the control device is preferably configured to determine a third correction variable, which represents the leak in the pipetting channel, wherein the control device is configured to additionally determine the desired step movement volume of the pipetting piston based on the third correction variable. Then, for example, equation 10 above can be modified to:

[0133] V liquid =VKolben -ΔV Kolben -ΔV sys，rest -ΔV Leckage Equation 11

[0134] Here, the leakage volume ΔV is preferably Leckage Assume that the third correction variable is . The third correction variable is preferably related to the configuration-induced leakage rate K as the leakage parameter. L and the pressure p inside the pipetting channel AB1 and environmental pressure p ∞ The pressure difference between the two and the duration of the pressure difference are related to:

[0135]

[0136] In order to quantify the leakage volume as a third correction variable, the control device can be designed to determine the third correction variable based on the pressure detection signal and a duration, in particular a duration of a pipetting piston movement step.

[0137] The control device can also be designed to also be based on the leakage parameter K L Since the leakage parameter can change over time for a given pipetting device, the control device for numerically updating the leakage parameter can also be designed to determine the leakage parameter when detecting a time change of the initially defined working gas pressure due to a leak, based on a manual control input or via a predetermined automated control.

[0138] For example, the control device can couple a pipette tip with a closed pipetting opening or without a pipetting opening to a channel section fixed to the device at regular, predetermined time intervals, based on manual control input or through predetermined automated control, for example, by moving a pipetting piston to set a predetermined pressure of the working gas in the pipetting channel, and detect a change in the working gas pressure over a predetermined duration. The control device can quantify a leakage parameter based on the change in the working gas pressure over the predetermined duration and based on a pressure difference between the working gas pressure in the pipetting channel and the ambient pressure of the pipetting device.

[0139] The pipetting device can have a pressure sensor for detecting the ambient pressure. Alternatively, the ambient pressure can be input manually via an input device.

[0140] The present invention also achieves the above-mentioned object by a method for accurately metering a metering liquid independently of the flow characteristics and / or wetting characteristics of the metering liquid by means of a pipetting device, in particular by means of a pipetting device as described and improved above, wherein the pipetting channel has: a first working area, the known basic temperature of which is in a lower basic temperature range; and a second working area, the known working temperature of which is in a working temperature range increased relative to the basic temperature range, wherein the method performs a step-by-step displacement of a pipetting piston movably accommodated in the pipetting channel, and wherein after a first movement step of the pipetting piston, for subsequent movement steps of the pipetting piston, the method comprises the following method steps:

[0141] - Detecting the pressure of the working gas,

[0142] - Detecting the position of the pipetting piston,

[0143] - Determining a first correction variable based on the detected pipetting piston position, the detected working gas pressure and a working gas reference pressure, the first correction variable representing a volume change induced by a pressure change of a first part of the volume of the working gas sealed in the pipetting channel in the first working area,

[0144] - Determining a second correction variable based on the detected pipetting piston position, the detected working gas pressure, the working gas reference pressure, the known working temperature and the known basic temperature, the second correction variable representing a volume change induced by a pressure change and a temperature change of a part of the volume of the working gas sealed in the pipetting channel in the second working area,

[0145] - Determining an estimate for the metering liquid present in the receiving chamber based on the detected pipetting piston position, the previous pipetting piston position, the first correction variable and the second correction variable,

[0146] - Determining or calling from a data memory a step reference volume associated with a subsequent movement step of the pipetting piston,

[0147] - Comparing the estimate and the step reference volume with each other,

[0148] - Determining a desired step movement volume for displacing the pipetting piston in a subsequent movement step of the pipetting piston,

[0149] - Displacing the pipetting piston by the desired step movement volume.

[0150] The working temperature can be known because it occurs as an equilibrium temperature in the second working area during the operation of the pipetting device. However, the method can also have a step of detecting the working temperature in the second working area of the pipetting channel.

[0151] An improvement of the pipetting device described above, which preferably operates according to the mentioned method, is also an improvement of the method according to the present invention, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0152] The present invention will be described in detail below with reference to the accompanying drawings. The drawings show:

[0153] Figure 1 showing an embodiment of the pipetting device according to the present invention at the start of the aspiration method according to the present invention, which is the pipetting method of the present application,

[0154] Figure 2 showing during the pipetting method after a smaller first aspiration progress Figure 1 of the pipetting device,

[0155] Figure 3 showing during the pipetting method after a larger second aspiration progress Figure 1 and Figure 2 of the pipetting device,

[0156] Figure 4 A shows a diagram of the aspiration process according to the present invention, which shows the step reference volume, an estimated value of the volume of the metering liquid to be accommodated in the pipetting channel, and the volume swept by the piston face on the metering side, and

[0157] Figure 4 B shows a diagram of a conventional aspiration process that controls the piston stroke only according to the desired metering liquid volume to be metered. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0158] In Figures 1 to 3 , the pipetting device according to the present invention is generally designated by 10. The pipetting device includes a pipetting channel 12, which is formed by a cylinder 13 as a channel section fixed to the device and a pipetting tip 26 that can be detachably coupled to the cylinder 13. The pipetting channel 12 extends along a channel line K of a channel axis designed as a straight line. A piston 14 is movably accommodated in the pipetting channel 12 along the channel track K.

