Sensing of Petrochemical Fuels in Soils Using Headspace Analysis with Photoionization-Ion Mobility Spectrometry

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Abstract
Photoionization-Ion Mobility Spectrometry (PI-IMS) was used to distinguish among common petrochemical fuels including leaded gasoline, unleaded gasoline, kerosene, and diesel fuel through sampling of headpsace vapors over liquid samples. Positive ion mobility spectra obtained in air at ambient pressure were comprised of 3 to 5 peaks which were tentatively identified as benzene, alkylated benzenes, naphthalene and alkylated naphthalenes. The simple mobility spectra from PI-IMS analysis, due to selective ionization of aromatic hydrocarbons. were contrasted with the complex chromatographic patterns for the same fuels from scanning GC/MS analysis. Discrimination between unleaded gasoline and diesel fuel in fuel mixtures was possible using PI-IMS across a broad range of gas-phase concentration ratios. Fuels were also detected in soil using PI-IMS analysis of headspace vapors at 25[ddot]C. Unleaded gasoline in soil was detected from 0.16 to 16 mg/kg for only 0.1 g of sample with nearly linear response. Reproducibility in preparation and analysis of soil samples was 10 to 60% RSD for individual components while instrumental PI-IMS reproducibility with toluene alone was 5% RSD. Water vapor had no effect on PI-IMS response for fuel vapors alone, but increased moisture content in soils caused enhanced response. Drilling mud from a natural gas reserve pit was used to demonstrate environmental application of PI-IMS in sensing a water-saturated sample. Qualitative inspection of results showed no serious complication to PI-IMS response from water. Effects on sensor sensitivity from weathering and other environmental alterations of fuels in soils and groundwater were not explored.