Advances in carbon isotope analysis of trapped methane and volatile hydrocarbons in crystalline rock cores.

Rationale: The isotopic composition of hydrocarbons trapped in rocks on the microscale (fluid inclusions, mineral grain boundaries, microfractures) can provide powerful information on geological and biological processes but are an analytical challenge due to low concentrations. We present a new approach for the extraction and carbon isotopic analysis of methane (CH ) and hydrocarbons in trapped volatiles in crystalline rocks.

Methods: An off-line crusher with cryogenic trapping and a custom-made silica glass U-trap were attached to an external injector port on a continuous flow gas chromatograph/combustion/isotope ratio mass spectrometer to demonstrate the accuracy, reproducibility, and sensitivity of δ C measurements for CH .