[0159] The piston 14 includes only for reasons of overview Figure 1There are two end caps 16 with reference signs. Between the end caps, a plurality of permanent magnets 18 (three permanent magnets 18 in this example) are accommodated. In order to achieve a clearly separated magnetic field along the channel line K, the permanent magnets 18 are polarized along the channel axis K and are arranged in pairs with like magnetic poles facing each other. From this arrangement, a magnetic field starting from the piston 14 is obtained, which magnetic field has an approximately identical shape around the channel axis K, that is, is substantially rotationally symmetric about the channel axis K, and which magnetic field has a high gradient of magnetic field strength along the channel axis K, such that the differently polarized regions are clearly separated and alternately alternate along the channel line K. Thereby, for example, a high position resolution can be achieved when detecting the position of the piston 14 along the channel axis K by means of a Hall sensor 19, and a very effective coupling of an external magnetic field to the piston 14 can be achieved.

[0160] The end caps 16 are preferably formed of a low-friction material including graphite, as is known, for example, a commercially available piston from the company Airport Corporation in Norwalk, Connecticut, USA. In order to be able to make the most complete use of the low friction provided by the material as much as possible, the cylinder 13 is preferably configured as a glass cylinder, such that when the piston 14 moves along the channel axis K, the material including graphite slides on the glass surface with extremely low friction.

[0161] The piston 14 thus forms the rotor of a linear motor 20, the stator of which is formed by coils 22 (only four coils are shown here by way of example) surrounding the pipetting channel 12.

[0162] It should be clearly pointed out that Figures 1 to 3 Only a roughly schematic longitudinal sectional view of the pipetting device 10 according to the invention is shown, which pipetting device is in no way to be understood as being to scale. In addition, most components are shown by an arbitrary number of components, such as, for example, three permanent magnets 18 and four coils 22. In fact, both the number of permanent magnets 18 and the number of coils 22 can be greater than or also less than the number shown.

[0163] The linear motor 20, more precisely its coils 22, is controlled via a control device 24, which is connected to the coils 22 in the form of a transmission signal. A transmission current is also suitable as a signal to energize the coils and thereby generate a magnetic field through the coils. The control device 24 obtains a pressure detection signal representing the pressure of the working gas 34 in the pipetting channel 12 from a pressure sensor 38, a position detection signal representing the position of the pipetting piston 14 from a Hall probe 19, and a temperature detection signal representing the temperature of the working gas 34 in a second working region AB2 of the pipetting channel 12, which will be described below, from a temperature sensor 23. The temperature sensor 23 is covered by the pipetting piston 14 in Figure 1 and only inFigure 2 and Figure 3 is visible in

[0164] A pipetting tip 26 is detachably arranged in a known manner on the end 12a on the metering side of the cylinder 12. The connection of the pipetting tip 26 to the longitudinal end 12a on the metering side of the cylinder 12 is also only shown schematically in a rough manner.

[0165] The pipetting tip 26 defines a pipetting chamber 28 inside it, and the pipetting chamber can only be accessed through a pipetting opening 30 at the decoupled longitudinal end 26a.

[0166] In Figures 1 to 3 the example of the aspiration process shown, a certain amount 31 of metering liquid 32 is accommodated in the pipetting chamber 28. In Figure 1 the operating state of the pipetting device 10 at the start of the aspiration process is shown, in which the pipetting channel 12 just touches the liquid level 32a of the metering liquid reservoir 40 with the pipetting tip 26 and its pipetting opening 30, so that the working gas 34 is sealed between the pipetting opening 30 and the piston face 14a on the metering side. In this example, the piston face 14a on the metering side is formed by the end cap 16 (relative to the channel line K) pointing in the axial direction to the end face of the metering opening 30.

[0167] In the "air displacement" pipetting method considered here, there is always a working gas 34 between the piston 14 and the metering liquid 32, and the working gas is used as a force medium between the piston 14 and the metering liquid 32.

