Pressure-dependent permeation of noble gases (He, Ne, Ar, Kr, Xe) through thin membranes of oriented polypropylene (OPP) studied by mass spectrometry.

A mass spectrometric method has been used to study transmission of noble ga ses (He, Ne, Ar, Kr, Xe) through thin polymer membranes of OPP and PET. The transmission of gas originating from a confined volume in a gas cell throu gh the membrane is measured by a mass spectrometer. Due to depletion of gas inside the gas cell, transmission decreases as a function of time, which i s taken as a measure for permeation. For the smaller noble gases helium and neon gas transmission is found to be an exponential function of time indic ating a pressure independent permeability for PET and OPP. For the permeati on of heavier noble gases xenon, krypton and - to a lesser extent - argon t hrough OPP a pressure dependent permeability was found. A model takes into account the higher solubility for bigger gas atoms as they have a higher pr obability to condense in cavities of the free volume of the polymer. There is good agreement between experimental and calculated data. Sensitivi ty of the mass spectrometric method is discussed for argon isotopes Ar-40, Ar-38 and Ar-36 and shows an instrumental detection limit of less than 0.1% . (C) 2001 Elsevier Science Ltd. All rights reserved.