PAH and N-PAH were determined by using a Trace GC gas chromatograph coupled with a Trace Q mass spectrometer. For PAH and N-PAH, the detector was operated in the selected ion monitoring (sim) modality. The instrument was purchased from Thermo, Rodano MI, Italy. Separations of analyses were obtained through a 25-m-long, RT5MS-type (methylphenyl silicone stationary phase; i.d. = 250 ^m, film = 0.33 p.m) capillary column provided by Superchrom, Milan, Italy. The mass spectrometer system was operated in electron impact mode (ion source energy = 70 eV) and GC/MS data were acquired by a dedicated software (Excalibur) purchased from Thermo. n-Alkanes were processed through a second Trace GC system equipped with a similar GC column combined to a flame ionization detector.
Compounds identification was based upon comparison of eluted peaks with authentic analyze standards, GC retention times, mass spectra derived from reference (NIST) as well as home-made libraries and interpretation of mass spectrometric fragmentation patterns. Quantification of the compounds was conducted by comparing GC peak areas with those of known co-injected standards (internal standard method), after checking for the concentrations lied within the detector operative ranges (usually 3-1000 times the respective detection limits). Filter blanks, occurring only for some semivolatile n-alkanes (up to C18), phenanthrene and pyrene among PAH, were subtracted to obtain neat aerial concentrations of compounds. Analytical uncertainty in any case did not exceed 15%.
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