Quantitative Site-Specific 2~H NMR Investigation of MTBE: Potential for Assessing Contaminant Sources and Fate

摘要

Site-specific isotopic values of methyl tertiary butyl ether (MTBE) were measured using quantitative site-specific ~2H nuclear magnetic resonance (NMR) spectroscopy for seven commercially available MTBE products. The δ~2H values of the methoxy and tertiary butyl groups ranged from -103‰ to -171‰, and from -76‰ to -104‰, reflecting their production from methanol and isobutene, respectively. Several MTBE products whose whole-compound δ~(13)C and δ~2H MTBE values were within error of each other, as measured by isotope ratio mass spectrometry (IRMS), had demonstrably different δ~2H values for their methoxy and tertiary butyl groups measured by ~2H NMR. Site-specific isotopic variations were large enough to provide proof of principle that quantitative site-specific ~2H NMR may provide an additional parameter for contaminant sourcing at field sites. Isotopic variations were small enough to not bias the comparability of degradation-associated isotopic enrichment factors determined using different MTBE products. Calculated δ~2H values for MTBE, derived as weighted averages of ~2H NMR measurements of the two functional groups, showed good agreement with IRMS measurements. The ability to gain accurate information about the site-specific isotopic ratios of ~2H/~1H within a molecule offers considerable promise as a new environmental tool to track the source and fate of environmental contaminants.