SINGLE OPERATION MICROPIPETTE CALIBRATION MECHANISM
FIELD OF INVENTION
The present invention relates to a micropipette/pipettor/pipette that is a measuring device that is used to transfer (aspirate and dispense/discharge) an adjustable micro-volume of liquid down to 0.1µl, and more particularly to a single operation calibration mechanism of the dispense volume of a micropipette which eliminates the complexity present in other calibration procedures therefor.
BACKGROUND ART
A micropipette is a device that is used in conjunction with a tip to transfer an adjustable volume of liquid (usually in micro-litres) from one location to another precisely (as governed by ISO 8655-2:2002), in the process of sample preparation for experiments in a laboratory. Manually-operated air-displacement micropipettes, which are most relevant with respect to this application, operate by creating a vacuum via the retraction of a piston located in the micropipette body. Thus, when the open end of an associated pipette tip is immersed in a liquid, the resulting vacuum draws air from the micropipette tip and an equivalent amount of the liquid is consequently drawn into the tip to replace the evacuated air. Movement of the pipette piston is regulated and adjustable in a variable volume micropipette such that a desired amount of liquid is drawn precisely into the tip during the aspiration phase of the pipetting operation. One the liquid is aspirated, the piston can then be pressed to dispense all the liquid in the tip, so that the quantity of liquid is transferred from one location to another during the Dispense Phase of pipetting.
A common drawback to known micropipettes is the method of calibration of the same when the micropipette is out of calibration or is aspirating/ dispensing a volume of the liquid which is different from the desired quantity of liquid beyond the acceptable error limits (as defined by ISO 8655-2 : 2002). For instance, a micropipette with a nominal volume (capacity) of 1000ul is allowed to have a +/-60ul of systematic error and +/- 30ul of random error. If the micropipette exhibits more than the permissible error, it is considered to be out of calibration. In such cases, the micropipette is required to be re-calibrated.
DRAWBACK
Using current methods of micropipette re-calibration, extensive time and effort is required to re-calibrate—particularly when the difference between the current volume setting and a desired volume setting is large (as measured by dispensing liquid into a container being weighed by an analytical balance). For example, in the case of known micropipettes:
a) Most calibration procedures rely on hit-and-trial methods and matching markers on a pipette to a chart in a instructional manual, which are time consuming and frustrating
b) Some calibration procedures require disassembly of certain pipette components which make the procedure complex and time-consuming
c) The time consuming and complex nature of current pipette calibration mechanisms forces users to send pipettes for expensive and time-consuming re-calibration at third-party facilities even for minor adjustments.
CURRENT CALIBRATION PROCEDURES
All calibration procedures require the determination of an average weighted dispense volume (at a particular set/desired volume) by dispensing multiple samples into a container measured by an analytical balance. After the average weighted volume is determined, one of the following methods are used for recalibration.
1) Method 1: Matching Revolutions/Markers to Adjustment Chart in the Manual
This mechanism requires the user to use a calibration tool provided with the micropipette to adjust the calibration of the pipette using a hit-and-trial method. After the average weighted dispense volume of the pipette is determined, the technician is supposed to adjust the calibration nut using the calibration tool according to a scale marking on the pipette body. The scale on the pipette has to be matched to a chart (usually provided in the user manual) to figure out the actual volume adjustment made on the pipette. Examples of such a calibration systems can be found in pipettes manufactured by the following manufacturers:
a) Eppendorf :
https://www.eppendorf.com/IN-en/service-support/knowledge-base/literature/manuals/
See Research Plus, Factory Adjustment Page 8-12
b) Nichryo: Video explanation of Calibration Procedurehttps://www.youtube.com/watch?v=poNJah9xzlo
Disadvantage : Since the scale has a LOW resolution and the markings on the scale have to be matched visually (not accurate), this mechanism requires the user to repeat the process of adjusting the calibration nut multiple times (hit-and-trial) until the desired volume is being dispensed consistently. This process is in-efficient and therefore, time consuming.
