Direct determination of soil surface-bound polycyclic aromatic hydrocarbons in petroleum-contaminated soils by real-time aerosol mass spectrometry

Soil surface-bound polycyclic aromatic hydrocarbons (PAHs) were identified by use of Real-Time Aerosol Mass Spectrometry (RTAMS) in two NIST standard research material (SRM) soils (Montana SRM 2710 and Peruvian SRM 4355) each contaminated separately with three common petroleum hydrocarbons (diesel fuel, gasoline, and kerosene). The described contaminated soil analysis required no sample preparation. Direct laser desorption/ionization mass spectrometric analysis of individual soil particles contaminated with each of the petroleum hydrocarbons at three different contamination levels (0.8, 8, and 80 ppth (wt/wt)) yielded detectable PAH cation distributions that ranged from m/z 128 to 234, depending on the fuel contaminant. The same analysis performed on uncontaminated SRM soils revealed very little (Peruvian) to no (Montana) detectable PAH species. Size analysis showed that most of the individual soil particles analyzed were between 1 and 5 microm in diameter. Tandem mass spectrometry (MS/MS) experiments identified alkyl-substituted two- and three-ringed PAHs in all three petroleum hydrocarbon contaminated soils. However, due to similarities in fragmentation patterns, MS/MS analysis of higher MW species (m/z > 200) was unable to distinguish between the possibility of highly alkyl-substituted three-ringed PAHs and hydrogenated four-ringed PAHs. The described technique offers the direct, rapid determination and characterization of surface-bound PAHs in petroleum-contaminated soils at part-per-million levels without prior extraction, separation, or other sample preparation methods.