Patent Grant
12345722
This application claims priority to European Patent Application No. 24172380.8 filed Apr. 25, 2024, the entire contents of which are hereby incorporated by reference.
The invention relates to the field of handling liquid and solid substances more particular to a method of calibrating aspired volumes of liquids and/or solid substances. The invention relates also to a volume calibration device and a system configured to calibrate the volume of aspired substances, such as liquids, and a system which is suitable to carry out the method.
The precise measurement of the volume of aspired and/or dispensed liquid, solid or gaseous substances is important in several fields, in particular in the field of chemistry and biology in which the aspired volumes are most of the time small, typically less than 1000 μl. Today's standard calibration methods for laboratory suction devices, such as pipettes, is mainly based on a gravimetrical method which comprises the precise weighting of the dispensed liquid by the laboratory precision scale. The majority of pipettes on the market have full range displacement comprised 10 μl and 1000 μl. Most common categories are 10 μl, 20 μl, 100 μl, 200 μl and 1000 μl.
Alternatively, calibration of liquid dispenser can be performed using the principle of dilution of a colored or fluorescent solution into a known volume of water. The dilution methods require the use of well-characterized test solutions and known and precise volume of solvent sample. It also requires a very accurate optical sensing device that needs itself regular calibration.
The specifications of laboratory liquid handling devices, such as pipettes, are guided by the norm ISO 8655. This norm imposes a systematic error typically below 1% of displacement and a random error below 0.4% for maximal range of the pipette. These error values can be higher for small volumes. The required precision for the measurement of volumetric displacement is in the order of 0.1 μl. This imposes (density of water) an accuracy of 0.1 mg in weighting the substance, typically a liquid. The calibration process requires: 1) an accurate scale, 2) compensation of errors due to temperature, 3) avoiding evaporation of liquid and 4) a series of very careful manipulations.
The users of laboratory pipettes, depending on their accuracy constraints, must regularly check and calibrate their pipettes. As the calibrations need specific skills, the users often subcontract this task to external service providers. The cost of calibration is therefore a non-negligible part of the cost of ownership of laboratory pipettes.
The majority of existing or disclosed products are based on laboratory scales and require very careful handling and weighting of liquids. There exist at least two products called “pipette testers” that are based on the measurement of the leak rate when the pipette is pressurized and which are described in the following internet references 1-2:
The leak checking allows the rejection of leaky pipettes, but is not a measurement of the volumetric precision, as it is required by the ISO 8655. Therefore, the gravimetric calibration method is still needed to qualify the pipettes.
The document US2012/0240663 describes a method for leak-testing hand-held piston strike pipettes and an associated leak-testing apparatus. The system and method described in US2012/0240663 allows to detect leakage in single-channel and multi-channel piston stroke pipettes by using a pressure sensor and a vacuum pump and consist in measuring pressure raise after stopping or disconnecting the vacuum pump, the system and method does not provide a solution for measuring accurately the aspired volumes by the pipettes.
The document U.S. Pat. No. 3,962,916 describes a complicated system comprising a plurality of electronic controlled fluidic gates for the measurement of a closed air space but would be unsuitable to calibrate precisely a small volume of an aspired liquid. It is based on the use of a regulated gas supply that is needed to generate a reference pressure.
Document U.S. Pat. No. 8,561,459 describes a volume gauge comprising a chamber comprising a pressure changing device coupled to said chamber. The pressure changing device is configured to change a pressure and to measure a gas pressure of air located in the chamber. A processor having a memory stored with the total volume of the chamber and a reference pressure corresponding to an empty chamber is provided. Based on received pressure measurement data, the processor may determine the percentage volume occupied by a solid or liquid substance. Although the system disclosed in US2012/0240663 allows determining approximately the volume of a solid or liquid substance, the system is not very fast and is not accurate and may achieve at best a precision of about 1%. Also, the system is complex as requiring a pressure control system. Furthermore, in order to achieve higher accuracies, the system of US2012/0240663 would need a compensation correction for temperature variations. Also, evaporation of the liquid may be an additional source of inaccuracy.