[0168] In Figure 1 the operating state shown, the working gas 34 with a working gas dead volume V T is sealed between the piston face 14a on the metering side and the pipetting opening 30 closed by the metering liquid 32. In the initial state of the pipetting device 10 for the subsequent aspiration process, the piston face 14a on the metering side is preferably at the bottom dead center. In this bottom dead center, the piston face 14a on the metering side is in a first working region AB1, and the first working region extends from the pipetting opening 30 to the axial starting point of the linear motor 20. In this first working region AB1, the pipetting channel 12 is directly wetted by the ambient atmosphere radially outside, so that the temperature T AB1 of the working gas 34 sealed in the first working region AB1 ∞ constantly corresponds to the ambient temperature T Figure 1 Since the pipetting chamber 28 can only communicate with the ambient atmosphere immediately before the pipetting opening 30 is placed on the liquid level 32a of the metering liquid 32, the pressure p AB1 of the working gas 34 sealed in the operating state of the pipetting device 10 in ∞ is the ambient pressure p Figure 1The pipetting device 10 is shown in a reference state during a subsequent aspiration process. The parameter values mentioned are thus reference values.

[0169] In terms of design, the second working area AB2 is axially connected to the first working area AB1, and the second working area extends axially over the length of the arrangement of the linear motor 20 or its coil 22. The energizable coil 22 for driving the pipetting piston 14 along the channel line K is a heat source which, during operation, causes a temperature T in the interior of the pipetting channel 12 in the second working area AB2 along its extension, i.e. along the second working area AB2 AB2 relative to the temperature T in the first working area AB1 AB1 to increase. The increased temperature T in the second working area AB2 AB2 is either detected by means of the temperature sensor 23 shown in Figure 2 and Figure 3 or is known because of a constantly increasing equilibrium temperature T occurring during continuous operation of the pipetting device 10. AB2 is known.

[0170] The parameters relating to the metering of the liquid 32 and the materials required for its aspiration and dispensing are unknown.

[0171] Based on Figure 1 the initial situation, a predetermined amount of metering liquid 32 is to be aspirated into the pipetting channel 12. For this purpose, the pipetting piston 14 moves along the channel line K in the aspiration direction, i.e. away from the pipetting opening 30, with a step frequency between 100 Hz and 50,000 Hz. The movement is controlled by the control device 24.

[0172] The control device 24 queries the ambient pressure and the ambient temperature via a manual input, a network-supported data query or via other sensors not shown specifically. In addition, the control device 24 reads the number of pipetting piston movement steps stored in the data memory of the control device 24, preferably related to the desired metering liquid amount to be aspirated. Alternatively, the number of pipetting piston movement steps can also be calculated by the control device 24 by means of a formula or entered manually into the control device.

[0173] Based on the known desired metering liquid volume to be aspirated, the control device obtains a step reference volume, either as an incremental step reference volume or as an accumulated step reference volume, by querying a correspondingly filled data memory or by calculation according to a formula for each pipetting piston movement step. Starting from the piston position at the beginning of the pipetting piston movement step, the incremental step reference volume should be traversed given the size of the piston face 14a on the metering side. The accumulated step reference volume indicates the end position at the end of the pipetting piston movement step given the size of the piston face 14a on the metering side. Initialize the step correction movement volume as a correction value, for example, initialize it with the value 0.

[0174] The piston face 14a on the metering side is displaced away from the pipetting opening 30 by a desired step movement volume corresponding to the sum of the step reference volume for the movement step and the step correction movement volume for the movement step by means of a corresponding energization of the coil 22 in the first pipetting piston movement step. Since the step correction movement volume for the first step has an exemplary initialization value of 0, the desired step movement volume is the step reference volume in this case.

[0175] Since the pipetting piston movement step starts from the initial position of the piston face 14a on the metering side and is completely within the first working area AB1 of the pipetting channel 12, the state change of the enclosed working gas 34 caused by the movement of the piston face 14a on the metering side is regarded as an isothermal state change.

[0176] Detect the pressure p of the enclosed working gas 34 via the pressure sensor 38 AB1 , and this pressure is less than the initial ambient pressure p due to the realized piston movement ∞ .

