Fast and direct screening of polyaromatic hydrocarbon (PAH)-contaminated sand using a miniaturized membrane inlet mass spectrometer (mini-MIMS).

A miniaturized membrane inlet mass spectrometer (mini-MIMS; total weight 10 kg everything included) was equipped with a small sample cell using a flat sheet silicone membrane mounted close to the ionizing region of a multipole mass spectrometer. Spiked sand samples were placed in small stainless steel vials and dropped into the heated sample cell (>150 degrees C). A hole in the vial in front of the membrane and above the sand made it possible for the polyaromatic hydrocarbon (PAH) residuals to penetrate the membrane and enter the mass spectrometer as they evaporated from the sample. Using this simple setup we were able to quantitatively (approximately 10% relative standard deviation (RSD)) detect PAHs with up to five aromatic rings and with detection limits in the low parts-per-million (ppm) range. The vial system solves one of the major difficulties in analysis of larger PAHs using a MIMS. Normally, analysis of PAHs with more than two rings is hampered by a long memory effect due to the sticking of the PAHs to the inlet system, the membrane and surfaces in the vacuum system. By removing the vial from the sample cell within 2 min, we were able to analyze samples at 5-10 min intervals. The preliminary laboratory experiments presented here show much promise with respect to the development of a hand held (<10 kg) on-site mass spectrometry system for PAH screening at contaminated sites.