Therefore, a better system than the ones available from prior art is required. The system should be simpler, cheaper and faster and be more reliable than existing devices. Furthermore, the precision should be at least as good or better than the precision of known liquid weighting method, which is the reference method used in the ISO standard.
There is also a requirement to be able to determine volumetric effects due to some parts of a calibration system such as the use of valves. It is also desirable to provide a system that allows to take into account effects due to hydrostatic pressure in an aspiration system.
Additionally, there is a need for a new system so that the user can easily perform calibration as often as desired without the need of a precise scale and possibly without liquid or sample solution. The new system should also be adaptable to test, in parallel, a plurality of aspiration systems during the same calibration procedure.
A new method and system should reduce the cost of ownership of laboratory pipettes and increase quality control because of its ease of use. None of the cited requirements can be achieved by existing or disclosed precise volume measurement systems.
The invention proposes a new liquid handler calibration method and a system, configured to calibrate the volume of aspired and/or dispensed substances, such as liquids, which solve the limitations of devices and calibration methods of prior art. The calibration method and device does not require liquid sample handling and is based on the measurement of gas displacement volume through the pressure change inside a closed volume. Available barometric pressure sensors have an absolute accuracy below 0.1 mbar and a short-term repeatability below 0.02 mbar. As the relative change of pressure is equal to the relative change volume, typical 0.1% absolute accuracy can be reached in displacement measurements.
The gas volume calibration method is at least as accurate as existing liquid weighting methods but it is much simpler and much faster and cheaper. Moreover, there is no need to compensate for temperature variation effects and the system does not need to avoid evaporation. Contrary to known weighting calibration techniques the user can easily perform calibration as often as desired without the need of a precise scale. In addition, as the system uses no liquid, the user can verify the functionality of the pipette and tip prior to a given measurement. The new method of the invention reduces the cost of ownership of for example laboratory pipettes and increases the quality control because of its ease of use. In addition, the method allows e.g. the detection and characterization of pipetting failure and the need of seal replacement in liquid handler devices such as pipetting devices.
The invention is achieved by the device, system and method as described in the claims.
The calibration system and method of the invention allow to take into account the volumetric effects due to the use of valves in the calibration system. Furthermore, the system allows to take into account effects due to hydrostatic pressure in an aspiration system. In embodiments, the system and method of the invention allow to calibrate, in parallel, a plurality of aspiration systems during the same calibration procedure.
Further details of the invention will appear more clearly upon reading the following description in reference to the appended figures:
The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to the practice of the invention.
It is to be noticed that the term “comprising” in the description and the claims should not be interpreted as being restricted to the means listed thereafter, i.e., it does not exclude other elements.
Reference throughout the specification to “an embodiment” means that a particular feature, structure or characteristic described in relation with the embodiment is included in at least one embodiment of the invention. Thus appearances of the wording “in an embodiment”, or, “in a variant”, in various places throughout the description, are not necessarily all referring to the same embodiment, but several. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a skilled person from this disclosure, in one or more embodiments. Similarly, various features of the invention are sometimes grouped together in a single embodiment, figure or description, for the purpose of making the disclosure easier to read and improving the understanding of one or more of the various inventive aspects. Furthermore, while some embodiments described hereafter include some, but not other features included in other embodiments, combinations of features if different embodiments are meant to be within the scope of the invention, and from different embodiments. For example, any of the claimed embodiments can be used in any combination. It is also understood that the invention may be practiced without some of the numerous specific details set forth. In other instances, not all structures are shown in detail in order not to obscure an understanding of the description and/or the figures.
In a first aspect, the invention is achieved by a volumetric displacement calibration device 1 comprising at least one opening 3 configured to be able to adapt at least one suction system 1000, comprising a tip 1006, having a volume VP, connected to a shaft 1003 comprising a volume changing mechanism 1002 arranged to be movable between a distal position Z0 and a proximal position Z1, the proximal position Z1 being closer to said opening 3 than said distal position Z1. In an embodiment said least one suction system 1000 is a pipette and the volume changing mechanism 1002 is the piston of that pipette.
