High-precision liquid chromatography-combustion isotope ratio mass spectrometry.

Online liquid chromatography-combustion high-precision carbon isotope ratio mass spectrometry (LCC-IRMS) is demonstrated for the first time with a direct interface to the liquid source. The interface is based on a continuously coated moving wire which facilitates reproducible solvent removal and analyte combustion, followed by drying of the CO2 and admission to the mass spectrometer. Routine precision and accuracy for compounds analyzed with the interface in the flow injection mode is about delta 13CPDB = 0.5/1000 over the range -28 < delta 13CPDB < 83. Precision in the liquid chromatography mode is routinely approximately 1/1000 and is limited by sample size. This system expands the range of online compound-specific isotope ratio analysis (CSIA) to thermally labile and nonvolatile compounds.