δD and δ13C analyses of atmospheric volatile organic compounds by thermal desorption gas chromatography isotope ratio mass spectrometry.

This paper describes the establishment of a robust method to determine compound specific δD and δ13C values of volatile organic compounds (VOCs) in a standard mixture ranging between C6 and C10 and was applied to various complex emission samples, e.g. from biomass combustion and car exhaust. A thermal desorption (TD) unit was linked to a gas chromatography isotope ratio mass spectrometer (GC-irMS) to enable compound specific isotope analysis (CSIA) of gaseous samples. TenaxTA was used as an adsorbent material in stainless steel TD tubes. We determined instrument settings to achieve a minimal water background level for reliable δD analysis and investigated the impact of storage time on δD and δ13C values of collected VOCs (176 days and 40 days of storage, respectively). Most of the standard compounds investigated showed standard deviations (SD) < 6‰ (δD) when stored for 148 days at 4°C. However, benzene revealed occasionally D depleted values (21‰ SD) for unknown reasons. δ13C analysis demonstrated that storage of 40 days had no effect on VOCs investigated. We also showed that breakthrough (benzene and toluene, 37% and 7%, respectively) had only a negligible effect (0.7‰ and 0.4‰, respectively on δ13C values of VOCs on the sample tube. We established that the sample portion collected at the split flow effluent of the TD unit can be used as a replicate sample for isotope analysis saving valuable sampling time and resources. We also applied TD-GC-irMS to different emission samples (biomass combustion, petrol and diesel car engines exhaust) and for the first time δD values of atmospheric VOCs in the aboverange are reported. Significant differences in δD of up to 130‰ were observed between VOCs in emissions from petrol car engine exhaust and biomass combustion (Karri tree). However, diesel car emissions showed a high content of highly complex unresolved mixtures thus a baseline separation of VOCs was not achieved for stable hydrogen isotope analysis. The ability to analyse δD by TD-GC-irMS complements the characterisation of atmospheric VOCs and is maybe used for establishing further source(s)

δ13C and δD of volatile organic compounds in an alumina industry stack emission

Compound specific isotope analysis (CSIA) is becoming more widely accepted as a tool for determining the sources of contaminants and monitoring their transport and fate in the environment. However, measuring δD of volatile organic compounds (VOCs) in atmospheric samples is still underexplored. The present study applies thermal desorptione-gas chromatography-isotope ratio mass spectrometry (TD-GC-irMS) for the first time to measure stable hydrogen isotope analyses of VOCs in an alumina refinery emission. δ13C data is also collected. A sampling train was designed using TenaxTA as the adsorbent material to gain reliable and reproducible results for CSIA. δ13C values for VOCs (C6-C14) ranged from -22 to -31˚/oo, which is similar to δ13C value range reported for naturally occurring components. The δD values (21 to -137˚/oo) in this study were consistently more enriched in D compared to δD values of VOCs previously reported making the δ values of VOCs in the industrial stack unique. Therefore δD analysis may provide a means for tracking VOCs in atmospheric samples

Compound specific carbon and hydrogen stable isotope analyses of volatile organic compounds in various emissions of combustion processes

This study presents carbon (δ13C) and hydrogen (δD) isotope values of volatile organic compounds (VOCs) in various emission sources using thermal desorption–gas chromatography–isotope ratio mass spectrometry (TD–GC–irMS). The investigated VOCs ranged from C6 to C10. Samples were taken from (i) car exhaust emissions as well as from plant combustion experiments of (ii) various C3 and (iii) various C4 plants. We found significant differences in d values of analysed VOCs between these sources, e.g. δ13C of benzene ranged between (i) -21.7 ± 0.2‰, (ii) -27.6 ± 1.6‰ and (iii) -16.3 ± 2.2‰, respectively and δD of benzene ranged between (i) -73 ± 13‰, (ii) -111 ± 10‰ and (iii) -70 ± 24‰, respectively. Results of VOCs present in investigated emission sources were compared to values from the literature (aluminium refinery emission). All source groups could be clearly distinguished using the dual approach of δ13C and δD analysis. The results of this study indicate that the correlation of compound specific carbon and hydrogen isotope analysis provides the potential for future research to trace the fate and to determine the origin of VOCs in the atmosphere using thermal desorption compound specific isotope analysis