[0177] Estimate the amount of metering liquid V present in the pipetting channel 12 after the first pipetting piston movement step as an estimated volume by means of the above equation 10' (or via the above equation 11 when leakage losses are to be considered) with the known V corresponding to the first step reference volume in this case, and due to the specific movement of the piston face in the first working area (where Kolben V AB2 = 0), and by means of the measured pressure p of the enclosed working gas 34 Kolben . AB1 liquid

[0178] Form a difference by means of the step reference volume and the estimated volume V, for example, form the difference by subtraction. The difference indicates the numerical difference between the step reference volume and the estimated volume V liquid . liquid

[0179] Based on the difference, the stepping correction movement volume is calculated as a correction value by basically known PID regulation, and the subsequent pipetting piston movement step's stepping reference volume is corrected to the desired stepping movement volume by means of the correction value. For this purpose, the difference is converted into the stepping correction movement volume by means of a proportional conversion term, a differential conversion term, and an integral conversion term. The individual conversion terms can be weighted by experimentally determined weighting factors.

[0180] The counter for the pipetting piston movement step is incremented by 1, and if the maximum number of pipetting piston movement steps has not yet been reached, then the stepping reference volume associated with the next pipetting piston movement step is considered and corrected to the desired stepping movement volume by means of the previously determined stepping correction movement volume, for example by summation or subtraction. The piston face 14a on the metering side then moves corresponding to the desired stepping movement volume taking into account its area size, that is, the desired stepping movement volume is divided by the numerical size of the piston face 14a on the metering side to obtain the displacement path of the piston face 14a along the piston line K.

[0181] Then, as described above, the pressure p of the enclosed working gas 34 is detected again AB1 , and according to Equation 10' (or according to Equation 11 when leakage losses are to be considered) by means of the known V Kolben (where always AB2 V Kolben = 0), and by means of the measured pressure p of the enclosed working gas 34 AB1 the amount of metering liquid V present in the pipetting channel 12 after the pipetting piston movement step is realized is estimated liquid .

[0182] The described formation of the difference between the stepping reference volume and the estimated value V liquid and the described calculation of another stepping correction movement volume based on this are carried out again. The said another stepping correction movement volume is in turn used to obtain the next desired stepping movement volume. Then the increment of the stepping counter and the renewed movement of the piston face 14a on the metering side are carried out.

[0183] The said sequence runs iteratively in the described manner until the piston face 14a on the metering side reaches the boundary between the first working area and the second working areas AB1, AB2, such that the further movement of the piston face 14a no longer takes place in the first working area AB1 but in the second working area AB2.

[0184] If the piston face 14a on the metering side moves in the second working area AB2 such that the movement of the piston face 14a causes the enclosed working gas 34 to move between the first working area AB1 and the second working area AB2, then the process described above remains basically unchanged. However, in the equations 10, 10', 10", or 11 that can be used to determine the estimated value V liquid above, the AB2 current value of V Kolben that is then different from 0 is used. Thus, in addition to the pressure change, the movement of the working gas fraction between the first working area AB1 and the second working area AB2 and its temperature change are also considered.

[0185] That is to say, the piston face 14a on the metering side is moved again according to the finally calculated desired stepped movement volume. Then, the pressure p AB1 of the enclosed working gas 34 is detected by the pressure sensor 38, and the temperature T AB2 of the working gas in the second working area AB2 is detected by the temperature sensor 23. AB1 The temperature T ∞ of the working gas in the first working area AB1 continues to be assumed to be constant and is considered to be equal to the ambient temperature T

[0186] for the considerations mentioned above. liquid Subsequently, an estimated value V of the volume of the metering liquid 32 accommodated in the pipetting channel 12 is determined based on the detected parameters using one of the equations 10, 10', 10″, or 11.

[0187] The difference is determined by comparing the estimated value with the stepped reference volume associated with the current pipetting piston movement step, and the stepped correction movement volume is obtained based on the difference according to the PID regulation described above and known in terms of its principle. With the stepped correction movement volume, the stepped reference volume is corrected to the desired stepped movement volume.

[0188] If the maximum number of steps of the pipetting process has not been reached after the step counter is incremented, then the next pipetting piston movement step is performed with the desired stepped movement volume as the desired preset for the movement of the piston face 14a on the metering side.

[0189] Advantageously, the curve of the change of the step reference volume over the number of steps of the pipetting piston movement set for the pipetting process is not selected linearly, but decreasingly, that is, the increase in the cumulative step reference volume or the cumulative incremental step reference volume (whichever is applicable) is greater at the beginning of the pipetting process than near the end of the pipetting process. Here, with respect to the larger of the two comparison values, the step reference volume of at least the last 30% of the steps of the pipetting piston movement for the pipetting process changes by no more than 10% numerically. The advantage of the decreasing curve of the step reference volume is that until the end of the pipetting process, the influence of the correction value determined from the difference on the movement of the piston face 14a on the metering side prevails. Thus, near the end of the pipetting process, for example, during the last 30% of the steps of the pipetting piston movement, the influence of the different flow characteristics of the different metered liquids can be compensated by determining the difference and the resulting correction value (step correction movement volume).

