Determination of nitrated polycyclic aromatic hydrocarbons in particulate matter 2.5 by laser ionization mass spectrometry using an on-line chemical-reduction system.

Nitrated polycyclic aromatic hydrocarbons (NPAHs) were separated by gas chromatography (GC) and were introduced into a reactor consisting of an inner-seal Y-connector for the on-line chemical reduction of NPAH using hydrazine monohydrate as a chemical reducing agent. The reduced forms of amino polycyclic aromatic hydrocarbons (APAHs) were then determined by multiphoton ionization time-of-flight mass spectrometry (MPI/TOF-MS) using a femtosecond laser as the ionization source. Three standard samples of NPAHs, i.e., 9-nitroanthracene (9-NANT), 3-nitrofluoranthene (3-NFLU), and 1-nitropyrene (1-NPYR), were confirmed to be completely reduced to the corresponding APAHs, i.e., 9-aminoanthracene (9-AANT), 3-aminofluoranthene (3-AFLU), and 1-aminopyrene (1-APYR). The sensitivity of the method was improved by 2-8 fold by converting the NPAHs to APAHs. This analytical technique was applied to a sample extracted from PM2.5 collected in Fukuoka. The signal enhancement and background reduction by the chemical reaction resulted in the NPAHs in the actual sample being more efficiently measured, and the concentrations of 9-NANT, 3-NFLU, and 1-NPYR were determined to be 25, 305, and 217 pg m-3, respectively.