the second channel segment that is sufficient to substantially eliminate a differential driving force between the first end of the first channel segment and the first fluid junction, and selectively applying a third differential driving force through the third channel segment sufficient to substantially eliminate a differential driving force between the second fluid junction and the second end of the first channel segment.

2. The method of claim 1, wherein the first differential driving force comprises a pressure differential applied between the first and second ends of the first channel segment.

3. The method of claim 1, wherein the first differential driving force comprises an electrical differential applied between the first and second ends of the first chaimel segment.

4. The method of claim 1, wherein the differential driving force comprisesstep of applying the first differential driving force comprises applying a positive pressure to the first end of the first channel segment.

16. The method of claim 1 , wherein the step of applying the first differential driving force comprises applying a negative pressure to the second end of the first channel segment.

17. The method of claim 16, wherein the step of applying the first differential driving force further comprises applying a positive pressure to the first end of the first channel segment.

18. The method of claim 1 , wherein the differential driving force between the first end of the first channel segment and the first fluid junction is at least 90% eliminated.

19. The method of claim 1 , wherein the differential driving force between the first end of