The Influence of Hydrostatic Pressure on Gas Diffusion in Polymer and Nano-composite Membranes: Application to Membrane Inlet Mass Spectrometry

A nano-composite membrane, created by coating a thin polysiloxane film to the surface of an anodic aluminum oxide (AAO) membrane, was directly coupled to the inlet system of a mass spectrometer. The gas-permeation properties of the polysiloxane nano-composite (PNC) membrane were compared to those of a conventional polydimethylsiloxane (PDMS) membrane over a range of hydrostatic pressures. Permeation of gases through the conventional PDMS membrane was reduced at high pressure by compression of the siloxane matrix. The PNC membrane had a much higher mechanical strength than the PDMS membrane, and exhibited little deviation in gas permeation at elevated hydrostatic pressure. Consistent with this difference in behavior, whereas the PDMS membrane exhibited hysteresis throughout cycles of increasing and decreasing hydrostatic pressure, hysteresis effects were substantially limited for the PNC membrane. The time required to attain steady-state diffusion through the PNC membrane was substantially reduced relative to the PDMS membrane