Flow-Mode Electrophoretic Mobility Measurement Apparatus
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Solution Overview
Problem
Conventional methods for measuring electrophoretic mobility of particles in solutions are limited by bulk fluid flow, which can overwhelm mobility measurements and lead to inaccurate results, especially when dealing with multiple species or small particles, and are prone to errors due to thermal convection and redox reactions.
Innovation Solution
The development of a flow-mode measurement apparatus that accounts for and subtracts out the effects of fluid flow velocity, using multiple detectors to minimize phase unwrapping errors and extend the upper limit of usable flow rates, and incorporates a leak-proof sample cell design capable of withstanding significant fluid pressure to prevent gas bubble interference and maintain sample integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If batch mode measurement is used, then measurement simplicity is maintained, but measurement precision deteriorates due to inability to account for fluid flow effects
Solution Approach 1:
The system transitions from static batch mode to dynamic flow mode, where sample continuously flows through the measurement cell. The flow rate is controlled and can be adjusted to optimize measurements while maintaining precision. The system dynamically accounts for flow velocity effects through mathematical correction.
Solution Approach 2:
The system incorporates feedback mechanisms where the measured velocity data is used to calculate and subtract the flow contribution. The corrected electrophoretic mobility is then obtained by removing the flow-induced velocity component from the total measured velocity.
2Productivity
If higher flow rates are used, then productivity is improved through faster sample analysis, but measurement precision deteriorates due to flow overwhelming electrophoretic signal
Solution Approach 1:
The system extracts the flow velocity contribution from the total measured velocity signal. By separately measuring or calculating the flow rate and its effect on particle velocity, this flow component is removed to isolate the pure electrophoretic mobility signal, enabling accurate measurements even at higher flow rates.
Solution Approach 2:
The system changes the measurement parameters by operating in flow mode rather than batch mode. The flow rate itself becomes a controllable parameter that can be optimized - high enough to provide good mixing and heat dissipation but low enough to maintain measurement accuracy through mathematical correction.
3Temperature
If conventional batch mode is used, then device complexity is minimized, but heat dissipation efficiency deteriorates leading to thermal convection errors
Solution Approach 1:
The continuous flow of sample through the measurement cell provides ongoing heat dissipation. Rather than heating up in a closed batch system, the flowing sample continuously carries away heat, preventing thermal convection currents that would interfere with electrophoretic measurements.
4Measurement precision
If multiple detectors are added, then measurement precision is improved by reducing phase unwrapping errors, but device complexity increases
Solution Approach 1:
The measurement function is segmented across multiple detectors positioned at different locations or angles. Each detector captures a portion of the phase information, and the combined data from all detectors provides complete phase information without unwrapping errors, improving measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, real-time, online measurement of electrophoretic mobility with improved resolution for multiple species, reduced impact from thermal convection and redox reactions, and efficient heat dissipation, allowing for higher flow rates and more robust characterization of samples, including those with high salt concentrations.
Implementation Method 1
Electrophoresis is the migration of macro-ions under the influence of an electric field. A steady-state electrophoretic velocity, ve, attained by the migrating macro-ions is linearly proportional to the applied electric field.
Implementation Method 2
The electrophoretic mobility can also be measured by an electroacoustic means: electrokinetic sonic amplitude, ESA, as described by Oja, et. al. in U.S. Pat. No. 4,497,208, Issued Feb. 5, 1985, 'Measurement of Electro-Kinetic Properties of a Solution.'
Implementation Method 3
In general, the movement of macromolecules can be diffusional, due to Brownian motion, and collective, due to electro-osmosis, electrophoresis, externally applied fluid flow, thermal convection, etc. In order to determine the electrophoretic component, the contributions to molecular motions from other mechanisms must be accounted for. The contribution from random Brownian motion is necessarily averaged out over multiple measurements.
Implementation Method 4
The effects of electro-osmosis can be ignored by measuring at the stationary layer, or by increasing the frequency of electric field reversal to suppress electro-osmosis.
Implementation Method 5
The contribution from thermal convection or residual bulk fluid flow can be subtracted out since it is independent of the direction of the applied electric field and shows up as a constant velocity component while the electrophoretic component switches polarity in synchronicity with the alternating electric field.
Data Source
AI summary
When measuring electrophoretic mobility it is customary to apply an electric field and determine the electrophoretic velocity while minimizing all other contributions to the particle movement. A method and apparatus for the measurement of mobility while the sample is flowing is disclosed. Combined with a fractionation system, this approach further enables the direct measurement of individual species' mobility within a multi-modal sample. Other advantages of this new mobility measurement approach include the ability to easily pressurize the sample to suppress electrolysis, mitigation of oxidation-reduction effects and efficient heat dissipation.