The shaft 1003 is typically an elongated tube defining a Z-axis. The negative sense of the Z-axis is defined as the sense from said distal position Z0 to said proximal position. The shaft 1003 has an internal volume that may be reduced to a remaining volume of air 1005 when the volume changing mechanism 1002 is pressed down, as illustrated in
The volumetric displacement calibration device 1 of the invention comprises:
The volumetric displacement calibration device 1 is characterized in that it comprises:
The determination of the parameter Vo is essential to the invention. This parameter Vo has the dimension of a volume and allows to provide the required calibration of the aspired volumes in the suction systems as described herein, such as pipettes.
Also, the determination of the parameter Vo is essential for determining leaks and/or to determine a compensation for hydrostatic pressures as will be described further.
The parameter Vo is defined as an internal volume and is the sum of the following 3 volumes:
Such defined internal volume Vo is determined by:
Vo=Vref*(P2−Pc)/(P1−P2) wherein Pc=P00+(P0y−P00y).
In an embodiment, said volumetric displacement calibration device 1 comprises second calculation means designed to be able to calculate a calibrated displacement volume dV of the suction system 1000. This calibrated displacement volume dV is determined by:
dV=Vo*(P1−P0)/P0.
In an embodiment, intended to determine volume leaks of the volumetric displacement calibration device 1, the first pressure sensor 12 is arranged to be able to measure a pressure P11 at a predetermined time t after the measurement of P1 and before opening the valve 102. In such an embodiment, the volumetric displacement calibration device 1 comprises third calculation means designed to be able to calculate a volume leak F of the device 1. The volume leak F is determined by:
F=Vo*(P1−P11)/(P0*t).
In an advantageous embodiment, the volumetric displacement calibration device 1 is configured to be able to adapt n suction systems 10001, 10002, . . . , 1000k, 1000n-1, 1000n, and comprises:
As will be described further, a volumetric displacement calibration system 2 defines a plurality of system channels C1-Cn. One of the system channels is predetermined as the key system channel Ck. Each comprises a main chamber 101, 102, . . . , 10k, . . . , 10n-1, 10n. However, there is, in such a system 2, only one channel that is defined as a key channel Ck, which is the only channel in the system 2 that comprises said reference chamber 20, as illustrated in
More precisely, in said embodiment wherein the volumetric displacement calibration device 1 is configured to be able to adapt n suction systems 10001, 10002, . . . , 1000k, . . . , 1000n-1, 1000n, only one of the n main chambers 10-10n is connected to said reference chamber 20 by a conduct 100. Any main chamber 10-10n of the n chambers may be chosen to be used as the main test chamber 10 and be connected to the unique reference chamber 20 of the calibration device 1. The main test channel 10k is defined as the k'th main chamber, k being chosen among any predetermined number from 1 to n.
In the embodiment illustrated in
In said embodiment comprising n identical main chambers, said second calculation means allow to determine a parameter Vok which has the dimension of a volume and defined as an internal volume and is the sum of the volume VPk of the tip of the k'th suction system 1000k, the residual volume of the shaft when the volume reduction mechanism 1004 is in the proximal position Z1 and the volume of the test chamber 10k, and determined by:
Vok=Vref*(P2k−Pck)/(P1k−P2k),
Similar to the embodiment of a single channel as described before, Vok is a parameter that is defined as an internal volume defined for said key channel Ck of the system 2, and is the sum of the following 3 volumes:
In an embodiment, said volumetric displacement calibration device 1 comprises second calculation means designed to be able to calculate a calibrated displacement volume dVk of the suction system 1000 in said channel Ck. This calibrated displacement volume dVk is determined by:
dVk=Vok*(P1k−P0K)/P0K
In said embodiment, in which all main chambers 101, 102, . . . , 10k, . . . , 10n-1, 10n in the device 1 have the same volume, the displacement volumes dVi of all the n suction systems 1000-1000n is given by:
dVi=Vok*(P1i−P0i)/P0i, wherein 1≤i≤n.
