The Direct Analysis of Semi-volatile Organic Compounds by Membrane Introduction Mass Spectrometry

We present results for direct on-line detection of semi-volatile compounds in air using membrane introduction ion trap mass spectrometry. Brief sampling periods of 10 seconds to 3 minutes produced linear and reproducible data for concentrations ranging from parts-per-trillion to parts-per-billion by volume. The method uses a composite membrane made by plasma deposition of a thin polydimethylsilicone layer on a microporous polypropylene support fiber. Charge exchange ionization was used for a variety of semi-volatile compounds and produced enhanced responses when compared to electron ionization. Among the semi-volatile species studied are dimethyl methylphosphonate, malathion, nitrobenzene, methyl salicylate, 2-chlorophenol, cyclohexanol, diethyl malonate and naphthalene. We also demonstrate direct analysis of semi-volatile compounds in aqueous solution with the composite membrane by the detection of 2-chlorophenol in water using both electron ionization and proton transfer chemical ionization.