PNNL

Abstract

A membrane introduction proton transfer reaction mass spectrometry (MI-PTRMS) has been employed for the characterisation of a polydimethylsiloxane (PDMS) membrane. For this purpose the diffusion and partition coefficients (which serves 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, 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 which bear a relevant number of methyl groups or an alkyl chain show strong interaction with a PDMS membrane. Stronger interaction analyte-membrane leads to a slower diffusion coefficient and larger partition coefficient. The effect of the temperature on the diffusion coefficient and partition coefficient is also investigated. At higher temperature diffusion becomes faster and solubility lower. Permeability is calculated from diffusion and partition coefficients and activation energy are derived from corresponding Arrhenius plots. The MI-PTRMS system shows detection limits in the order of tens of pptv and it’s linear over five orders of magnitude.