Investigation of fundamental physical properties of a polydimethylsiloxane (PDMS) membrane using a proton transfer reaction mass spectrometer (PTRMS)

A membrane introduction proton transfer reaction mass spectrometer (MI-PTRMS) has been employed for the characterisation of a polydimethylsiloxane (PDMS) membrane. For this purpose the diffusion and partition coefficients (which serve as a measure for solubility) have been determined experimentally for different classes of chemical compounds both non-polar and polar species, i.e., aromatics, alcohols, and ketones. It turned out that not only polar compounds exhibit strong interaction with a hydrophobic membrane such as the PDMS, but also non-polar compounds as trimethylbenzene or propylbenzene show strong interaction with a PDMS membrane. Stronger analyte-membrane interaction leads to a slower diffusion coefficient and larger partition coefficient. The effect of the temperature on the diffusion coefficient and partition coefficient has also been investigated, i.e., at higher temperature diffusion becomes faster and solubility lower. Permeability can be calculated from diffusion and partition coefficients and the activation energy has been derived from corresponding Arrhenius plots. The MI-PTRMS system shows detection limits in the order of tens of ppt, and its response is linear for more than four orders of magnitude. (C) 2004 Elsevier B.V. All rights reserved.