[LookAroundYou]

Hi all,

I am trying to isolate a compound that at pH 0.27 has a charge of +1. The compound I am trying to separate it from is neutral at that pH. Both compounds have similar partitian coefficients (about 3.00) and masses (about 300g/mol). I was wondering if it might be possible to use this positive charge to separate it from my other compound by placing electrodes in my solution.

So far, I imagine I would set the experiment up as follows:

I have Compound A and B along with other impurities in a EtOH/Water solution. The Ethanol to water is approximately 90%:10% by volume respectively. I would adjust pH to ~0.27 by adding 0.6 mol of HCL per liter of solution. I would place an anode on one end and a cathode on the opposite end. I would let some time elapse (idk maybe 30 min) and then place an impermeable physical separator in the middle of the solution between the electrodes. At this point, I would hope that the positively charged compound has made its way to the anode and I would drain the side with the cathode and assume it would be free of any positively charged molecules.

Does this seem viable? What are some considerations I should make? Any obvious flaws I may have missed?

Thanks in advance for constructive criticism and thoughtful answers.

[LookAroundYou]

Also, I do not want to use a gel matrix because there is no need for a perfect isolation of the positively charged compound. I simply want to be able to have a solution containing everything but the charged compound. Waste is not a large concern but throughput is.

Thanks again all!

[Borek]

I was wondering if it might be possible to use this positive charge to separate it from my other compound by placing electrodes in my solution.

Won't work, unless you use insane voltages. Besides, at that low pH you have plenty of other ions that will migrate much faster. Once they are close to the electrode they will create an electric field effectively canceling the external electric field, so the ions inside won't migrate any further.

However, can't you remove the neutral compound by extraction with some immiscible solvent?

[rolnor]

There is a separation tecnique called electrophoresis that is close to what you want to do, this is used for analysis, not preparative separation.

[LookAroundYou]

I am familiar with electrophoresis for use on biomolecules and proteins for separation and analysis. There is a technique called preparative electrophoresis that I just learned about but this has better resolution than I need and uses a gel to help provide this resolution. I don't want to use gel if I don't need to.

In the presence of water, the HCl dissociates to become H+ and Cl-. My thought was that these ions, in the presence of electrodes, would simply move toward their respective oppositely charged electrode. How do they form electric fields? How does this concept work with electrophoresis and not in my "simpler" concept?   

I haven't been able to find a imiscible solvent system that will crystallize the charged compound yet. Any advice for this approach?

Thanks again everyone!

[Borek]

In the presence of water, the HCl dissociates to become H+ and Cl-. My thought was that these ions, in the presence of electrodes, would simply move toward their respective oppositely charged electrode. How do they form electric fields?

You have an excess of positive charges on one side, and and excess of positive charges on another side. That means there is an electric field and potential difference between them, not much different from what happens in the capacitor. Physics 101.

How does this concept work with electrophoresis and not in my "simpler" concept?

Electrophoresis faces exactly the same problems. High voltages help.

I haven't been able to find a imiscible solvent system that will crystallize the charged compound yet. Any advice for this approach?

I am suggesting quite the opposite - removing the neutral compound. I guess what you are really interested in is purification of the charged one, if you can't separate the charged one, perhaps removing other ones will help?

[LookAroundYou]

The charged compound is in a concentration of about 100 ppm. So only a small amount needs to be attracted to the negatively charged electrode. Does this make much of a difference?

Why does electrophoresis work and my set up seem like it won't? Sorry, I am not quite understanding what is different except for the absence of the aragose gel matrix (which from my understanding only serves to separate different charged particles from each other based on their size).

Thanks for helping me understand what I am missing? Also, what voltages would be required to be successful?

[Borek]

The charged compound is in a concentration of about 100 ppm. So only a small amount needs to be attracted to the negatively charged electrode. Does this make much of a difference?

Perhaps. No idea to be honest.

Why does electrophoresis work and my set up seem like it won't? Sorry, I am not quite understanding what is different except for the absence of the aragose gel matrix (which from my understanding only serves to separate different charged particles from each other based on their size).

Electrophoresis uses voltages in the hundred V range and the gel is there to to prevent convective mixing and to slow down the diffusion. The ions we typically work with in the electrophoresis are quite large, so their diffusion is slow and migration is much more important. Then, we put the sample to be analyzed into a spot, it doesn't occupy whole volume.