[0190] Different metered liquids converge to the desired metered liquid amount at different speeds depending on their pipetting-related influencing factors such as viscosity, density, surface tension, and wetting behavior with respect to the material of the pipetting channel. If the number of steps of the pipetting piston movement is selected large enough, then it can be ensured that metered liquids with a relatively high density and high viscosity can also be pipetted precisely without knowledge of their exact liquid parameters.

[0191] In Figure 4 A, a diagram of the aspiration process as an embodiment of the pipetting process according to the invention is shown. Figure 4 The abscissa of the coordinate system of A represents the time in seconds, i.e., from 0 seconds to 16 seconds. The ordinate represents the volume in microliters (μl), i.e., from -5 μl to 20 μl.

[0192] The desired metered liquid volume to be aspirated is 10 μl. The metered liquid to be aspirated is glycerol.

[0193] The change curve of the step reference volume is shown as a cumulative value using reference numeral 42. Until t = 5 seconds after the aspiration process starts, the cumulative value remains at a value of 0 μl, and then linearly increases from 0 μl to the desired metering liquid volume of 10 μl in the time range from 5 seconds to 10 seconds. Thus, the pipetting process only starts at t = 5 s. In the time range from 10 seconds to 15 seconds, the step reference volume remains at a value of 10 μl, which is the desired metering liquid volume. Thus, the time range from 5 seconds to 10 seconds forms the first step range 44 as described above, in which the cumulative step reference volume increases to at least 95% of the desired metering liquid volume. The range from 10 seconds to 15 seconds forms the second step range 46 as described above, in which the cumulative step reference volume does not deviate from the range of 95% to 105% of the desired metering liquid volume. More precisely, the cumulative step reference volume increases from 0% to exactly 100% of the desired metering liquid volume in the first step range 44 and remains at exactly 100% of the desired metering liquid volume in the second step range 46.

[0194] During Figure 4 A, the volume swept by the end face 14a on the metering side during the pipetting process is plotted using reference numeral 48.

[0195] Starting from the 0 position at the beginning of the pipetting process, the volume swept by the end face 14a on the metering side is initially negative, i.e., the end face 14a on the metering side is closer to the pipetting opening 30 in the dispensing direction to counteract the inflow of glycerol into the pipetting tip 26 caused by capillary forces.

[0196] The volume difference 50 between the volume swept by the end face 14a on the metering side (which actually corresponds to the moving volume of the end face 14a on the metering side and thus to the cumulative desired step movement volume) and the step reference volume is the step correction movement volume calculated as described above.

[0197] The estimated value of the metering liquid volume accommodated in the pipetting channel 12 or the receiving chamber 28, calculated as described above, is denoted by reference numeral 52.

[0198] As Figure 4 shown in A, the movement of the pipetting piston 14 first only corresponds to preventing glycerol from flowing into the pipetting tip 26 capillarily through the preset step reference volume 42.

[0199] If the step reference volume 42 starts to increase numerically at the moment of 5 seconds, the metering liquid first remains below the step reference volume 42. However, if the step reference volume 42 remains constantly at the reached desired metering liquid volume at the moment of 10 seconds, the metering liquid exceeds the step reference volume.

[0200] As already described in detail above, the second step range 46 adjacent to the first step range 44 serves to correct the tendency for overflow or backflow of the metered liquid by a corrective movement of the metering-side end face 14a after approximately the desired metered liquid volume has been roughly received in the receiving chamber 28. Since the vast majority of the desired metered liquid volume has been received in the receiving chamber 28 in the first step range 44, each desired step movement volume in the second step range 46 of the metering-side end face 14a is smaller than in the first step range 44, which overall results in a high metering accuracy of the pipetting process. In the example shown, the second step range 46 lasts approximately as long as the first step range 44, thus including approximately the same number of movement steps of the pipetting piston 14.

[0201] In Figure 4 B is plotted how glycerol behaves during a pure path-time-controlled aspiration movement of the pipetting piston 14 when the pipetting piston 14 is lifted with the desired metered liquid volume taking into account the area of the metering-side end face 14a.

[0202] The abscissa again represents time in seconds, and the ordinate represents volume in μl.

[0203] Figure 4 In B, the desired movement trajectory of the metering-side end face 14a is denoted by the reference numeral 42'. The desired movement trajectory precisely corresponds to Figure 4 the cumulative step reference volume of

[0204] The movement curve of the metering-side end face 14a following the desired movement trajectory 42' in a path-time-controlled manner is denoted by the reference numeral 48'. Since the path-time control of the metering-side end face 14a according to the desired movement trajectory 42' is technically unproblematic, the metering-side end face 14a follows the desired preset very precisely.

