Stable carbon and hydrogen isotope analysis of methyl tert-butyl ether and tert-amyl methyl ether by purge and trap-gas chromatography-isotope ratio mass spectrometry: Method evaluation and application

Abstract

In order to monitor the behaviour of contaminants in the aqueous environment effective enrichment techniques often have to be employed due to their low concentrations. In this work a robust and sensitive purge and trap-gas chromatography-isotope ratio mass spectrometry method for carbon and hydrogen isotope analysis of fuel oxygenates in water is presented. The method evaluation included the determination of method detection limits, accuracy and reproducibility of δD and δ¹³C values. Lowest concentrations at which reliable δ¹³C values could be determined were 5 µg L⁻¹ and 28 µg L⁻¹ for TAME and MTBE, respectively. Stable δD values for MTBE and TAME could be achieved for concentrations as low as 25 and 50 µg L⁻¹. Good long-term reproducibility of δ¹³C and δD values was obtained for all target compounds. But δD values varying more than 5‰ were observed using different thermal conversion tubes. Thus, a correction of δD values in the analysis of groundwater samples was necessary to guarantee comparability of the results. The applicability of this method was shown by the analysis of groundwater samples from a gasoline contaminated site. By two dimensional isotope analysis two locations within this site were identified at which anaerobic and aerobic degradation of methyl tert-butyl ether occurred.