Mass spectrometer based gas permeation apparatus

An instrument to measure diffusion and permeation rates in polymeric materials is described. The instrument utilizes a quadrupole mass spectrometer as a sensitive flow meter to detect the flux of gas through a polymer sheet that is subjected to a pressure gradient. The permeation coefficient is obtained from the steady state flux and the diffusion coefficient from the kinetics of reaching the steady state in a sheet that is initially devoid of permeant. The diffusion coefficient depends solely on the time development of the mass spectrometer signal and calibration is not required. The mass spectrometer output is calibrated by effusing a known quantity of the test gas into the spectrometer through an orifice. Enclosure of the sample cell in an oven permits derivation of the temperature dependences of the diffusion parameters.