The term sealing refers to a situation where a disc-shaped sample has different gas compositions on separate sides of it.

The sealing is achieved by utilizing a sample support tube that has approximately the same diameter than the sample, and placing the sample at the end of that tube. Between them a sealing gasket ensures gas tightness, and the sample disc is pressed on the tube with a steady force. One type of atmosphere is led inside the sample support tube (called inner compartment), and another type to outside (called outer compartment). This arrangement allows various types of measurements and tests to be performed on the disc. Various electrode contacts, sensors, gas flow utilities, catalysts, etc. can be placed on both the inner and the outer compartment according to the needs of the test setup. Even optical port can be used to have optical access to the sample disc.