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Determination of the Radiocarbon Ages of Individual PAH Extracted From Urban Aerosol and Marine Sediment: Prepurification, GC Separation, and AMS Analysis of Microgram-Sized SamplesEPA Grant Number: U915153
Title: Determination of the Radiocarbon Ages of Individual PAH Extracted From Urban Aerosol and Marine Sediment: Prepurification, GC Separation, and AMS Analysis of Microgram-Sized Samples
Investigators: Pearson, Ann
Institution: Massachusetts Institute of Technology
EPA Project Officer: Broadway, Virginia
Project Period: January 1, 1997 through January 1, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1997) RFA Text | Recipients Lists
Research Category: Fellowship - Oceanography , Academic Fellowships , Aquatic Ecosystems
The objective of this research project is to determine whether the unregulated combustion of modern biogenic material may contribute a significant fraction of the polycyclic aromatic hydrocarbons (PAHs) found in marine sediments by combining molecular-level stable carbon and radiocarbon isotopic ratios (d13C, D14C) to yield quantitative source apportionment in two isotopic dimensions.
Determination of the molecular-level 14C content of trace organic compounds extracted from natural samples presents several analytical challenges. Identification and quantitation of organic molecules by gas chromatography/mass spectrometry (GC/MS) is typically performed at nanogram detection levels. Although advances in 14C dating by accelerator mass spectrometry (AMS) have greatly reduced sample size requirements, microgram quantities of carbon are still required. Our laboratory has developed an analytical approach, based on preparative capillary gas chromatography (PCGC), which provides a practical means to isolate purified organic compounds in amounts sufficient for AMS 14C analysis.
Automated PCGC isolation of individual compounds is achieved using a specially designed, high capacity, CGC. Five mL of a complex mixture is injected into the system; 1 percent of the effluent passes to a flame ionization detector, and the remaining 99 percent is collected cryogenically in a series of seven U-tube traps. Six traps are programmed to collect compounds of interest; the seventh "waste" trap received the remainder of the mixture. The resulting samples of purified organic compounds can contain up to several hundred micrograms carbon, suitable for AMS 14C analysis.