An optical approach for compound specific carbon isotope analysis of 1,4-dioxane by liquid injection

Abstract

Compound specific stable isotope analysis (CSIA) is an emerging tool to identify sources of organic compounds as well as their degradation pathways in environments. In recent years gas chromatography coupled to isotope ratio infrared spectroscopy (GC-IRIS) has been increasingly applied to monitor carbon isotopic compositions of gas molecules including methane, ethane and propane. Very recently, we developed an optical CSIA method based on a mid-infrared laser to analyze carbon isotopic compositions of volatile organic compounds including benzene, toluene, ethylbenzene and xylene. However, further development and validation are needed in order to analyze stable carbon isotopic ratios of hydrophilic compounds such as 1,4-dioxane. To this end, we adopted liquid injection mode in the GC-IRIS method and achieved a detection limit of minimal 100 ng on-column carbon (equivalent to 185 ng of 1,4-dioxane), which corresponds to a precision of ±0.1‰. Moreover, our approach was cross-validated by comparing the obtained δ¹³C values with the ones determined by using the conventional IRMS methods. Lastly, our approach was successfully applied to characterize 1,4-dioxane from different manufacturers. To the best of our knowledge, this is the first validated optical carbon CSIA approach proven to be suitable for hydrophilic organic compounds in water.