In an embodiment in which not all volumes of the main chambers 101, 102, . . . , 10k, . . . , 10n-1, 10n are identical, the difference Δi of volumes of main chambers of all channels C1-Cn, referred to the test channel Ck are taken into account and are provided in a first lookup table.
The volume displacements dVi in each channel C1-Cn is computed by said second calculation means, and is determined as:
dVi=(Vok−Ai)*(P1i−P0i)/P0i, wherein 1≤i≤n.
Herein Δi, 1≤i≤n, is given by said first lookup table, illustrated in table 1, comprising the differences Δi of the internal volumes of the n−1 main chambers 101-10n, relative to the volume of said test chamber 10, being the k'th chamber in the embodiment of
The pressure P1i is the pressure measured in the i-th main chamber 101-10n, wherein 1≤i≤n, when the volume change mechanism 1004 is in said proximal position Z1 and the valve 102 closed.
The pressure P0i is the pressure measured in the i-th main chamber 101-10n, wherein 1≤i≤n, when the volume change mechanism 1004 is in the distal position Z1 and the valve 102 closed.
In variants, the n main chambers 101-10n may be arranged in a linear configuration, in the X or Y direction or in a 2D configuration, i.e. in an X-Y plane.
In embodiments, said n first pressure sensors 121-12n, connected to the other n−1 chambers, are arranged to measure a pressure P11i wherein 1≤i≤n, measured at a predetermined time t after the measurement of P1i, wherein 1≤i≤n and before opening the valve 102. In such embodiments intended to determine leaks, said third calculation means are designed to be able to calculate the volume leaks Fi of the device 1, wherein 1≤i≤n.
In embodiments wherein all the main chambers 10-10n have the same volume the leaks Fi are determined by:
Fi=Vok*(P1i−P11i)/(P0i*t), wherein 1≤i≤n.
In embodiments wherein all main chambers 101-10n may have different volumes, the leaks Fi are determined by:
Fi=(Vok−Ai)*(P1i−P11i)/(P0i*t), wherein 1≤i≤n.
In embodiments, the volumetric displacement calibration device 1 takes into account the liquid height that induces a hydrostatic pressure due to liquid column height. This is useful If other tips than those used during the gravimetric (or dilution) calibration are used, as the effective delivered volume will deviate for the calibrated value. For a same quantity of liquid that is aspirated in the tip, the height reached by the liquid will, for example, be higher in a long and narrow tip than in short tip, both tips having the same nominal volume. This liquid height induces a hydrostatic pressure due to liquid column height and therefore induces a small, but not negligible, offset dVc between the effective aspirated volume VL and the true displacement volume of the piston of the pipette.
In such an embodiment, the calibration device 1 comprises a second look-up table which contains the information of the liquid heights hi for different models of aspiration tips 1006 and for each defined liquid volume VL to be tested. In such an embodiment, the volumetric displacement calibration device 1 comprising fourth calculation means that are designed to be able to calculate a volumetric compensation Vci of the gravimetric effect, for all of the aspiration tips.
The volumetric compensation Vci of the gravimetric effect is determined by knowing the parameter Vo and by taking into account said second look-up table h(a,b). Such a second lookup table has two dimensions: tip models and the test volumes, in percentage of the nominal tip volumes.
In the table h(a,b), a is the nominal volume of the pipette and b the tested volume. The values of b and y are entered by the user into a test machine before performing a calibration.
In an embodiment of a system 2 with a single test channel, the volumetric compensation Vc of the gravimetric effect is determined by:
Vc=−h(a,b)*w*g*Vo/P0,
The displaced volume is the determined by:
VL=dV−Vc.
In an embodiment of a system 2 with a plurality of test channels C1-Cn, the volumetric compensation Vc of the gravimetric effect is determined by:
Vli=dVi−Vc, wherein 0≤i≤n.
