For permeation measurements with hydrogen fluoride and hydrofluoric acid a special top part of the NW50liquid cell is required as the standard top part for the NW50 permeation cells is made of glass. The vapors of the chemicals for the attack the glass and destroy it in the medium term.

Therefore, a lid made of PTFE is recommended for permeation measurements with these two chemicals. It replaces the standard cover of the permeation cell NW50 and can be used without further adjustments. Compared to the lid of the NW50liquid cell, the version on PTFE cannot be tempered with water via the thermostat.

The lower part made of glass can still be used, since the concentration of the permeation liquid is low even in the case of total breakthrough in the collection medium.