Capillary Electrophoresis - What is the buffer for?

[Deoxyribonucleon]

In CE, both ends of the capillary tube are submerged in buffer solution. Is the purpose of the buffer solution to keep the pH above 4, so that the silica attached to the inner wall of the capillary tube remains ionised?

[acetone]

yes to make sinalol (pKa about 2.3) charged, need pH >4.3 or larger and then make the main fluid body move called electroosmotic flow(EOF).

[Deoxyribonucleon]

Ah right, that makes sense. Thanks.

[cari]

In CE (or any form of electrophoresis) you need charge on your compound in order to separate them. That means that you want to control the pH of your separation medium, so you control the charge of your compounds.
The capillary in CE is filled with your medium, but in order to apply the high voltage and make good contact with the electrodes, the easiest thing is to stick both your capillary end and your electrode in a vial with your medium.
Because you get electrolysis of water at the electrodes when the voltage is turned on, you get H+ and OH- formation in the respective vials. To make sure that your medium remains the pH you so carefully selected, you want to buffer the medium.
So that explains why the capillary ends are put in vials containing buffer.

But more happens if you fill a capillary with an (aqueous) medium: the silanol groups of the capillary wall might deprotonize. The higher the pH, the more this happens. As a consequence, an electric double layer will be formed, primarily form your buffer cations. If then the separation voltage is switched on, this results in an electro-osmotic flow towards the cathode. More details about this mechanism you can soon read in a new series of CE articles to be published on SepScience.

Regards,
Cari
http://www.kantisto.nl