[vokona]

Hello all, I am having some difficulty understanding a couple of concepts in CE that hopefully someone can help me with.

 The first involves the electro osmotic flow in CE. As far as I have it understood, the silanol groups of the capillary wall are first deprotanated to a negative charge along the capillary wall. Then when the run buffer is added, a positive charged buffer ion makes a first fixed layer next to the wall. Along with this there is a a second mobile association of positive charge associated with the wall. This double layer causes a net imbalance of charge in the bulk solution. Then when a electric potential is applied the solution flows. This makes sense, I do not understand why it is the case that most often the examples show that the flow is towards the cathode (-). Shouldn't the imbalance be in favor of the anions in the solutions since there is a fixed layer of cations next to the capillary wall and then shouldn't the flow be in the direction of the anode?

My second question concerns micelllar electrokinetic chromotography (MEKC). Why is it better at separating neutral analytes then regular CE? If the EOF is stronger than the electrophoretic mobility and the analytes are differently sized (different mass) then there will be some degree of separation in CE. Why does adding the surfactant do anything. Won't it in fact take longer now because it is a much larger and negatively charged analyte that needs to move through the capillary?

Thanks in advance.