2.Experimental
2.1. Chemicals and reagents
Phenanthrene (PHE; 95.0%), benzo(a)anthracene (BaA; 100%), chrysene (CHR; 99.8%), benzo[b]fluoranthene (BbF; 99.4)%, benzo[k]fluoranthene (BkF; 99.1%), benzo(a)pyrene (BAP; 96.0%),and dibenzo[a,h]anthracene (DBahA; 99.6%) standards were purchased from Accustandard, Inc.(New Haven, USA). a stock solution containing 100mg mL-1 of each PAH was prepared in methanol and stored in the dark at 4•c. Working standard solutions were prepared weekly by diluting the stock standard solutions in methanol.