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Combining Step Gradients and Linear Gradients in Density
journal contribution
posted on 2015-06-16, 00:00 authored by Ashok
A. Kumar, Jenna A. Walz, Mathieu Gonidec, Charles R. Mace, George M. WhitesidesCombining aqueous multiphase systems
(AMPS) and magnetic levitation
(MagLev) provides a method to produce hybrid gradients in apparent
density. AMPSsolutions of different polymers, salts, or surfactants
that spontaneously separate into immiscible but predominantly aqueous
phasesoffer thermodynamically stable steps in density that
can be tuned by the concentration of solutes. MagLevthe levitation
of diamagnetic objects in a paramagnetic fluid within a magnetic field
gradientcan be arranged to provide a near-linear gradient
in effective density where the height of a levitating object above
the surface of the magnet corresponds to its density; the strength
of the gradient in effective density can be tuned by the choice of
paramagnetic salt and its concentrations and by the strength and gradient
in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic
field gradient, enables their use as media for MagLev. The potential
to create large steps in density with AMPS allows separations of objects
across a range of densities. The gradients produced by MagLev provide
resolution over a continuous range of densities. By combining these
approaches, mixtures of objects with large differences in density
can be separated and analyzed simultaneously. Using MagLev to add
an effective gradient in density also enables tuning the range of
densities captured at an interface of an AMPS by simply changing the
position of the container in the magnetic field. Further, by creating
AMPS in which phases have different concentrations of paramagnetic
ions, the phases can provide different resolutions in density. These
results suggest that combining steps in density with gradients in density can enable new classes of separations
based on density.