A Laser Desorption Laser Photoionization Mass Spectrometry (LDLPMS) technique has been developed for the direct screening of polycyclic aromatic hydrocarbons (PAHs) in as-received soot and fly-ash samples. The method employs pulsed IR desorption from the surface of particulate matter collected on air sampling filters, followed by UV laser multiphoton ionization of the desorbed molecules. The ions thus formed are mass-analyzed in a custom-built time of flight mass spectrometer. Photoionization of PAH standards at 266 nm procedures intense parent molecular ion peaks with little or no fragmentation, allowing identification via molecular weight determination. The application of the method to the detection of PAHs in rice soot samples is demonstrated. The level of detection for PAHs is estimated to be 10-20 ng/sample, which is well within the low resolution target detection limit for ARB Method 429.
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