In another aspect, the invention is also achieved by a volumetric displacement calibration system 2 that comprises at least one volumetric displacement calibration device 1, as described herein, and at least one suction system 10001, 10002, . . . , 1000k, . . . , 1000n-1, 1000n adapted to said at least one volumetric displacement calibration device 1. The suction systems 10001-1000n are preferably pipettes but not necessarily so.
In an embodiment, illustrated in
In another aspect, the invention is also achieved by a method for calibrating a volumetric fluid handling system 2 and comprises successive steps (a-l), consisting of:
In an advantageous embodiment, the method comprises a step m) of determining the calibrated displacement volume dV, calculated by dV=Vo*(P1−P0)/P0.
In an embodiment, intended to measure leaks, the method comprises a step n), after step i, of measuring the pressure P11 in said first chamber 12, after a predetermined time t, with said valve 102 closed, the volume leak F being determined by the relationship:
F=Vo*(P1−P11)/(P0*t).
In embodiments, the method for calibrating a volumetric fluid handling system 2 comprising a plurality of n suction systems 10001-1000n, comprises successive steps (a′-m′) consisting of:
The internal volume Vok is determined by:
Vok=Vref*(P2k−Pck)/(P1k−P2k), wherein Pck=P00k+(P0yk−P00yk).
In embodiments, the method comprises a step n′) consisting in determining the calibrated displacement volume dV of the test suction system, calculated by dVk=Vok*(P1k−P0k)/P0k, and determining the calibrated displacement volumes dVi, wherein 1≤i≤n, of all the other suction system 10001-1000n. This is preferably done by using said first look-up table, the volumes dVi being determined by:
dVi=(Vok−Δi)*(P1i−P0i)/P0i.
In embodiments, wherein all main chambers 101-10n have the same volume the method comprises the steps (o′-q′) of:
As explained before, the pressure P1i is the pressure measured in the i-th main chamber 101-10n, wherein 1≤i≤n, when the volume change mechanism 1004 is in said proximal position Z1 and the valve 102 closed. The pressure P2i is the pressure measured in the i-th main chamber 101-10n, wherein 1≤i≤n, when the volume change mechanism 1004 is in the proximal position Z1 and the valve 102 opened.
In an embodiment, the method comprises a step r′ consisting of providing a second look-up table which contains the information of the liquid heights hi for different models of aspiration tips 1006 and for each defined liquid volume VL to be tested, and calculating a volumetric compensation Vci of the gravimetric effect, by taking into account said second look-up table, as described herein, by:
Vc=−h(a,b)*w*g*Vo/P0.
Said step r′ comprises also the calculation of the corrected displaced volumes VLi being determined by:
VLi=dV−Vci, wherein 0≤i≤n in the case of an embodiment of a system comprising a single test channel.
In an embodiment of a system 2 comprising a plurality of test channels C1-Cn, the volumetric compensation Vc of the gravimetric effect is determined by:
VLi=dVi−Vc, wherein 0≤i≤n.
In embodiments, in order to improve further the precision of the calibration process, the different steps of measuring the pressures in the main chambers and the reference chamber may be repeated so that mean values may be obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 24172380 | Apr 2024 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3962916 | Bouchy | Jun 1976 | A |
| 8561459 | Caldwell et al. | Oct 2013 | B2 |
| 20100286932 | Caldwell | Nov 2010 | A1 |
| 20120240663 | Feldmann | Sep 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 3608640 | Feb 2020 | EP |
| S61232833 | Oct 1986 | JP |
| Entry |
|---|
| D Bonzon et al., “Micropipette calibration by differential pressure measurements”, Measurement Science and Technology, vol. 30, No. 10, Aug. 8, 2019, 10 pages. |
| Webpage: Brandtech, Pipette leak testing units PLT unit, printed Dec. 31, 2024, 4 pages, at URL: https://www.brandtech.com/product/plt-pipette-leak-testing-unit/. |
| Webpage: AND, AD-1690 Leak Tester, printed Dec. 31, 2024, 2 pages, at URL: https://www.aandd.jp/products/test_measuring/pipette/ad1690.html. |
| Extended European Search Report for EP24172380.8, dated Oct. 16, 2024, 5 pages. |