[0205] The metered liquid volume received in the pipetting tip 26 is plotted in terms of time with the reference numeral 52'. In Figure 4 the diagram of B, it can be very clearly seen that, without the corresponding paired control by the pipetting piston 14, glycerol, for example, starts to flow into the receiving chamber 28 of the pipetting tip 26 through the pipetting opening 30 in a manner driven only by capillary forces at t = 1 s. At t = 1 s, in both cases, i.e., according to Figure 4 A and Figure 4 B, the pipetting opening 30 is immersed in the metered liquid reservoir 32.

[0206] With the start of the piston movement at time t = 5 s, glycerol also starts to flow further into the receiving chamber 28 of the pipette tip 26, this time being driven by the negative pressure relative to the ambient pressure generated by the piston movement in the working gas 34.

[0207] After the piston movement ends at time t = 10 s, glycerol continues to flow into the receiving chamber 28 through the pipetting opening 30 until the negative pressure in the pipetting channel 12 (and thus in the receiving chamber 28) decreases to such an extent that the negative pressure and the liquid column 29 formed by glycerol in the receiving chamber 28 are substantially in force equilibrium. However, only slightly less than 8 μl of glycerol is received in the receiving chamber 28 thereby, even though the pipetting piston 14, acting as the driver for the glycerol receiver, performs a movement of 10 μl.

[0208] In a conventional pipetting system, the liquid type is stored in the data memory of the control device 24, glycerol is associated with the liquid type, and from the liquid type the following factor is known, by which the desired movement volume of the pipetting piston 14 has to be increased from the desired 10 μl such that the desired 10 μl of glycerol is received in the pipette tip 26 at the end of the piston movement. This factor has to be determined empirically in the laboratory.

[0209] As Figure 4 A Figure 4 shown by the comparison with B, compared to a pipetting piston 14 using a conventional path or path - time - motion control, with the present invention, due to the described volume - based control, it is possible to pipette the desired volume of the desired metering liquid highly precisely and even highly precisely in a shorter time without knowing the liquid type of the metering liquid and without knowing the specific flow characteristics of the metering liquid.

Claims

1. A pipetting device (10) for aspirating and / or dispensing a metered liquid (32) by means of a working gas (34), wherein the pipetting device (10) comprises: - A pipetting channel (12) extending along a channel axis (K), - A pipetting piston (14) movable along the channel axis (K) in the pipetting channel (12), - A receiving chamber (28) for receiving the metering liquid (32), the receiving chamber extending in the pipetting channel (12) along the channel axis (K) from a pipetting opening (30) at one end to a piston face (14a) of the pipetting piston (14) at the other end facing the pipetting opening (30), wherein a working gas (34) is received in the pipetting channel (12) in close proximity to the piston face (14a) of the metering side, wherein the working gas reference volume (V T ) is defined by the volume of the working gas (34) in the receiving chamber (28) below the working gas reference pressure (p ∞ ), - A drive device (20) coupled to the pipetting piston (14) in a force-transmitting manner, the drive device being configured to displace the pipetting piston (14) along the channel axis (K), - A position detection device (19) that detects the position of the pipetting piston (14) along the channel axis (K) and outputs a position detection signal representing the detected position, - A pressure detection device (38) that detects the pressure of the working gas (34) in the pipetting channel (12) and outputs a pressure detection signal representing the detected pressure, and - A control device (24), wherein the control device (24) is configured to control the drive device (20) in accordance with the following, taking into account changes induced by pressure changes caused by the piston movement in the reference volume (V T ) of the working gas: - The pressure detection signal, - The reference pressure of the working gas (p ∞ ), and - A defined desired metered liquid volume to be aspirated, wherein the control device (24) is further configured to perform piston movements required for aspirating the desired metered liquid volume in a plurality of successive movement steps, characterized in that the pipetting channel (12) has: a first working region (AB1) having a known base temperature in a lower base temperature range; and a second working region (AB2) having a known working temperature in a working temperature range elevated relative to the base temperature range, wherein the control device (24) is configured to, for subsequent pipetting piston movement steps after a first pipetting piston movement step, - Based on the position detection signal, the pressure detection signal, and the working gas reference pressure (p ∞ ), a first correction variable is obtained, where the first correction variable represents the volume change induced by the pressure change of the portion of the working gas volume enclosed in the pipetting channel (12) that is in the first working region (AB1), and -Derive a second correction variable based on the position detection signal, the pressure detection signal, the reference pressure (p ∞ ) of the working gas, the known working temperature, and the known basic temperature, where the second correction variable represents the volume change induced by pressure change and temperature change of the portion of the working gas volume enclosed in the pipetting channel (12) that is in the second working region (AB2). and based on - A step reference volume associated with the subsequent pipetting piston movement step, - The hitherto displaced volume (V Kolben ) of the piston face (14a) on the metering side of the pipetting piston (14) during the current pipetting process - The first correction variable, and - The second correction variable, to determine a desired step movement volume of the pipetting piston (14), and to control the drive device (20) according to the determined desired step movement volume.

