Electro-Osmosis and the Brookhaven Solution

• In most commercial electrode systems, the field lines cut across the charged walls of the cell
• Electroosmotic movement of the liquid occurs
• In a closed cell this forces a flow along each wall and back down the center (as shown below)
• In between a plane must exist where the velocity is zero - these are the stationary planes
• The measured velocity of particles anywhere in the cell is the sum of electrophoretic and electroosmotic velocity
• Valid measurements can only be made at the stationary planes

"A 10 micron error in the stationary level can lead to a 10% error in zeta potential" - Prof. Bob Pelton, University of Toronto.

Stationary plane locations must be verified whenever electro-osmosis occurs.

• Whenever the cell is removed
• Whenever the temperature changes
• Regularly in case of contamination

The Uzgiris-Brookhaven electrodes - no electroosmosis

• The ZetaPlus electrodes are entirely within the cell
• The liquid completely surrounds the electrodes
• The electric field does not cut across the cell walls

• Focus is not critical
• Cell position is not critical
• Simple, inexpensive, disposable sample cell
  • No cross contamination
  • No cleaning
  • No effect from sedimenting particles
• No electroosmotic effect!!!