At the start of a liquid-liquid measurement, the heavy phase (water) is first poured in the trough. Sink the liquid-liquid Wilhelmy plate approximately half way to the heavy phase and check the surface cleanliness with compression. Then the lighter liquid is very carefully poured on top. You can pour it on the step that widens at the liquid-liquid interface. Be careful not to pour it directly on the heavy phase as this may lead to phase mixing. You need enough light phase liquid to cover the entire Wilhelmy plate, the plate should not be in air. Open the barriers, zero the balance and inject your material into the interface. Wait a reasonable time for the specimen to stabilize at the interface and begin your measurement in a standard manner. See detailed measurement instructions from the LB user manual and Monolayer kit manual for a standard measurement.
Clean the Wilhelmy plate by flushing it with pure ethanol and water and subsequently burn it with a Bunsen burner (ca. 1000⁰C flame). Low heat flames will leave residues on the plate which can lead to significant error. Hold the plate in the hottest part of the flame for a few seconds until the plate glows red-hot. Take the plate away from the flame before turning the flame off to avoid residues from low heat. Clean the plate before and after use.
The trough and barriers are made of Teflon and Delrin. A standard trough is made of Teflon and standard barriers of Delrin. If you are not sure if you have a standard system, you can find out the materials by placing a drop of water on both the trough and barriers. The droplet will have a high contact angle on Teflon, and a low contact angle on Delrin.
Use rubber gloves while handling the components. Remove the trough and barriers and wash them by a sink. Use a soft brush to cover the entire area with pure ethanol and then rinse with pure ion exchanged water. Delrin which is used to make the barriers does not tolerate chloroform, but chloroform or other cleaning agents can be used to wash the Teflon trough. When a longer period of time has passed since the last use of the trough it can be good to wash the trough with a commercial detergent first.