2. The pipetting device (10) according to claim 1, Characterized in that, The control device (24) is configured to, for subsequent pipetting piston movements in steps, determine an estimated value (V Kolben ) for the liquid column (29) present in the receiving chamber (28) based on the hitherto displaced volume (V liquid ) of the piston face (14a) on the metering side of the pipetting piston during the current pipetting process, the first correction variable, and the second correction variable, compare the determined estimated value (V liquid ) with the step reference volume, and determine the desired step movement volume based on the comparison result.

3. The pipetting device (10) according to claim 2, Characterized in that, The control device (24) is configured to perform successive pipetting piston movement steps until the difference between the determined estimated value and the step reference volume is less than a predetermined difference threshold.

4. The pipetting device (10) according to claim 2, It is characterized in that The control device (24) is configured to perform a predetermined number of pipetting piston movement steps.

5. The pipetting device (10) according to any one of claims 2 to 4, It is characterized in that The control device (24) is configured to calculate the difference between the determined estimated value (V liquid ) and the step reference volume, and to determine a share of the step correction movement volume proportional to the difference and / or an integral share of the step correction movement volume taking into account the sum of the difference and at least one previous difference and / or a differential share of the step correction movement volume taking into account the difference between the difference and the previous difference.

6. The pipetting device (10) according to claim 5, Characterized in that, The control device (24) is configured to determine the desired step movement volume based on the step reference volume and the step correction movement volume.

7. The pipetting device (10) according to claim 6, It is characterized in that The control device (24) is configured to determine the desired step movement volume as the step reference volume corrected by the step correction movement volume.

8. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that The control device (24) is designed to execute more than 100 pipetting piston movement steps per second, wherein the control device is designed to execute less than 100,000 pipetting piston movement steps per second.

9. The pipetting device (10) according to claim 8, It is characterized in that The control device (24) is designed to execute more than 1000 pipetting piston movement steps per second.

10. The pipetting device (10) according to claim 8, Characterized in that, The control device (24) is designed to execute more than 10,000 pipetting piston movement steps per second.

11. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that, The control device (24) is designed to read the step reference volume associated with the subsequent pipetting piston movement step from a data memory as a function of the desired metered liquid volume and / or to calculate the step reference volume based on the desired metered liquid volume.

12. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that - the step reference volume is an incremental step reference volume, wherein the cumulative value of the step reference volume has a first step range (44) over an increasing number of steps, in which the cumulative value increases from an initial value to a value of at least 95% of the desired metered liquid volume, and the cumulative value has a second step range (46) following the first step range (44), in which the cumulative value does not deviate from the range of 95% to 105% of the desired metered liquid volume, or - the step reference volume is an absolute step reference volume, wherein the value of the absolute step reference volume has a first step range (44) over an increasing number of steps, in which the value of the absolute step reference volume increases from an initial value to a value of at least 95% of the desired metered liquid volume, and the value has a second step range (46) following the first step range (44), in which the value of the absolute step reference volume does not deviate from the range of 95% to 105% of the desired metered liquid volume, The second stepping range (46) has at least the same number of steps and / or continues for at least the same duration as the first stepping range.

13. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that The control device (24) is designed to define the ascertained desired step movement volume by quantifying at least two of the following three parameters: - the desired end position of the piston face (14a) on the metering side at the end of the subsequent pipetting piston movement step, - the desired displacement speed of the piston face (14a) on the metering side during the subsequent pipetting piston movement steps, and - the duration of said subsequent pipetting piston movement step.

14. The pipetting device (10) according to any one of claims 1 to 4, Characterized in that, The control device (24) is configured to form the second correction variable based on a product of a partial amount of the working gas (34) in the second working region (AB2) and a product of a pressure quotient and a temperature quotient, where the pressure quotient is a quotient formed by the detected working gas pressure (p AB1 ) and the working gas reference pressure (p ∞ ), and where the temperature quotient is a quotient formed by the working temperature (T AB2 ) and the base temperature (T ∞ ).

15. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that wherein the drive device (20) comprises a linear motor, the rotor of which is the pipetting piston (14), and wherein the drive device (20) comprises a plurality of energizable coils (22) which are arranged radially outside the pipetting channel (12) along a drive section, and wherein the second working area (AB2) comprises or is the drive section.

16. The pipetting device (10) according to any one of claims 1 to 4, Characterized in that, wherein the first working area (AB1) extends from the pipetting opening (30) towards the pipetting piston (14).

17. The pipetting device (10) according to claim 16, It is characterized in that wherein the first working area (AB1) extends from the pipetting opening (30) towards the pipetting piston (14) up to the second working area (AB2).

18. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that The pipetting device (10) has a temperature sensor (23) for detecting the operating temperature (T AB2 ), and the temperature sensor outputs an operating temperature signal representing the operating temperature (T AB2 ).

19. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that wherein the pipetting channel (12) comprises a device-fixed channel section (13) having a coupling assembly and a pipetting tip (26) detachably coupled to the coupling assembly, and wherein the pipetting tip (26) has the pipetting opening (30).

20. The pipetting device (10) according to any one of claims 1 to 4, It is characterized in that wherein the control device (24) is configured to determine a third correction variable which represents a leak in the pipetting channel (12), and wherein the control device (24) is configured to additionally determine the desired step movement volume of the pipetting piston (14) based on the third correction variable.

21. The pipetting device (10) according to claim 20, Characterized in that, wherein the third correction variable represents a leak volume, and wherein the control device (24) is configured to determine the third correction variable based on the pressure detection signal and the duration.

22. The pipetting device (10) according to claim 21, It is characterized in that wherein the duration is the duration of a step of the pipetting piston movement.

23. The pipetting device (10) according to claim 20, It is characterized in that, wherein the control device (24) is configured to also determine the third correction variable based on a leak parameter, and wherein the control device (24) is further configured to determine the leak parameter in accordance with a manual control input or by a predefined automated control when performing a detection of a time change of an initially defined working gas pressure caused by the leak.

24. The pipetting device (10) according to claim 21, It is characterized in that wherein the control device (24) is configured to also determine the third correction variable based on a leak parameter, and wherein the control device (24) is further configured to determine the leak parameter in accordance with a manual control input or by a predefined automated control when performing a detection of a time change of an initially defined working gas pressure caused by the leak.

25. A method for correctly aspirating the metering liquid (32) by means of the pipetting device (10) according to any one of the preceding claims, independently of the flow characteristics and / or wetting characteristics of the metering liquid (32), wherein the pipetting channel (12) has: a first working area (AB1), the known basic temperature (T ∞ ) being in a lower basic temperature range; and a second working area (AB2), the known working temperature (T AB2 ) being in a working temperature range increased relative to the basic temperature range, wherein the method performs a stepwise displacement of a pipetting piston (14) movably received in the pipetting channel (12), and wherein, after a first movement step of the pipetting piston (14), for subsequent movement steps of the pipetting piston, the method comprises the following method steps: - Detect the pressure (p AB1 ) of the working gas (34) - Detecting the position of the pipetting piston, - Based on the detected pipetting piston position, the detected working gas pressure (p AB1 ), and the working gas reference pressure (p ∞ ), a first correction variable is obtained, where the first correction variable represents the volume change induced by the pressure change of the first part of the volume of the working gas (34) sealed in the pipetting channel (12) that is in the first working region (AB1). - Based on the detected pipetting piston position, the detected working gas pressure (p AB1 ), the working gas reference pressure (p ∞ ), the known working temperature (T AB2 ) and the known base temperature (T ∞ ), a second correction variable is determined, which represents the volume change induced by pressure change and temperature change of the portion of the working gas (34) enclosed in the pipetting channel (12) that is in the second working region (AB2). -Determine an estimate value (V liquid ) for the metering liquid (32) present in the receiving chamber (28) based on the detected pipetting piston position, the previous pipetting piston position, the first correction variable, and the second correction variable - Obtain or call from a data memory a step reference volume associated with the subsequent pipetting piston movement step, - Compare the estimated value (V liquid ) with the step reference volume. - Determine a desired step movement volume for displacing the pipetting piston in the subsequent pipetting piston movement step, - Displace the pipetting piston (14) by the desired step movement volume.

26. The method according to claim 25, It is characterized in that The method further comprises the following additional steps: - Detect the operating temperature (T AB2 ) in the second working area (AB2) of the pipetting channel (12).

Images