What luck have you had in finding this out for yourself? Where did you hear about each process, and how are they performed? In molecular biology, we often use an electrophoresis rig to separate DNA for example into bands on a gel. Then we can seal an excised band of gel containing target in a dialysis bag with buffer, put in the same rig without a cast gel, and use the current for a short time to draw the target out of the gel, and into a solution we can use. Check out some molecular biology textbooks and see if they match your question.