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Washington State University
The Gene and Linda Voiland School of Chemical Engineering and Bioengineering

Saltwater ITP Experiment

The experiment below was run in response to a reviewer’s comment that ITP would not work with seawater. The column was first filled from the bottom to a middle port with leading electrolyte (TrisHCl @ pH 10.5) and then filled from the middle feed port to the top with terminating buffer (EACA @ pH 10). A sample of model seawater containing 400 mM NaCl among other salts plus bromomethyl blue and methyl red (as model target ions) was then injected into the column through the middle feed port. Power was applied at 4 kV to begin ITP and a small back flow was applied from the bottom of the column to drive the ITP train to a fixed, steady-state position.

Although the presence of so much salt slows the evolution of the ITP train, i.e., it takes more than an hour at this scale, it is clear that the two dyes have formed tight, concentrated bands after the sodium and chloride ions have migrated out of the instrument at the cathode and anode respectively. Double-click on the movie to restart it. They are not optimized for streaming so be patient as it may take more than a full minute to load the movies if you are on a T10 connection. Call me at (509) 335-7716 for more information.

Saltwater ITP Numerical Simulation

This movie Illustrates how sodium in a sample of seawater leaves an ITP channel if sodium migrates faster than the leading cation. Initially, the sample containing 400 mM sodium occupies about 1/5 of this channel. When power is turned on at 200 volts, the sodium (next movie) quickly moves to the front of the ITP train and then slowly exits the channel on the right. The target analytes, which are slower than the leader in this simulation, stack into high-concentration zones (bottom movie) at their steady-state positions just behind the backside of the sodium. Time is in seconds.

It takes just over 2 minutes for the target cations to reach their steady-state positions in the channel, after which the zones will remain stacked in that position. The parabolic distortion of the target bands is caused by electrokinetic counterflow (electroosmosis) through the concentrated cation zones.