Question

In capillary electrophoresis, how does switching the mode from positive polarity mode to negative polarity mode affect separation? Does the elution order change? Also how does a switch affect electroosmosis and electrophoresis?

Answer 1

In electrophoresis capillary, the ions are separated based on their electrophoretic nature using applied electric field. So, if the polarity is reversed, the direction of the applied field also reverses. This is surely going to affect the charged species. The elution order will definitely be reversed. The charged species will be separated just that the order of elution will be opposite.

The electroosmosis process happens when the applied electric field is more. Then there is a negative charge on the cappilary wall because of SiO-. The cations form a double layer on it. The inner layer is thus positive and stationary. Whereas the outer layer is free to move. Thus the reversal of polarity is anyway not applicable to electroosmosis.

Electrophoresis is affected as the cathode becomes the anode and anode becomes cathode. So the ions start moving in opposite directions.

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