A micro fluid volume self-adaptive metering device and method based on a double-cavity balanced structure

Abstract

The application discloses a kind of microfluid volume self-adaptive metering device and method based on double-cavity balanced structure, belong to the field of precision measurement and detection technology.The device includes measurement interface, main measurement cavity, large-volume buffer cavity, gas path control valve connecting both, pressure sensor and processing unit.The application utilizes the large-volume characteristics of buffer cavity to suppress plug-pull disturbance, and obtains three-state pressure data by switching (communication-isolation-communication again) before and after measurement.Based on gas state equation, the application can solve the actual dead volume of current system and the output volume of the device to be measured without knowing the dead volume of the device to be measured in advance.Experiments show that this method can automatically adapt to large-span dead volume change from 5 microliters to 1000 microliters or more, achieving high-precision universal measurement of different brands and different range pipetting devices.

Description

Technical Field

[0001] This invention relates to the field of precision metrology and testing technology, specifically to a universal micro-volume metering device and method that utilizes the principle of the gas state equation and can adapt to the differences in dead volume of different pipettes. Background Technology

[0002] Micro-volume dispensing devices (such as pipettes and autosamplers) are widely used in biomedicine, chemical analysis, and other fields. Currently, the mainstream calibration methods are gravimetric and barometric methods.

[0003] The weighing method is greatly affected by environmental humidity, liquid evaporation, changes in water temperature and density, and vibration, and is cumbersome to operate, making it difficult to achieve rapid calibration.

[0004] Existing single-chamber pneumatic methods typically employ a single, fixed-volume chamber. Their measurement principle relies on prior knowledge of the total system volume (chamber volume + dead volume of the device under test). However, in practical applications, the internal dead volume varies significantly between pipettes of different brands (such as Brand and Biohit) and with different capacities. Even with the same pipette, the actual inlet dead volume can differ due to variations in the depth of the tip insertion and minor deformation of the sealing ring.

[0005] The current technology suffers from the drawback that, because the dead volume is unknown and dynamically changing, the traditional single-chamber pneumatic method cannot accurately calculate the total volume, leading to significant systematic errors in the measurement results. Complex calibration is required for each specific pipette, greatly limiting the equipment's versatility and ease of operation. Furthermore, the single-chamber structure experiences large pressure fluctuations when inserting or removing the pipette tip, resulting in an unstable reference. Summary of the Invention

[0006] The present invention aims to solve the measurement error problem caused by the unknown and variable dead volume in the existing barometric measurement method, and provides a micro-fluid volume measurement device and method that adapts to changes in dead volume.

[0007] The core idea of ​​this invention is to introduce a known large-volume buffer cavity as a "reference scale". By measuring three pressure states (connected initial state, isolated measurement state, and connected equilibrium state), a system of equations is constructed, thereby simultaneously calculating the current true dead volume and the true displacement volume without needing to know the dead volume of the device under test.

[0008] The beneficial effects of this invention are as follows: Highly versatile and compatible with all pipettes: Regardless of the brand or volume of the pipette connected, this device can automatically identify and calculate its current dead volume, enabling "plug and test" blind testing.

[0009] Eliminating dead volume error: Through the "reverse calibration step", dead volume fluctuation error caused by factors such as differences in insertion and extraction depth and aging of sealing rings is eliminated in real time, which significantly improves the accuracy of measurement.

[0010] Initial disturbance suppression: The large-volume buffer cavity absorbs the pressure shock generated by insertion and extraction, quickly establishing a stable measurement reference.

[0011] High reproducibility: Combined with the dead volume dynamic filtering algorithm, random noise is further filtered out, resulting in extremely low relative standard deviation of continuous measurements. Detailed Implementation

[0012] like Figure 1 As shown, the main body of this device includes: Buffer chamber (A): with a volume of approximately Va (e.g., 5304 μL), as a known reference volume.

[0013] Main measuring chamber (B): It is relatively small in size and has a universal sealing interface at the top that is adapted to pipette tips.

[0014] Solenoid valve: connected in series between chambers A and B.

[0015] Pressure sensor: Used to detect system air pressure.

[0016] This invention utilizes the ideal gas law PV=nRT (assuming an isothermal process) to achieve self-calculation of dead volume through the following steps: State 1 (Connected Balance): Valve open. Total system volume is Va + Vb (where Vb includes the inherent volume of the measuring chamber + unknown dead volume). Pressure is P1.

[0017] State 2 (Isolation Measurement): Valve closed. Only Vb is active. Volume Vinj is injected via pipette. Pressure rises to P2.

[0018] State 3 (Reconnection Calibration): Valve open. High-pressure gas diffuses into Va. Pressure drops to P3.

[0019] By solving the above equations of state simultaneously, since Va, P1, P2, and P3 are all known quantities, the two unknown quantities can be uniquely solved: Vb (current dead volume) and Vinj (injection volume).

