Compound-specific stable hydrogen isotope analysis of small amount of organic compounds

Abstract

After the development of compound-specific isotope analysis (CSIA) by gas chromatograph/pyrolysis/isotope ratio mass spectrometer (GC/pyrolysis/IRMS) in the end of the 1990s, stable hydrogen isotopic composition of organic compounds has been employed for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and as a potential proxy for reconstructing paleoclimatic, paleohydrological, and paleosalinity changes. However, sample amount required for accurate and precise determination of the isotopic composition is generally 10-50nmol H for each compound, which is much larger than that of stable carbon (0.1-5nmol C) and nitrogen (1-10nmol N) on the isotope analysis by gas chromatograph/combustion/isotope ratio mass spectrometer (GC/combustion/IRMS). Here, I demonstrate the performance of GC/pyrolysis/IRMS on the small amount of samples, and suggest a mathematical correction for preventing systematic errors in the measured isotopic composition due to different sample amounts. By using this correction, the hydrogen isotopic composition of organic compounds can be determined with a standard deviation (1σ) of better than 7‰ on the sample amount of 4nmol H and even 13‰ on the sample amount of 2nmol H. This correction thus allows us easy access to the hydrogen isotopic composition of organic compounds containing with small concentration in samples.