2) Method 2: Calibration by disassembling and disengaging the digits from the plunger mechanism
This method can be found in pipettes manufactured by Brand Gmbh and Socorex - After the average weighted dispense volume is determined, this mechanism requires the user to disassemble the grippy of the micropipette AND disengage the digits from the plunger mechanism. The average weighted dispensed volume can then be set on the digital mechanism (digits) by rotating the plunger without changing the dispense volume of the micropipette. The digits then need to be re-engaged to the plunger mechanism and the component shave to be re-assembled. If the pipette is still not calibrated, the disassembly procedure has to be repeated. Even though this is NOT a hit-and-trial method, the requirement for disassembly and reassembly of micropipette components makes the procedure complex and time-consuming.
Documentation: -
a) Socorex
https://www.socorex.com/images/Documents/LAB/Operating%20Instructions/Acura%20manual/Socorex_Acura_manual_815_825_835_855_Operating_Instructions_EN_DE_FR.pdf
See Section CALIBRATION on Page 7
b) Brand Gmbh
https://shop.brand.de/media/import/1/27/32406/42485/42649/49381/Transferpette_S_2020_EN.pdf
See Section Easy Calibration Technology on Page 11
As would also be understood by one of skill in the art, calibration of the dispensed fluid volume is essential for consistently accurate pipetting. Consequently, micropipettes are typically calibrated at the factory and may also be calibrated during servicing operations but the current calibration procedures are complex to understand and time-consuming to execute for both laboratory users and service technicians.
SUMMARY OF INVENTION
Accordingly, a manually operated variable volume micropipette according to the invention addresses the shortcomings of calibration procedures in presently commercially available handheld micropipettes, and introduces a single operation calibration functionality not possible in traditional manual pipettes.
One embodiment of a manual micropipette according to the present invention is a time-efficient and user-friendly procedure for scientists and technicians to calibrate micropipettes precisely in a laboratory to enable quick and effortless re-calibration. This Single Operation Calibration mechanism for Micropipettes enables User Calibration and Factory Calibration in a Single Operation WITHOUT disassembling any component of the micropipette OR disengaging of the digital system (digits) from the plunger OR matching of calibration markers/revolutions on a pipette to volume adjustment charts in a user instructional manual. It eliminates the complexity from various micropipette calibration procedures.
In an exemplary embodiment the said manual micropipette according to the present invention comprises a calibration tool that can simultaneously couple the plunger with the calibration nut which is not possible in traditional micropipettes. In case that the pipette is out of calibration, the calibration tool enables the user to adjust the digital system (digits) of the micropipette to the average weighted dispense volume without altering the vertical distance between the plunger and the calibration nut (See Fig. 4). The set/desired volume on the pipette is modified while the dispense volume remains at the average weighted volume quantity. Since both are synchronized in a single operation, the pipette is recalibrated without any complexity of hit-and-trial methods and assembly/disassembly methods.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates the plunger and calibration nut in accordance with the present invention;
Fig. 2 illustrates the calibration tool in accordance with the present invention;
Fig. 3 illustrates how the calibration tool engages both the plunger and calibration nut in accordance with the present invention;
Fig. 4 illustrates the internal components of pipette and calibration mechanism in accordance with the present invention;
Fig 5 illustrates a chart depicting the resultant differences in the readings calculated before & after calibration in accordance with the present invention;
Fig 6 illustrates the calibration report issued by sample laboratory generated calibration certificate.
DETAILED DESCRIPTION
Referring initially to FIG. 1, an overview illustration of a manual-micropipette according to the invention is presented. In general configuration, the micropipette is similar to a traditional micropipette with a plunger and a guide tube, in that a user grips a handheld body of the pipette and manipulates a spring-loaded plunger button to control the intake and discharge of fluids through a disposable tip, which is coupled to the end of the micropipette. The micropipette includes a plunger shaft upon which the plunger button is mounted. The rotation of the plunger button serves as the volume-setting mechanism or adjusting the desired volume from the pipette.
