Some analytical implications of the interaction between the water and oxygen permeabilities of polymers

Tubes of polythene, polypropylene, furfural polymer (‘Tygon’) or polytetrafluoroethylene are normally permeable to atmospheric oxygen when deoxygenated water flows through them. Both polypropylene and Tygon can achieve a state of impermeability after prolonged contact with water, and this is due to the steady-state water transmission through the tube-wall becoming sufficiently vigorous to exclude the oxygen that attempts to penetrate in the opposite direction. It is shown that the achievement of oxygen impermeability by this mechanism can depend on the cross-sectional dimensions of the tube. Hence only the smaller of two polypropylene tubes achieved impermeability to atmospheric oxygen. On account of the special conditions required for oxygen impermeability, it is considered that none of the four types of polymer tubing tested in this work is suitable for routine use in the sampling of water before microdetermination of dissolved oxygen.