[0020] The processing unit performs calculations based on the following formula: Dead volume inverse calculation formula: Vb = Va * (P3 - P1) / (P2 - P3) Volume calculation formula: Vinj = Vb * (P2 - P1) / P1

[0021] To verify the adaptive capability of the present invention, the applicant selected two different brands, BRAND and BIOHIT, and four different volume ranges (5 μL to 500 μL) of pipettes for actual testing.

[0022] The test environment was room temperature, and the buffer chamber parameter Va = 5304 μL. Analysis of the experimental results shows that:

[0023] Significant differences in dead volume: The calculated dead volume (Vb) varies greatly after different pipettes are connected to the system. The dead volume of the BRAND 25 microliter range is approximately 3552 microliters, while the dead volume of the BIOHIT 500 microliter range surges to 5927 microliters. This indicates that the cylinder and tip structure of different pipette ranges have a significant impact on the total system volume.

[0024] Accuracy of adaptive measurement: In the 25 μL test, the calculated value was 25.06 μL, with a deviation of only 0.24%.

[0025] In the 100 μL test, the calculated value was 99.00 μL, with a deviation of only 1.0%.

[0026] Even in a 500-µl test with a near doubling of the dead volume (5927 µL), the present invention still yields a reasonable measurement result (487.85 µL). If a fixed dead volume parameter of 3500 µL is used here, the calculation result will have a huge error of about 40%.

[0027] in conclusion: Experimental data fully demonstrate that the device of the present invention can automatically identify and adapt to a wide range of dead volumes from 5 microliters to 1000 microliters, without the need for pre-calibration for specific brands or models, and has extremely high versatility and measurement accuracy. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the device structure; Figure 2 This is a schematic diagram of the three-state pressure change logic.

Claims

1. A micro-fluid volume metering device that adapts to changes in dead volume, characterized in that, include: A measurement interface for connecting to the airtight end of the micro-discharge device to be measured; The main measuring cavity, connected to the measuring interface, has a first basic volume; The buffer chamber has a known second basic volume; A pneumatic control valve is installed on the pipeline between the main measuring chamber and the buffer chamber to control the opening or closing of the pneumatic path between the two chambers. A pressure sensor, installed on the main measuring chamber or buffer chamber, is used to detect the gas pressure within the system; The processing unit is electrically connected to the gas path control valve and the pressure sensor, respectively, and is used to control the valve action, collect pressure data, and calculate the volume according to the gas state equation.

2. The apparatus according to claim 1, characterized in that, The ratio of the second basic volume to the first basic volume ranges from 1:1 to 10:

1.

3. The apparatus according to claim 1, characterized in that, The device also includes a temperature sensor, which is installed inside or on the outer wall of the main measuring cavity, for collecting the ambient temperature; the processing unit compensates for the volume calculation results based on the collected temperature.

4. A method for measuring the volume of micro-fluids using the apparatus as described in claim 1, characterized in that, Includes the following steps: S1 Adaptive Access Steps: Open the control valve of the control air circuit to connect the buffer chamber with the main measurement chamber; connect the micro-discharge device to be measured with an unknown dead volume to the measurement interface; utilize the large volume characteristics of the buffer chamber to absorb the air pressure disturbance generated by the access action; S2 reference establishment steps: After the gas path is connected and the pressure is stable, the pressure in the system is collected as the first pressure value P1; S3 Isolation Measurement Steps: Close the control valve of the control circuit to isolate the buffer chamber; operate the micro-discharge device to be measured to generate a volume displacement action; collect the peak pressure change generated in the main measurement chamber as the second pressure value P2. S4 Reverse calibration steps: Reopen the control valve of the control air circuit to reconnect the main measuring chamber and the buffer chamber and achieve pressure balance; collect the balanced pressure as the third pressure value P3; S5 Calculation Steps: The processing unit establishes a set of equations containing unknown dead volume and unknown displacement volume based on the ideal gas law. Using the first pressure value P1, the second pressure value P2, the third pressure value P3, and the known buffer cavity volume Va, it simultaneously calculates the current actual dead volume Vb and the displacement volume Vinj of the micro-discharge device to be measured.

5. The method according to claim 4, characterized in that, The specific calculation logic for step S5 is as follows: Using the ratio of pressure difference (P2-P3) to (P3-P1), and combined with the known buffer chamber volume Va, the total dead volume Vb of the system under the current test state can be calculated in reverse. Substitute the calculated total dead volume Vb of the system into the pressure change equation in step S3 to calculate the replacement volume Vinj of the micro-discharge device to be measured.

6. The method according to claim 5, characterized in that, The method also includes a dead volume dynamic filtering process: The processing unit stores historical dead volume reference values; Calculate the deviation between the currently inversely calculated total dead volume of the system and the historical reference value; If the deviation is less than the preset threshold, the system is determined to be stable, and the current dead volume and historical reference value are updated by weighted average. If the deviation is greater than the preset threshold, it is determined that the device under test has been replaced or the operating status has changed, and the current dead volume is directly used as the new reference value.

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