The herein disclosed micropipette is fitted with an unique calibration tool (Fig. 2) that can engage both the plunger and the calibration nut with the micropipette (Fig. 3.). No other pipette offers such a threaded calibration tool. With the use of the calibration tool, the user is able to rotate the calibration nut in conjunction with the plunger button. Since the pitch of the threaded part of the plunger and the threads of the calibration nut are the same, it allows the same vertical movement of both the plunger and the calibration nut during use of the calibration tool. This maintains the vertical distance between the plunger button and the calibration nut AND adjusts the digits (by the rotating plunger) to the desired observed volume.
Component Details:
Plunger: Found below the plunger ring, the plunger has 2 major functions:
a) Aspirate and dispense the liquid in the micropipette tip - The plunger has two steps/stages. For aspiration, the plunger is pressed to the first stage and released. For dispensing, the plunger is pressed to the first stage and then pressed to the second stage to release any remaining liquid from the tip. This ensures accuracy of a micropipette.
b) Driving the Digital System - The rotation mechanism of the plunger drives the display measuring meter, which helps adjust both the displayed volume on the micropipette device and the corresponding vertical plunger/piston movement.
Calibration Nut: The calibration nut defines the bottom point during the movement of the plunger. The position of the nut can be adjusted with the help of a calibration tool for slight adjustments during the calibration process. This increases or decreases the vertical movement (depending on the rotation of the tool) of the plunger and hence the aspirated/dispensed volume.
Microlit Calibration tool: It helps in configuring the micropipette to get desired accuracy and precision. The tool engages the plunger, calibration nut, and the digits of the pipette and can be used to configure the pipette without disassembling any components or disengaging the digits.
Threaded part: The threaded part allows the vertical movement of the plunger upon rotation. This vertical movement adjusts the set volume of the micropipette.
Display System: The display system displays the current set volume of the micropipette. It can be adjusted by rotating the plunger.
Ejector button: The press of the ejector button allows the removal of the tip (attachment) from the micropipette without touching the tip. This prevents any possible contamination
If the performance results of the micropipette are no longer within the recommended values (as defined by ISO 8655:2-2002) or if changes occur in physical parameters (liquid density, temperature), recalibration can be performed using the Microlit Calibration Tool by following the procedure:
1) Perform at least 5 measurements on the nominal volume of the pipette and calculate the average weighted dispense volume as measured by an analytical balance
2) Engage the Microlit Calibration Tool with the plunger and the calibration nut and adjust the digits to display the average weighted dispense volume. Once the average weighted volume is displayed, the pipette has been recalibrated. It is that simple!
3) Perform a few plunger operations to check the resulting volume
This mechanism works by adjusting the digit mechanism of the pipette to the average weighted volume of the readings and keeping the vertical movement distance between the plunger and the calibration nut exactly the same (and so the aspirated/dispensed volume). This is achieved by making the pitch of the threads of the calibration nut and threaded part of the plunger the same (Fig4) – not true in current pipettes in the market. As illustrated above, this procedure does not require any hit-and-trial method or any disassembling of pipette components or matching calibration markers/revolutions with charts in a user manual.
The invention proposes a unique calibration tool ( Fig. 2 ) that can engage both the plunger and the calibration nut with the micropipette. (Fig. 3). No other pipette manufacturer’s offers such a tool.
EXPERIMENTS
The experimental data belowpresents the evidence for the invention.
An uncalibrated Single Channel Variable Volume Pipette 100-1000ul was taken for this purpose.
To calibrate the pipette, we performed measurements of the dispensed volume on an analytical balance and took an arithmetic mean of the readings and multiplied it with the Z factor (1.0026) to convert from the weight observed on the balance to the dispensed volume. The value obtained 989.5ul is the average weighted volume before calibration.
The obtained average weighted volume989.5ul was set on the digital system (digits) using the Microlit Calibration Tool in a Single Operation. Theoretically, this should have re-calibrated the pipette.
To test the calibration, 5 more readings were taken at the nominal volume (1000ul). The results are recorded in the table below.

