Method to measure electrophoretic mobility of a flowing sample
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.
1. A method comprising:
flowing a sample solution comprising particles through a sample cell comprising
a measurement chamber configured to allow the sample solution to flow in a direction essentially parallel to a path of a laser beam transmitted through the measurement chamber,
a fluid inlet coupled to the measurement chamber and configured to introduce the sample solution into the measurement chamber, and
a fluid outlet coupled to the measurement chamber and configured to allow the sample solution to exit the measurement chamber; and
generating, via electrodes, an alternating electric field across the measurement chamber and essentially perpendicular to the direction;
fractionating the sample solution; and
measuring a concentration of each species in the sample solution, resulting in a measured concentration of the each species in the sample solution.
2. The method of claim 1 wherein the fractionating comprises fractionating the sample solution via a field flow fractionation system.
3. The method of claim 1 wherein the fractionating comprises fractionating the sample solution via a size exclusion chromatography system.
4. The method of claim 1 wherein the measuring comprises measuring the concentration via a refractive index detector.
5. The method of claim 1 further comprising measuring a hydrodynamic radius of the each species in the sample solution, resulting in a measured hydrodynamic radius of the each species in the sample solution.
6. The method of claim 5 further comprising calculating a molecular charge of the each species in the sample solution with respect to the measured concentration and the measured hydrodynamic radius.