Abstract
Compound-specific hydrogen isotope analysis of polycyclic aromatic hydrocarbons (PAHs) has been established at sub-nano molar level, using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). The analytical precision of δD value is generally less than a few ‰ at >2nmol (i.e. 20ng H) injection of pyrene and fluoranthene calibrated with co-injected 30ng H of phenanthrene and chrysene.
Hydrogen isotope exchange of pyrene and fluoranthene with water under neutral and acidic conditions was examined with relevance to hydrogen isotopic distribution of individual PAHs in carbonaceous chondrites. Hydrogen isotope exchange between PAH and water hardly occurred at 170℃ under neutral pH condition for 2 days. However, under acidic condition (pH=2), the isotope exchange reaction occurred, where hydrogens have exchanged more easily between pyrene and water relative to between fluoranthene and water. The kinetically different behavior between pyrene and fluoranthene coincides with the two-series PAH formation mechanisms in carbonaceous chondrites inferred from carbon isotopic compositions of PAH.