Table 1 -Illustrating the measurements performed before and after calibrating the pipette using the single operation method.
S. No. Before Calibration After Calibration
1 Performed five measurements: 985.2 µl, 985.8 µl, 986.0 µl, 988.8 µl, 988.9 µl. Performed five measurements: 998.8 µl, 999.1 µl, 998.7 µl, 999.8 µl, 999.5 µl.
2 The average weighted volume (986.94 µl) * Z-factor (1.0026 mm3/mg) = 989.50 µl. The average weighted volume (999.18 µl) * Z-factor (1.0026 mm3/mg) = 1001.7 µl
3 Status: Un-calibrated Status: Calibrated
*As per ISO-8655, the permissible limit for accuracy of the 1000 µl micropipette should +/- 0.6%( between 994 µl to 1006 µl)

*This has to be noted that all the measurements were taken on the analytical balance under the suitable laboratory environments.
We can observe from the data above that the micropipette was calibrated in a simple single operation using the Microlit Calibration tool.
As shown in Fig 5, the Brown line depicts that the data is accurate and is under calibrated volume (as per ISO norms). NO Hit-And-Trial methods were used for the calibration of the pipette.
The Fig 6 includes a sample laboratory generated calibration certificate which will accompany the calibrated pipette.

ADVANTAGES
1) Single Operation Calibration - No hit-and-trial
2) No disassembly of micropipette components
3) No disengaging of plunger from the digital system mechanism
4) No requirement to use a table/chart to match calibration markers on pipette to compute adjusted volume
Many modifications may readily be contemplated by those skilled in the art to which the invention relates. Many further modifications may readily be contemplated. The description set out above is particularly applicable to high rate clarification applications. However, in conventional clarification where the upstream or downstream processes herein described are not used, the teachings according to the invention may have considerable merit and are also applicable. The specific embodiments described, therefore, should be taken as illustrative of the invention only and not as limiting its scope as defined herein.
,CLAIMS:We Claim:
1. A micropipette with single operation calibration mechanism comprising of :-
- a guide tube;
- a plunger including a plunger shaft, ring with threaded portion and plunger button inserted in the guide tube in a sliding manner;
- a chamber (micropipette tip) for accommodating a liquid to be dosed being aspirated or dispensed according to a movement of a plunger;
- a digital meter drive system operably connected with the rotation mechanism of the plunger which drives the display measuring meter,
- a calibration nut defining a bottom point during the movement of the said plunger;
a calibration tool operably connected with the said plunger, calibration nut, and the digits of the digital meter wherein
the pitch of the said threaded portion and the calibration nut are the same which allows same and simultaneous vertical movement of the plunger and the calibration nut during the operation of the calibration tool.
2. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the said plunger ring functions during aspiration and dispensing in two stages.
3. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the said display measuring meter is configured to adjust both the displayed volume on the micropipette device and the corresponding vertical plunger/piston movement.
4. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the position of the said calibration nut is adjustable with calibration tool for slight adjustments during the calibration process.
5. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the operation of the calibration tool over the calibration nut increases or decreases the vertical movement (depending on the rotation of the tool) of the plunger and correspondingly the aspirated/dispensed volume.
6. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein said calibration tool engages the plunger, calibration nut, and the digits of the pipette and can be used to configure the pipette without disassembling any components or disengaging the digits
7. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the said threaded part allows the vertical movement of the plunger upon rotation and thereby adjusts the set volume of the micropipette
8. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the said display system displays the current set volume of the micropipette which can be adjusted by rotating the plunger.
9. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein the said micropipette includes an ejector button which allows the removal of the tip (attachment) from the micropipette without touching the tip and elimination any possible contamination.
10. The micropipette with single operation calibration mechanism as claimed in claim 1, wherein said micropipette includes a plunger shaft upon which the plunger button is mounted; and
wherein the rotation of the said plunger button serves as the volume-setting mechanism or adjusting the required volume from the pipette.