Question

A negatively charged sample would be expected to migrate towards the anode (positively charged electrode). How then is it that species of all charges are detected in capillary electrophoresis at the cathode (negatively charged) end of the system

Answer 1

Because Capillary electrophoresis separates ions based on their electrophoretic mobility with the use of an applied electric field. The mobility of ions is dependent upon various factors such as the charge of the ion, the viscosity, and the ion's radius. The mobility is directly proportional to the applied electric field. Neutral species are not affected, only ions move with the electric field so you will have neutral species around the cathode. If two ions are the same size, the one with the greater charge will move the fastest so you can have larger negative ions around the cathode also. For ions of the same charge, the smaller particle faster migration rate.

From the above paragraph, we can see that a larger anion can be found near cathode due to its lower mobility and cations are found near as opposite charges attract each other and neutral can be found as they are not affected at all.

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