R8 AM Contamination Source Identification and Apportionment
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in 331-332

(PEN-1117-852559) PAH Source Identification and Apportionment using SPME-GC-IRMS: Isotope Fractionation during Extraction and Analysis.

Peng, J¹, Maruya, K¹, Zeng, E², ¹ Southern California Coastal Water Research Project, Westminster, CA, USA² Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, Guangdong, China

ABSTRACT- Gas chromatography-isotope ratio mass spectrometry (GC-IRMS) is a potentially useful tool for identifying sources of trace organic contaminants. The use of solid phase microextraction (SPME) not only simplifies sample collection, its selectivity eliminates the need for costly and time-consuming cleanup steps whereas its design enables direct injection of environmental samples sorbed to SPME fibers into the GC-IRMS. The potential for isotopic fractionation during different stages of SPME extraction as well as during GC-IRMS analysis needs to be assessed, however, before this technique can be effectively used in source identification. In this study, isotope fractionation of SPME-sorbed PAHs during thermal desorption inside the GC injector was measured in a time series experiment. Second, isotope fractionation was measured for several PAHs extracted sequentially and exhaustively by multiple batches of SPME fibers under non-equilibrium conditions (1-day extraction). A third experiment involved batch SPME extraction of PAHs under equilibrium conditions (2-week extraction)until exhaustion. We observed clear fractionation during thermal desorption inside the GC injector, with isotope ratios of remaining PAHs becoming heavier (averaging +1.75 per mil) after 5 seconds of thermal desorption when over 90 percent PAHs were desorbed. There were no significant shifts in isotope ratios during sequential SPME extractions under non-equilibrium conditions. However, a clear enrichment of ¹³C during the equilibrium SPME extractions was observed, with the second batch about 1.5 per mil heavier than the first batch after 75 percent depletion of PAHs in the spiked solution. Comparatively, the isotope ratios obtained by equilibrium SPME extractions were more consistent with the true values than those obtained under non-equilibrium conditions, suggesting that equilibrium extraction is a prerequisite for SPME-GC-IRMS for source tracking. Our preliminary results suggest that equilibrium SPME-GC-IRMS analysis can be a potentially useful tool for HOC source identification and apportionment.

Key words: SPME, GC-IRMS, Source Tracking, Isotope Fractionation